Last partial update: August 2019

 

Incidence of breast cancer

Breast cancer is the most common cancer in Australian women (28% of all female cancers) and causes the most cancer deaths (19%). About 18,000 new cases of breast cancer occurred in Australian women in 2018 (and another 1,550 cases of non-invasive cancer; called ductal carcinoma-in-situ); and about 110 cases in men. In 2006, 2,618 deaths occurred. (Breast cancer is the second commonest cause of cancer death in women. (Sadly lung cancer, an almost totally preventable disease, is now the commonest cause of cancer death in women.) Breast cancer will affect one in twelve women during their lifetime, with the risk increasing with age.

 

As well as being the most the most common female cancer, breast cancer also occurs relatively early compared to other common cancers, with the average age at diagnosis being 60 years. Overall breast cancer accounts for 26% of the female cancer disease burden but in the 35 to 54 year age group, it accounts for a massive 37%. For these reasons, decreasing the incidence of breast cancer is of paramount importance in reducing overall female cancer death and disability in Australia.

 

Luckily, the death rate has fallen about 25% in the past 30 years, with the rate now at its lowest recorded rate (22 breast cancer deaths per year per 100,000 women). This is mainly due to better treatment;, although earlier diagnosis through increased use of mammography screening has alsp contributed sigificantly. Survival rates are also improving; in 2016, 89% of women remained alive five years after diagnosis. (It was only 73% in 2000.) If the breast cancer is confined to the breast at diagnosis, the five year survival rate is 98%.

 

Breast cancer is significantly more common in women who were born in the United Kingdom, Ireland, and north -western, southern and eastern Europe. It is much less common in Indigenous women, who have about half the incidence of western women, and Asian women, who have only about 10% to 20% of the incidence of western women.

 

About 5% of breast cancers occur in women under the age of 40 years.

 

 

Incidence of breast cancer in Australian women with no family history of breast or ovarian cancer.

 

Age

Risk of developing breast cancer

in the next 10 years

20

1 in 2000

30

1 in 250

40

1 in 70

50

1 in 40

60

1 in 35

70

1 in 30

 

 

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What causes breast cancer?

Breast cancer arises because a single cell in either a breast milk duct (in 80% of breast cancers) or milk sac (a lobule) (in 15% of breast cancers) is transformed by a series of gene changes (mutations) to become cancerous. (A milk duct is a ‘tube of tissue’ that takes milk from the milk sacs (lobules) where it is produced to the nipple.) This transformation disrupts normal genetic control of the cell’s growth, allowing it to grow abnormally quickly and divide more rapidly.

 

Breast cancer - Breast diagram

Source: National Cancer Institute, 2009.

 

 

While these genetic changes can be inherited, the large majority are acquired during life due to damaging influences on the cell’s genes, such as cancer causing chemicals. These acquired changes occur more commonly with increasing age. Gene changes that are acquired through life only occur in the affected cells and can not be passed on to the affected woman’s children (unless they affect an egg cell; ovum). Thus, in contrast to commonly held beliefs, most women with a family history of breast cancer in one relative only do not inherit a predisposition to cancer from their affected relative.

 

In a small percentage of cases (about 5 per cent of breast cancers), cancerous gene changes are ‘handed down’ from parents (i.e. inherited) as the gene changes are present in every cell of the person’s body. Inherited genetic mutations can be from the woman’s father or mother, so it important to look for breast cancer in both sides of the family, including breast cancer in males. Family history is more significant in increasing the risk of having inherited breast cancer when:

While most women with a family history of breast cancer will not develop the disease, all women with any family history should discuss the matter with their general practitioner. Further information can be sourced at the BreastScreen Victoria website. https://www.breastscreen.org.au/PDFs/BSV_factsheet_Family_History.

 

(Genetic / inherited breast cancer is discussed further at the end of this chapter.)

 

 

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Types of pre-breast cancer / breast cancer

As with most types of cancer, the transformation of a cell from being normal to being cancerous takes time and there are numerous pre-cancerous forms of breast cancer that occur. The progression from normal breast duct cells towards cancer roughly follows this sequence. (Most breast cancers (about 80%) originate from breast duct cells.)

Sentinal lymph nodes: Generally metastatic breast cancer will spread first to the lymph nodes in the arm pit adjacent to the breast in which the tumor is located. The lymph node that tumor cells are likely to spread to first is called the sentinal node and it can be found by injecting dye into the breast around the nipple and tracing the dye to find which lymph node it initially goes to. This sentinal node can then be surgically removed and examined for the presence of breast cancer cells. If none are present, then it is very likely (but not absolutely certain) that the cancer has not spread beyond the breast tissue. In most cases a negative sentinal node biopsy means that other lymph nodes in the axilla do not need to be removed. (This is important as the removal of all the lymph nodes in the axilla is usually associated with chronic shoulder stiffness, arm discomfort and swelling.)

