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Research has uncovered many of the risk factors associated with this common cancer. By identifying the risk factors, we are closer to finding the cause of breast cancer and also by modifying these risk factors, we can reduce our risk. This is the first strategy to combat breast cancer namely prevention or eradication of the cancer. However, this objective is difficult to achieve as some of the risk factors cannot be modified e.g. family history, or lifestyle factors such as child bearing. Despite the intensive search for the cause of breast cancer, the exact cause of breast cancer remains unknown. About 50% of our breast cancer patients have no identifiable risk factors.
They can be grouped into the following:
- Age & Sex
- Family History
- Factors Associated with Reproductive History of a Woman
- Dietary Risk Factors
- Body Weight and Physical Activity
- Intake of Hormones
- Previous Abnormal Breast Biopsy
1. Age & Sex
The risk of breast cancer increases with age. It is uncommon in a woman before 40 years old. 70% of all breast cancers are diagnosed in women 40 years of age and older.
Breast cancer can also affect the male but the risk is very low compared to the female. However, when a breast cancer is diagnosed in a male it is often at an advanced stage because of the small size of the male breast.
2. Family History
A woman with this risk factor has a first degree relative (i.e. sister, mother or maternal grandmother) with breast cancer. Her risk is doubled (2X) when compared to a woman without this risk factor. (See “How to estimate one’s risk from breast cancer?”) However, family history is not a significant risk factor as only 10% of breast cancer patients have it. Our recommendation for woman with this risk factor is to start breast screening at an earlier age at approximately 35 years old.
This risk factor comes from the inheritance of genes from our parents and ancestors. Genes contain encoded information and are stored in our cells and passed on from generation to generation. The information contained in our genes is needed for the normal function of our cells. When our genes are damaged, cell function becomes abnormal and a cancer may be formed.
We have identified certain genes, which may be responsible for breast cancer. Inheritance of abnormal forms of such genes increases a woman’s chance of getting breast cancer. Two such genes recently identified are BRCA1 and BRCA2 genes and inheritance of abnormal copies of either of such genes increase a woman’s risk by several fold! Such a woman will have a 40 to 60% of developing breast cancer in her lifetime.
Tests to detect such abnormal genes are at present difficult and performed mostly in research laboratories. If you are interested in such tests, you should consult your doctor. There are laboratories in Australia and America, which offer this service.
There is another way to identify a woman with these abnormal genes (BRCA1 and/or BRCA2). Her family history is more extensive and stronger with the following features:
- Many relatives developing breast cancer at an early age (< 40 years).
- Woman who develop breast cancer in both breasts at the same time (i.e. bilateral).
- More than two generations of relatives with breast cancer.
- Relatives with cancer of the ovary.
- Fortunately, such women only form a small proportion of women with breast cancer, estimated at only 1%. A big controversy surrounds the management of such women and most of the cancer centers at our major hospitals have special departments to cater to them.
How to estimate one’s risk of breast cancer
The most important risk estimate is the absolute risk i.e. the risk of developing breast cancer in one’s lifetime. For a Caucasian woman in America, this risk is about 12%. As breast cancer is less common in Singapore women, the lifetime risk is about 5% i.e. the chance of a Singapore woman developing breast cancer in her lifetime is about 5%.
Doctors often quote another risk estimate called the relative risk. For example, a woman with a family history of breast cancer has relative risk of 2.0 i.e. her risk is doubled compared to a woman without this risk factor. Her absolute risk becomes 10% (2 x 5%).vessels and to help to drain fluid from the body back into the blood circulation. An important function of the lymphatic system is the protection of the body against foreign invasion e.g. bacteria or other micro-organism. These foreign bodies are destroyed in lymphatic glands (called lymph nodes) which are situated in certain parts of the body such as the neck, armpits and groin. |
3. Factors Associated with The Reproductive History of a Woman
Research has identified certain aspects of a woman’s reproductive history that can increase her risk from breast cancer. These risk factors are:
- Woman with no children or having the first child late
(after 35 years old)
- Early onset of menses (earlier than 11 years old)
- Late cessation of menses (later than 55 years old)
These risk factors are associated with an early and prolonged exposure to oestrogen, which is one of the female sex hormone.
