Established Risk Factors
Keeping all these in mind, the following briefly describes the established risk factors:
Breast cancer is almost an exclusive disease of the female. Being female is the single most important risk factor.
An increasing age is associated with an increased risk. Breast cancer is extremely rare before the age of 25 years.
Where you live is important. Breast cancer is more common in western countries compared to Asian and African countries. (See Breast Cancer – A serious problem)
A previous history of breast cancer
If you have had breast cancer of one breast before, you now have 4 times the risk of developing breast cancer in the opposite breast.
A family history of breast cancer & genetic risks
A woman with a mother or sister (first degree relative) who develops breast cancer at a young age, has twice the risk of developing breast cancer herself, and this risk increases to 4 times if 2 first-degree relatives are affected.
For men, he is at higher risk if his father or brother or son has had breast cancer. Female relatives of men with breast cancer often have an increased risk of breast cancer. In some reports, 60% of men with breast cancer have female relatives with breast cancer.
It is important to know how old they were at the time they were diagnosed.
Only 5-10% of women with breast cancer have a genetic defect. In 1990, the BRCA1 gene was discovered, and this was followed a few years later by the discovery of the BRCA2 gene. The presence of either gene is associated with an 85% chance of developing breast cancer by the age of 65 years. The BRCA1 gene is also associated with a risk of ovarian cancer. It is not an extra gene but a defective or mutated gene that promotes growth of breast cancer.
Families of women with BRCA1 often have a history of several generations of women suffering from early onset and even bilateral breast cancer (affecting both breasts). However, they have also discovered women with BRCA1 gene that did not have family members with breast cancer.
A rare form of inherited breast cancer, Li-Fraumeni syndrome has been linked to mutation in the gene p53. Breast cancer in these patients is also associated with tumours of the soft tissues, bones, brain and adrenal gland.
A history of benign breast disease
The term “benign breast disease” covers many types of cellular abnormalities. Women with atypical hyperplasia, a type of benign breast disease where the cells are mildly abnormal, have a 4-fold risk of developing breast cancer. A history of fibrocystic disease or proliferative disease may carry a very slight increased risk as well.
Early menarche (onset of menstruation) before the age of 12 years old, and late menopause (cessation of menstruation) after the age of 55 years are associated with a 2-3 times increased risk of breast cancer. This is related to the cumulative number of ovulatory cycles, and it is thought that the prolonged exposure to oestrogens may play a role is the causation of breast cancer.
Nulliparity (never having borne children) or late age at first childbirth (after the age of 30 years) increases the risk of breast cancer. This is probably related to the number of uninterrupted menstrual cycles.
Exposure to ionising radiation
Exposure to ionising radiation eg xrays, particularly between the age of puberty and 30 years, can substantially increase the risk of breast cancer. However, exposure to significant levels of radiation that are clinically important is rare.
Previous exposure to atomic bomb explosion will have a 3-fold risk of developing breast cancer compared to the person without such exposure. Radiation risk is estimated from data derived from high-dose exposures, such as in survivors of atomic bomb attacks, uranium miners, people exposed to radon gas, tuberculosis patients who have undergone multiple fluoroscopic procedures (a practice that is no longer done for many years), and patients who receive radiation treatment for post partum mastitis and Hodgkin’s disease. The radiation doses in these settings have ranged from 250mGy-20Gy (25 to 2000 rads) which are doses way above those received in the usual x-rays taken for diagnostic purposes.
Women of higher socio-economic status are at greater risk of breast cancer compared to women of lower socio-economic status. This reflects differing reproductive patterns such as age at menarche, age at menopause, age at first childbirth and also diet.
The composition of the diet has been thought to influence the risk of breast cancer, and may account for the differences in incidence rates between countries. However, only weak or non-existent associations have been found in case-control studies. There is also some evidence that alcohol consumption results in a slight increase in risk of 1.4 to 2.0.
Obesity in postmenopausal women is associated with an increased risk of breast cancer. This is because oestrogens can be produced in fat; hence postmenopausal obese women have higher levels of circulating oestrogens, and as mentioned before, breast cancer is associated with increased oestrogen exposure.
Oral contraceptives (OCP) and hormone replacement therapy (HRT).
Prolonged oral contraceptive usage is associated with breast cancer diagnosed in premenopausal women; however the risk is only around 1.2 times.
Hormone replacement therapy is currently commonly prescribed for postmenopausal women as it prevents osteoporosis and may protect the heart. A combination of oestrogens and progestogens are used. The dose of oestrogens prescribed is very low, and the risk of breast cancer increases only after more than 5 years’ usage, and even then the risk of developing a tumour with favourable prognosis is about 1.8 times compared to those who never used HRT.
Amongst women who have used HRT for more than 5 years, the relative risk is about 2.6.
The latest updated analysis of the Women’s Health Initiative (WHI) randomised trials have found that the combined estrogen plus progestin therapy doubles a woman’s risk of death from breast cancer, nearly doubles the risk of death from non-small cell lung cancer and increases the risk of death from colorectal cancer by 54%. The combined HRT also appears to increase the incidence of all subtypes of breast cancers, not just the estrogen-receptor positive breast cancers but also those which where estrogen-receptor negative, triple-negative, HER2-overexpressing as well as HER2-negative cancers.
The decision for women to begin HRT is dependent on many factors. HRT helps to improve the hot flushes, mood swings and other menopausal symptoms that can be severe in some women. The risk/benefit ratio requires careful consideration before HRT is used. Should HRT be needed because menopausal symptoms cannot be managed by other means, then, the duration of HRT intake should be as short as possible.
Large studies have found no association between breast-feeding and breast cancer. Breast feeding does not appear to confer a protective effect either although in 1999, data from the Carolina Breast Cancer Study suggests that breast feeding is associated with a slight reduction in the risk of breast cancer among both younger and older (childbearing) women. Still the authors caution that since the study results conflicts with previous studies, it is premature to advise women to breastfeed solely to reduce their breast cancer risk. Breastfeeding should be promoted because of its myriad benefits to both baby and mother.