Breast cancer tissue receptor status: There are several receptors that vary in their presence on breast cancer cells and that are important in determining prognosis and treatment options and which therefore can influence patient outcomes. Their presence or abscence is determined by immunohistological staining of biopsied cancer tissue. They include:

1. Oestrogen receptors (ER) - Strongly positive ER status in a high proportion of tested cancer cells usually implies a better prognosis.

2. Progesterone receptor (PR) - Strongly positive PR status in a high proportion of tested cancer cells usually implies a better prognosis.

3. Human epithelial growth factor receptor 2 (HER2) - Over expression of this receptor usually implies a worse prognosis.

Tumors that are ER / PR positive and HER2 negative tend to be more sensitive to hormone therapy better and less to chemotherapy.

 

Other much less common types of breast cancer: There are also much less common ‘lobular’ types of pre-cancerous lesions called atypical lobular hyperplasia and lobular carcinoma in situ (LCIS). These originate in the milk-producing breast lobules and may also develop into invasive carcers (either lobular or ductal cancers). LCIS is more likely to occur in multiple sites and in both breasts. Lobular cancers account for about 15% of breast cancers. Additionally, there is a type of tumor called a Phyllnode tumor which arises from fibro-epithelial tissue. These can vary from being benign to malignant. There are also several other rare types of cancer that occur in breasts, such as lymphomas and sarcomas.

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Ductal carcinoma in situ. (DCIS)

DCIS is an abnormal proliferation of cells in the mammary (milk) ducts that is confined to those milk ducts. It is usually small and not associated with a palpable lump. Thus it is usually a diagnosis that is made following the biopsy investigation of an abnormality found during screening mammography. (It is commonly seen as micro-calcification in a mammogram.) In 2006 about 11 per cent of all breast cancers found and about 20 per cent of the cancers found through screening mammography are DCIS. (Before screening mammography DCIS used to account for just two per cent of all breast cancers.)

DCIS is by far the most common pre-invasive breast cancer lesion, with about 1200 women being diagnosed each year in Australia. However, DCIS is a much less common diagnosis than invasive breast cancer, the ratio being about nine to one; although the increasing use of screening mammography is increasing the number of women being diagnosed with DCIS.

Just how common DCIS is is uncertain, but evidence from autopsy studies of women who have died in middle age from causes other than breast cancer suggest that the incidence could be as high as 30 to 40 per cent. As only about 10 per cent of women develop breast cancer, most of these lesions obviously never become a problem. The chance of a DCIS lesion developing into invasive breast cancer is thought to be about 30 to 50 per cent over a 10 to 20 year period.

There is no doubt that DCIS progresses to invasive cancer in some women but unfortunately it is not possible to tell how often this occurs or in which ones it is likely to happen. For this reason, DCIS is always removed, either by complete local excision, the more common choice, or by mastectomy. The choice depends on many factors including tumour size and grade, mammography appearance and, of course, patient preference. As the tumor has not spread, removal of lymph nodes in the arm pit (axilla) is not usually necessary. (There are some exceptions to this rule.)

The recurrence rate following mastectomy is about 1.4 per cent. If local excision alone is chosen, there is a recurrence rate of about 22 per cent and about half of these recurrences are invasive cancer, not just DCIS. This recurrence rate is halved if radiotherapy is also undertaken and for this reason radiotherapy is usually recommended following surgical treatment for DCIS. Women who opt to have local excision rather than mastectomy are advised to have more frequent mammograms and examinations by their doctor than is normally the case.

Treatment with the drug tamoxifen is not usually recommended but is occasionally used in treating DCIS. Chemotherapy is not used to treat DCIS.

Unfortunately, and contrary to what would be expected, while the treatment of DCIS has benefited individuals, it has not decreased the incidence of invasive breast cancer in the general community.

 

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Breast Cancer Risk Factors

A number of factors (listed below) can increase the risk of developing breast cancer. Some cannot be modified but some can.

Non-modifiable risk factors – Risk factors that can’t be changed

Modifiable risk factors – Risk factors that can be changed

Modifying these risk factors can significantly reduce a woman’s risk of breast cancer.

Benefit from reducing modifiable breast cancer risk factors

 

Risk factor

Modification required

Approximate reduction in risk of breast cancer

Excessive weight

Avoiding a weight gain of more than 5kg after the age of 18 years

(Losing weight later in life is also of significant benefit.)

20%

Inadequate recent exercise

Partaking in moderate physical activity for over 5 hours per week in the previous year

15% to 20%

Consuming alcohol

An alcohol intake of less than 1 drink per week for the previous year

6%

Avoiding the use of hormone replacement therapy

Ceasing the use of hormone replacement therapy

5%

All of the above

 

40%

 

Assessing overall breast cancer risk

The Cancer Australia has developed an online resource that women can use to assess their overall risk of breast cancer. This comprehensive assessment tool is available at: https://canceraustralia.gov.au/affected-cancer/cancer-types/breast-cancer/your-risk/calculate

Stress and breast cancer - No known link

Stress has been researched in some depth to see whether it is a cause of breast cancer. At this time (March 2011) there is no good evidence that it has any influence.