A woman attempting to modify these risk factors to reduce her risk from breast cancer will find it difficult to do so as it could mean substantial alterations in her lifestyle. There are calls in America to make changes in colleges and the work place to facilitate a woman’s wish to have children early. Another measure that is being considered is to encourage young girls to exercise more, as it is known that physical activity can delay the onset of menses and suppress the secretion of oestrogen.
Can breast-feeding alter this exposure of oestrogen and hence reduce a woman’s risk? Yes, but only if the period of breast-feeding is prolonged (e.g. > a year).
4. Dietary Risk Factors
It has been known for a long time that eating too much red meat and animal fat and too little fibre (vegetables & fruits) may increase a woman’s risk of breast cancer. Recent research has failed to prove this conclusively and controversy still surrounds the role of diet as a risk factor. However, Health Authorities such as the National Institute of Health and American Cancer Society recommend limiting intake of saturated animal fats (less than 20% daily fat allowance) and increasing intake of fruits and vegetables (5 servings daily) to reduce our risks from cardiovascular disease and cancer especially breast, colon and prostate cancer.
There is less controversy regarding alcohol as a risk factor for breast cancer. Studies have shown that drinking 1 to 2 glasses of alcohol daily can increase a woman’s risk (relative risk 1.5 times)
Other nutrients that have been identified to alter a woman’s risk from breast cancer are:
- Soy products as in tauhoo, soya bean juice have been shown in studies to reduce a woman’s risk from breast cancer. This may explain why Asian women have a lower risk from breast cancer compared to American women.
- Omega 3 oil found in fish. Some studies showed that it could reduce a woman’s risk from breast cancer.
- Other nutrients that have been found to be protective against breast cancer are vitamin A, selenium, vitamin C & E.
5. Body Weight and Physical Activity
Weight gain especially in postmenopausal women is associated with an increased risk from breast cancer. This can be a combination of high calories and fat intake as well as a lack of exercise. Some Europeans studies have correlated physical activity to the risk of breast cancer. Physical exercise reduces a woman’s risk of breast cancer by lowering her body’s level of oestrogen.
A woman should engage in regular physical activities and moderate her calories and fat intake and avoid weight gain. Her weight should not be more than 20% above her ideal weight.
6. Intake of Hormones
There are 2 periods in a woman’s life that she wants to take oestrogen (± progesterone) supplement:
- Hormone Replacement Therapy (HRT). A postmenopausal woman has a choice of taking HRT or not. There are PROS and CONS of such a choice and this is not the forum for such a controversial topic. Recent studies from America have shown that long term or current users of HRT have an increased risk of breast cancer (up by 30%) and this risk disappear 3 to 5 years after stopping HRT. A woman should enter into a close discussion with her doctor/doctors before making a decision.
- Oral Contraceptive Pill (OCP). The Pill is a popular form of birth control and the worry was whether it would increase a woman’s risk of breast cancer. The conclusion from all the many studies performed is that there is little or no increased risk from taking the oral contraceptive pill. Only a small subgroup of woman may be at a higher risk – early and prolonged usage of the OCP (i.e. late teens, more than 10 to 15 years).
7. Previous Abnormal Breast Biopsy
A woman with a previous breast cancer is at an increased risk of developing cancer of her opposite breast. She should be on regular reviews with her doctor.
A few types of breast biopsies are known to have an increased risk of breast cancer, namely: atypical ductal hyperplasia, atypical lobular hyperplasia and lobular carcinoma in-situ. Woman with such breast biopsy reports should have regular screening starting from her mid thirties.
What can I do if I am at a high risk?
Doctors can now give a fairly good estimate of a woman’s risk from breast cancer by taking a detailed family, social and medical history.
Women who are at high risk from breast cancer will be offered counselling as to how to cope with this knowledge:
- They are offered breast screening at an earlier age.
- They are advised on means to alter their lifestyle and diet to reduce their risk.
- A recent study from America has shown that tamoxifen, an important anticancer drug can significantly reduce the risk of breast cancer in these women.
- These women can consider preventive prophylactic mastectomies as a means to reduce their risk from breast cancer. A recent study from America has shown that high-risk women who underwent bilateral mastectomies have a 90% reduction in their risk. After removal of the breast, it is reconstructed using a woman’s own body tissue or an implant. Because of the psychological consequence and extensive nature of the surgery involved, a woman must consider very carefully this option before deciding on it.
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