Soy products and breast cancer - No strong evidence of benefit

The consumption of soy products has for some time been considered beneficial by many in the community with regard to preventing breast cancer. To date there has only been limited evidence to suport this view and thus the benefits should only be regarded as possible. Current research shows that it is safe to eat moderate amounts of soy foods (e.g., soymilk, tofu), up to two to three servings per day.

 

 

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Preventing illness from breast cancer

This depends on doing both of the following.

A. Attempting to prevent breats cancer from occurring by minimising exposure to modifiable risk factors (See above).

While several important risk factors, such as age and family history can not be altered, optimising alcohol intake, weight and physical activity level can achieve significant benefits (see above) for women with these risk factors.

B. Attempting to detect pre-cancerous lesions and early cancers early enough to enable a permanent cure

Breast cancer may exist for long periods as a non-spreading or locally spreading tumor before becoming malignant (i.e. spreading to other parts of the body). This delay allows time for early detection and curative treatment. There is a 90 per cent survival rate at five years after diagnosis when the cancer is contained within the breast at diagnosis compared with an 18 per cent survival rate at five years when the disease has spread beyond the breast. Early detection can be achieved by the following.

Information relating to the topic 'Attempting to detect pre-cancerous lesions and early cancers early enough to enable a permanent cure' will now be discussed in detail.

The use of complimenary and alternative medicines to help prevent breast cancer

Many such products are used in the hope that they may the risk of developing breat cancer, including black / blue cohosh, chastebury, fenugreek, kava, dong quai, ginger, red clover, saw potato, wild yarn and metals such as calcium, magnesium and zinc. While some may provide a beneficial protective effect through oestrogen reduction, this has not been scientifically proven and adverse effects can occur. (Less regulation of this industry means dose irregularities and contamination with other products are more likely to occur.)

 

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Recognising changes in the breast that indicate cancer may be present

Reporting changes in a breast as soon as they are evident is vital for the early diagnosis of breast cancer. Any one of the symptoms listed below can by itself indicate that breast cancer is present and needs immediate investigation.

The most common cancerous change observed is a lump, which is present in about 75 per cent of cases. However, there does not have to be a lump felt for cancer to be present. Most lumps (about 90 per cent) will not prove to be cancerous but ALL must be checked to exclude cancer.

 

All women should ensure that they know what their breasts feel like and should report any change they find to their doctor. Regular breast self-examination has for a long time been part of this process and, although it is not certain that it reduces breast cancer deaths, it is a worthwhile addition to continually monitoring breasts for changes.

 

Once identified, symptoms that may indicate a breast cancer is present need to be investigated quickly and thoroughly. There are three components to investigating a breast symptom (the ‘triple test’).

 

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The Triple Test

If any one of the three components of the ‘triple test’ (outlined below) indicate a possible or likely risk of breast cancer, the ‘triple test’ is said to be positive and further investigation is necessary, usually by a surgeon experienced in the treatment of breast cancer. Used well, the triple test will diagnose about 99 per cent of breast cancers. The three components are:

  1. Appraisal by the woman’s doctor (i.e. taking a history and performing an examination)

  2. Investigation by imaging.

    Imaging investigation should include BOTH a diagnostic mammogram and an ultrasound. (Overall, about 10% of breast cancers are NOT detected by mammography alone. This figure is reduced when an ultrasound is also done and thus both should be performed before a negative imaging result is determined. Young women especially benefit from having both tests.) Generally, ultrasound is used first if the woman is under 35 years of age and mammography is used first if the woman is over 35. Newer full field digital mammography techniques require less breast compression and are thus less uncomfortable. (Medicare-funded MRI imaging is also available in Australia but only for women who are at high risk due to genetic abnormalities.)

  3. Biopsy of the lesion either by performing core biopsies (CB) of the lesion or fine needle aspiration biopsy (FNAB) of the lesion

    Biopsies are most commonly done by core biopsy, which has largely replaced fine needle biosy as the method of choice. Usually three biopsies are taken under ultrasound or mammography guidance to ensure the correct area is biopsied. This component of the triple test should be done last as;

      • bleeding that can occur with these procedures can make clinical examination and imaging interpretation difficult.
      • diagnostic mammography often needs to be done prior to these procedures to help determine the area(s) that require biopsy.

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Further detail regarding the biopsy of breast lesions

 

Fine needle aspiration biopsy (FNAB) and core biopsy (CB)

The only way of truly determining the nature of a breast lump or other breast abnormality is for a pathologist to microscopically examine cells from the area affected. This can be done by either fine needle aspiration biopsy (FNAB) or core biopsy (CB). FNAB yields either individual cells or small fragments of tissue while CB, which uses a wider bore biopsy needle, delivers larger fragments that also show the ‘structure’ of the affected breast tissue.

 

Both FNAB and CB are very good at assessing lumps that can be felt. Abnormalities that can not be felt, which are commonly found by mammography, are harder to assess accurately. However, in good hands, FNAB will pick up more than 94 per cent of cancers with CB giving better results again. About 25 per cent of FNABs and 12 per cent of CBs provide inadequate tissue to allow a diagnosis to be made. (A surgical excision biopsy is usually required to make a definite diagnosis in these circumstances.)

 

There are many variables that help determine which technique is best for a particular lesion. The larger specimens gained from taking a CB make it preferable in the following circumstances.

  1. When a woman is being investigated for lesions found by mammography, especially microcalcifications (and also small lesions and radial scar lesions). FNAB of these lesions often provides an inadequate specimen.
  2. When trying to decide whether ductal carcinoma in situ (DCIS) or actual invasive cancer is present, as differentiating between the two requires structural information about the breast tissue. While CB can diagnose invasive cancer, it is important to realise that if CB only finds DCIS, this does not exclude the presence of invasive cancer (as it may be present in tissue adjacent to the site biopsied). FNAB does not provide a large enough tissue specimen to distinguish between high grade DCIS and invasive cancer.
  3. To make a more definitive diagnosis of some lesions, including atypical ductal hyperplasia, low-grade DCIS, some tubular carcinomas and some invasive lobular carcinomas. (CB still has difficulty in differentiating atypical ductal hyperplasia and low-grade DCIS.

If the lesion being biopsied is small or difficult to feel, then using imaging techniques such as mammography or ultrasound at the time of the biopsy will help accurately locate the lesion and make sure the correct area is biopsied.

Newer biopsy techniques

 Directional vacuum-assisted biopsy. This technique is being used to help make CB more accurate and simpler. Previously, the CB needle needed to be removed each time a CB specimen was taken and then re-inserted. (Multiple specimens are always required.) As the specimens are sucked out using this technique, it allows multiple CB specimens to be taken without removing the needle. It is thus good for evaluating difficult lesions that are hard to feel.

Large CB biopsy techniques. These allow a larger specimen which makes diagnosis easier.

Clinician experience and competence are important

The clinical experience of the person taking the biopsy is a very important factor in determining how well the biopsy is performed. Thus, women need to ensure that they are referred to clinicians experienced in performing these procedures if they need a biopsy done. Many clinicians perform these procedures including surgeons, breast doctors, radiologists, GPs, and pathologists. Often, a clinic specializing in investigating breast abnormalities (if locally available) is a good place to start. Importantly, such clinics will use or refer to radiologists and pathologists experienced in investigating breast abnormalities.

 

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Why do women delay presenting with breast cancer symptoms? 

 

Unfortunately many women with breast cancer symptoms still delay consulting their doctor about the symptom. This is a serious problem as early detection is the main method by which death from breast cancer can be avoided. (As mentioned above, about 90% of early breast lumps can be cured.).

 

The delay is usually due to:

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Breast cancer in young women - But I’m too young??

While the incidence of breast cancer increases with age, about 6 per cent of breast cancers occur in women under the age of 40 years; an incidence of about one in 200 women under 40. About 1% occur in women under 30 years of age and at the end of 2006, there were about 170 women in Australia under the age of 30 years who had at some time been diagnosed with breast cancer.

Thus, all younger women with a new breast symptom, particularly a lump, need to see their doctor immediately to organise a prompt full investigation of the abnormality that provides them with an accurate diagnosis. Most will not be cancer but it is dangerous to assume this to be the case.

Unfortunately, breast cancer in younger women also carries a worse prognosis, mainly because the cancers are generally found later than in older women. Reasons for this include that:

  1. the cancers themselves tend to be more aggressive in nature
  2. mammography screening is not done in this age group and
  3. cancer is much less common in this age group, leading to a lower level of suspicion amongst medical practitioners and thus less urgent investigation.

Imaging investigation of breast lumps by mammography in women under 40 years of age is much less accurate, partly because their denser breast tissue can obscure lesions and partly because cancerous lesions in younger women often do not have the features usually seen in a mammogram of a cancerous lesion. Ultrasound is probably more accurate in diagnosing cancer in the under-40 age group and should be the first choice imaging technique in this group, although in practice many younger women end up needing both ultrasound and mammography. These investigations will usually correctly identify benign simple (fluid filled) cysts. However, any lesion that is not a simple fluid filled cyst (i.e. a lesion that has any solid component) requires biopsy to achieve adequate diagnostic accuracy; that is, it needs all three components of the ‘Triple Test’. This includes lesions that imaging indicates as being probable benign fibroadenomas, as some of these turn out to be cancers on biopsy. (Fibroadenomas are the most common benign breast lump, especially in younger women.) Even benign cysts can be aspirated to reduce their size and the fluid removed can be checked for cancer cells. (Benign cysts that disappear with aspiration will sometimes refill with fluid.)

 

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Screening mammograms

Mammograms are X-rays of the breast and can be done for two different reasons. Firstly, they can be done as a screening test to help find abnormalities in breasts that look and feel normal (i.e. no lump or other abnormality has been previously found). This test is called a screening mammogram and is the type of mammogram that we are referring to in this section. It is generally not performed by a doctor.

 

Mammograms can also be done to help diagnose the nature of a lump or other abnormality that has already been found. This is called a diagnostic mammogram. It involves more X-Rays and is interpreted by a doctor (a radiologist). All mammograms are X-Rays, not ultrasounds.

 

In Australia, screening mammograms are available free of charge for all women over 40 years of age through BreastScreen Australia. (See below for details.) In the two year period 2005/6, between 52 to 59 per cent of women in Australia in the target age group of 50 to 70 years had mammograms. (The lowest rate was in women aged 50 to 55 and the highest was in women aged 65 to 70.) Understandably rates were lower in very remote areas (about 49%).

 

Thermography and other alternative breast screening procedures

The only breast screening technology recommended by the National Breast and Ovarian Cancer Centre of Australia (NBOCC) is screening by mammography. With regard to Thermography, a technology that is recommended by some people as an alternative / adjunct to mammography screening, the NBBOC website states (June 2009) that:

 

‘There is no current scientific evidence to support the use of thermography in the early detection of breast cancer and in the reduction of mortality.’

 

(Thermography, also called thermal breast imaging, measures the temperature of the skin overlying the breast, with the assumption being that the temperature will be elevated in skin overlying a cancer. This can be true in the case of larger cancers (several centimetres in diameter) but is much less commonly the case for smaller, often curable tumors; and it is the early discovery of these smaller potentially curable tumors that allows breast screening by mammography to save lives. The NBOCC quotes evidence stating that abnormal thermography imaging occurs in less that 50% of breast cancers found by mammography. That is, it misses over 50% of tumors identified by mammography.)

 

Screening is a woman’s choice - Some facts to help women choose

Almost all doctors and government health authorities in Australia recommend breast cancer screening in women aged 50 to 70 years. Currently the United States Preventive Services Task Force gives screening mammography a ‘B rating’, indicating that it found at least fair evidence that mammography improves important health outcomes and that benefits outweigh harms. It recommends that clinicians offer mammography to suitable patients.

While there is a proven overall benefit for the group of women who choose to be screened, there is no guarantee that any particular woman will benefit and most will not. (But those that do may have their life saved!!) Thus, each woman should make up her mind regarding mammography screening. The answers to the questions below might help women make their choice. (Please remember that the figures mentioned are approximations and are meant act as a general guide.)

 

At present (2019) in Australia about 56% of women in the target range for screening (50 to 69 years) participate in the mammography program.

 

 

1. What is the benefit?

Screening mammograms pick up about 85% of breast cancers present and if all Australian women in the 50 to 70 year age group had regular screening mammograms, death from breast cancer could be reduced by about 30 per cent in this age group. This equates to a reduction in female deaths from breast cancer of about three or four per 1000 women (or one in 333 to one in 250) during the 20 years of screening (i.e. in the 50 to 70 year age group). In the whole population of Australia, this is a large number of women and, very importantly, it is a large number of not old women. If the average age of women in this group who have breast cancer prevented is 61, then on average each woman would gain roughly an extra 25 years of life. (This includes years at the end of life that involve ill health and with this in mind, a better indication of benefit might be that this 25 years has been estimated to equate to about 18 years of healthy normal life.)

 

If you screen 1000 women aged 50 years for 20 years, it is estimated that about 4.3 of those women will have the benefit of avoiding a breast cancer death.

 

Breastscreen Australia states that the program reduces death from breast cancer in this screened group in this 20 year period by betwen 21% and 28%. However, the overall reduction in death from breast cancer due to screening in the screened group is only about 15% because screening does not significantly affect the death rate from breast cancer in women outside the 50 to 70 year breast cancer screening age group.

 

And the advantage provided by screening to the community generally is reduced because only about 56% of women choose to be screened.

 

It is worthwhile pointing out that these are average figures. Women who have a less than average life expectancy will on average gain less benefit from mammography screening. This includes women who either;

Most of these women are still likely to benefit from mammography; it’s just that the benefit will on average be less.

 

 

2. How many women need further investigation following their mammogram?

With regard to initial mammograms, up to 10% will require follow-up and about 1.5% will require breast biopsy. For subsequent mammograms, up to 5% require follow-up and about 1 per cent will require breast biopsy.

The chance of one recall over the whole 20 year period of screening (age 50 to 70 years) is about 40% to 50% and the chance of being advised to have a needle biopsy to aid in the diagnosis of an abnormality found by mammography over the same period is about 10%.

3. What percentage of women who are recalled have cancer?

Overall about 10 per cent of women recalled for investigation are found to have cancer. This rate increases with increasing age as breast cancer rates increase in older women. For women in their 50s, 92% needing further investigation following mammography won’t have cancer. This compares with 88% in their 60’s.

4. What percentage of breast cancers does mammography miss?

Unfortunately, mammography is not perfect and it does not pick up all breast cancers. It will miss a few that are present at the time the woman is screened and some will arise in between mammograms. Thus, women still need to have changes in their breasts investigated by their doctor even if they have had a recent mammogram that was normal. In Australia at present, mammography detects roughly 70% to 75% of the invasive breast cancers diagnosed, with the remainder being found by women during the intervals between mammograms. The mammogram detection rate increases with age.

5. What is the over-diagnosis rate for breast cancers found during mammography screening?

Many of the breast cancers detected by screening mammography are small and some of these would not go on to cause problems as the cancers themselves are not ones that will progress to cause symptoms. It is not known accurately what this rate is, but the best guess is that about 10% to 20% of cancers detected by screening mammography would not have caused symptoms. (Figures from reputable studies vary widely, ranging from 2% to 30%.)

 

Looking again at 1000 women screened for 20 years from the age of 50, it is thought that about 68 cancers will be diagnosed and 13 of these will be cancers would not have caused a problem i.e. were overdiagnosed. (As mentioned above, about 4.3 of these women will avoid death from breast cancer during the screening period because they took part in screening mammography for the 20 years. Many but not all of the other 40.7 women diagnosed with breast cancer from screening will die from their cancer during the screening perioid and after the age of 70 years; although some will die from other conditions.

 

While many cases of over-diagnosis involve ‘ductal carcinoma in situ’ type cancers, some invasive cancers diagnosed by screening mammography would also not have gone on to cause harm.

 

Disadvantages of screening mammography

1. Increased anxiety / stress

As can be seen from above, about 50% of women who have second yearly mammograms from age 50 to 70 years will need recall and about 10% will require biopsy. The majority of these women will not have cancer and will have been worried for no reason. Many women will be able to rationalise this as the price that needs to be paid for increased protection. However, a few will suffer considerably from increased stress due to worry about the abnormal test and while this may be ‘cured’ by having a normal biopsy, some will never be able to remove the thoughts of the risk of breast cancer from their minds. A small group of women will just worry about having the mammograms themselves done.

 

If 1000 women aged 50 years were screened for 10 years, it is thought that about half will be scared unnecessarily because a screening test has found an abnormality that is not significant (i.e. a false alarm) and about 100 will undergo a biopsy unnecessarily.

 

2. Over diagnosis (and subsequent over-treatment) of clinically relevant ductal carcinoma in situ:

Some cancers that are found by screening mammography would never have caused problems; either because they would have stopped developing into cancers or would have grow very slowly and the person would have died of something else before the caucer caused problems.) However, these cancers end up being treated anyway as doctors have no way (yet) of telling which cancers they are.

 

It is thought that If 1000 women aged 50 years were screened for 10 years, somewhere between 4 and 15 will be overdiadnosed and treated for cancers that would never have caused a problem. These women receive therapies that cause harm, including chemotherapy and radiation. The problem is we don't know who they are.

 

The prior discussion about ductal carcinoma in situ mentioned the fact that the introduction of screening mammography has brought with it the diagnosis of many more cases of this disease. There is still considerable uncertainty regarding how much of this disease is clinically significant and it is likely that a significant proportion that is being diagnosed would never have become clinically relevant. As breast cancer is a very serious disease and there is no way of telling which cancers are not significant, all cases need to be treated surgically and some of this surgery will be unnecessary; but no one really knows how much.

 

One finding of a review of breast cancer research by the well-respected Cochrane Centre was that for every woman who has her life prolonged, about 10 will receive unnecessary treatment of some sort. (This included those requiring needle biopsy as well as those requiring surgery.)

 

Over-diagnosis and over-treatment are ‘less’ relevant when screening older women as cancers are more common in this group and thus the benefits of screening are greater.

 

It is also true that a few cases of invasive cancer diagnosed by mammography will not become clinically relevant, either because the disease does not progress or because the person dies beforehand.

3. Inconvenience:

There is a cost in terms of both time and money in having ten mammograms performed and they are uncomfortable and, for some, embarrassing procedures. Biopsy when needed is associated with similar inconvenience.

10 year outcomes for women who are screened and non-screened for breast cancer

 

Results for 1000 women for the 10 years from age 40 to 50

(in number of cases)

Results for 1000 women for the 10 years from age 50 to 60

(in number of cases)

Results for 1000 women for the 10 years from age 60 to 70

(in number of cases)

 

Have biennial screening

DO NOT have any screening

Have biennial screening

DO NOT have any screening

Have biennial screening

DO NOT have any screening

Number recalled for extra tests1

251 (25%)

(60 need a biopsy)

Nil

242

(24%)

(64 need a biopsy)

Nil

185 (

19%)

(56 need a biopsy)

Nil

Invasive breast cancers detected3

17.6

(8.5 by screening and 9.1 interval cancers2)

13.2

28.0

(17.6 by screening and 10.4 interval cancers2)

19.8

32.5

(23.3 by screening and 9.2 interval cancers2)

23.9

Ductal carcinoma in situ4

3.4

0.3

4.9

0.4

5.5

0.5

Total breast cancer diagnosed

21.0

(17.6 + 3.4)

13.5

(13.2 + 0.2)

32.9

(28.0 + 4.9)

20.2

(19.8 + 0.4)

38.0

(32.5 + 5.5)

24.4

(23.9 + 0.5)

Deaths from breast cancer

 

2.0

(2.0 is 20% less than 2.5 deaths in non-screened.)

2.5

4.0

(4.0 is 32% less than 5.9 deaths in non-screened.)

5.9

5.1

(5.1 is 37% less than 8.1 deaths in non-screened.)

8.1

Deaths from all causes

12.8

13.3

29.3

31.1

73.6

76.5

1 The recall rate is about rate is 8.5% for the first screening in the 50 to 70 year age group. For subsequent screenings this rate drops to about 3.9%.

2 Interval cancers are cancers that occur between screening tests.

3 The difference in total number of cancers between respective screened and non-screened groups occurs because screening picks up cancers earlier. Some of the extra cancers picked up in the screened group will become evident in the unscreened group in later years.

4 This is an early stage of breast cancer. Its clinical significance is not yet fully understood and some will probably not cause future problems. They are all still treated. (See other notes in this chapter.)

Source: Aust Fam Physician Vol 35 No ½. Jan/Feb 2006 pp40-1

 

 

Mammography screening will not detect all breast cancers

Women who have regular two yearly screening mammography cannot assume that they will not get breast cancer for two reasons.

  1. Mammography will not pick up all breast cancers present.
  2. Some breast cancers develop in between screening tests; so called interval breast cancers. These cancers tend to be more common in younger women, mainly because cancers tend to grow more quickly in this age group. (At age 40, the number of cancers picked up at mammography screening (about 8.5 per thousand women screened) is about the same as the number of cancers diagnosed in the two year interval between screening mammograms (about 9.1 per thousand women). As breast cancer rates increase with age, the cancer detection rate at screening at age 60 is, as would be expected, much higher at 23.3 per 1000 women. However, the detection rate in between screening (9.2 per 1000 women) has remained about the same as at age 40 and is considerably less than screening pick up rate at age 60.)

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Mammograms in the 40s and over 70s. Are they worth it?

Mass screening for normal risk women aged from 40 to 50 years is not currently recommended in Australia. However, this is a controversial issue and there is evidence that it may be of benefit to normal risk women. About 19 per cent of all breast cancers occur in women aged 40 to 49.

 

Screening women in their 40s will help prevent some extra deaths, with most of this benefit occurring in women in their late 40s.

 

On the other hand there are several good reasons for women not to have mammograms if they are in the 40- to 50-year age group. Firstly, it increases the likelihood of having an unnecessary investigation as there is a higher incidence of false positives in younger women. For women in their 40s, 96% needing further investigation following mammography won’t have cancer. This compares with 92% in their 50’s and 88% in their 60’s. This higher incidence of false positive tests also causes additional unnecessary anxiety.

 

There is also an increased rate of false negative tests (i.e. missed cancers) in younger women as screening is less sensitive in pre-menopausal women due to their denser breast tissue. The inconvenience and discomfort of the procedure and the extra expense to the community are also issues to consider.

 

Mass screening of women over 70 years of age is also not recommended at present. However, the benefit is about the same as screening the 40 to 49 year age group and thus it is reasonable for women over 70 to continue their screening program if they so wish. The gradually increasing life expectancy of women may also be a factor in the decision to extend screening mammography into the 70s. (This is of course assuming that this trend continues, a fact that is not at all certain considering the present epidemic of obesity and physical inactivity.) A comparison of the benefits for screening at different ages is shown in the table above.

 

Breast implants & cancer

Breast cancer is no more common in women with breast implants and the prognosis is no worse. Mammograms are, however, not as reliable in women with implants as some breast tissue can’t be visualised.

 

 

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Inherited breast cancer

As stated previously, in a small percentage of cases (less than 5% of breast cancers), cancerous gene changes are ‘handed down’ from parents (i.e. inherited). Inherited genetic mutations can be from the woman’s father or mother, so it is important to look for breast cancer in both sides of the family, including breast cancer in males. The factors that increase the risk of having inherited breast cancer are listed at the beginning of this section.

 

While most women with a family history of breast cancer will not develop the disease, all women with any family history should discuss the matter with their general practitioner so that they can determine whether they need to seek further help in the form of genetic counselling. (See notes on genetic testing below.)

 

Women who do have an increased risk of breast cancer need to be offered additional preventative interventions, which may include more frequent clinical assessment and  mammography, surgery and perhaps treatment with medications such as tamoxifen (This drug is used to treat breast cancer in Australia and overseas it is also used as a preventative treatment for high risk women. It is not used for this purpose in Australia as there are significant side effects such as hot flushes and an increase in DVTs and endometrial cancer.

 

As well as abnormalities in breast cancer genes (discussed below) there are some very rare genetic abnormalities that increase breast cancer risk, such as Li Fraumeni, Lynch and Peutz-Jeghers syndromes. 

Breast cancer genes

There are thought to be many genes that are responsible for hereditary breast cancer but, at present, only a few of these genes have been identified. The two main inherited abnormal genes are the BRCA-1 gene and the BRCA-2 gene, both of which occur in about 1 in 1,000 people. (The rate for both is about 1 in 100 in people of Ashkenazi Jewish descent.). Together, they cause about 20% to 30% of hereditary breast cancer. In normal people these genes act to prevent breast cancer (i.e. they are tumor suppressor genes). People born with faults in these genes do not benefit from this protective effect as much and have a greater risk of the disease. Together, these mutated (genetically altered) genes are responsible for about one to five per cent of breast cancers and are also associated with an increased risk of ovarian cancer. Women with the BRCA-1 gene have about a 60 per cent chance of developing breast cancer by age 70 and a 40 per cent chance of developing ovarian cancer by age 70. The BRCA-2 gene is associated with about a 50% chance of developing breast cancer by age 70 and a 20% chance of developing ovarian cancer by age 70 and an increased risk (up to 10%) of early-onset prostate, male breast, and pancreatic cancers and melanoma. (Remember that these gene changes are also carried by males.

 

Tumour Suppressor Gene ‘Tp53’ is another rarer genetic mutation (1 in 10,000) that can cause an increased risk of breast cancer and several other cancers (mainly bone and soft tissue cancers).

 

Women diagnosed with these genetic abnormalities have access to Medicare-funded MRI breast cancer screening, which is superior to standard mammography screening in this group.

 

Possible treatment options for women who caary these genes and are thus at very high risk of breast cancer include prophylactic bilateral mastectomy, removal of both ovaries or preventative hormone therapies.

 

Tumour Suppressor Gene ‘Tp53’ is another rarer genetic mutation (1 in 10,000) that can cause an increased risk of breast cancer and several other cancers (mainly bone and soft tissue cancers).

Genetic testing for breast cancer genes

Genetic testing is currently available in Australia for determining changes in the BRCA1 and BRCA2 genes. (Tp53 testing is also possible.) It is only offered to high risk women and is inappropriate for low risk individuals as it is very unlikely to provide any helpful information and is likely to give false reassurance. In a high risk family, the individual first tested is almost always one who has had breast cancer. Initial testing is seldom offered to unaffected individuals.

It is important to realise that genetic testing is not perfect. A significant number of people possessing BRCA-1 and BRCA-2 changes will be missed and there may well be other inherited genes responsible for breast cancer that are as yet unknown and can not be tested for. Thus, an important limitation of these genetic tests is that a test that does not find an abnormality may be giving false reassurance to the tested person and other family members.

Genetic testing (done by taking a blood sample) should only be done after thorough counselling that includes discussion of all management options and the consequences for the woman and other members of her family of diagnosing a harmful genetic abnormality. Such problems include fear and anxiety for themselves and their children, family planning issues, and disruption of immediate and broader family relationships. It is also important to understand that, as most cases are complex and the current understanding of the genetics of breast cancer is far from complete, exact assessment of risk is difficult to achieve; and risk is a relative thing. What is an acceptable risk for one person is not for another. Thus, it is often difficult for doctors to give specific advice about what treatment options patients should choose. For the above reasons, genetic testing should be done by experts in the field. A good option is using Family Cancer Clinics. Information about them can be found on the Cancer Council Australia website; Women can ask their GP for a referral to these clinics.

 

Further information

Caner Australia - Breast Cancer section

https://canceraustralia.gov.au/affected-cancer/cancer-types/breast-cancer

 

Breast Screen Australia

http://www.cancerscreening.gov.au/internet/screening/publishing.nsf/Content/breast-screening-1

Ph 13 20 50

 

Australian Screening Mammography Decision Aid Trial
http://www.mammogram.med.usyd.edu.au

(An aid, which is being presently trialled, which helps in deciding whether to have a mammogram in the 40 to 49 year age group.)

 

 

NSW Cancer Institute

https://www.cancerinstitute.org.au

 

 

 

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