There are several known risk factors for developing breast cancer, yet most women who develop breast cancer have no known risk factors other than the fact that they are women. Besides being female, other risks are discussed below.

Age

The chances of developing breast cancer increase with age. Breast cancer is pretty rare before menopause. Four out of five breast cancers occur in women over 50. In fact, the longer you live, the greater your chances are of getting breast cancer. If you reach age 85, your chances of having breast cancer are around one in eight.

Race

Caucasian women are at increased risk of developing breast cancer compared to other racial groups. However, black women are more likely to die from the disease because their cancers tend to be at a more advanced stage when detected. This may be due to a tendency of black women to have more aggressive tumors or it may have more to do with socioeconomic factors.

Low socioeconomic status

Women of all races who are below the poverty line are much more likely to die from their breast tumors than women with higher incomes. This is undoubtedly related to the fact that many of these women lack health insurance coverage and so are much less likely to participate in routine breast cancer screening and also much more likely to put off a visit to the doctor even when they experience early breast cancer symptoms. This means their cancer will tend to be discovered in a later stage when the prognosis is much poorer.

Family history

If your mother, sister, or daughter has had breast cancer, or you have a male relative with breast cancer, you have a greater risk of developing breast cancer. In general, the more relatives you have with breast cancer, the higher your chances of developing the disease. If any family member had breast cancer at a young age (before age 40), the risk is even higher.

Personal history

If you have had breast cancer before, you are at increased risk of having it again. Also, if you’ve had breast cancer in one breast, you have a greater chance of developing cancer in the other breast.

Genetic predisposition

Current research suggests that between 5 and 10 percent of breast cancers are inherited. Two known genes can be inherited (called BRCA1 and BRCA2) that confer an increased risk of both breast and ovarian cancer. These genes normally function to put the brakes on cell division but when an abnormal version of either gene is inherited; your cells are not as effective at preventing out-of-control cell growth, which can lead to cancer. Other genes also confer an increased risk of developing breast cancer but the BRCA genes are by far the biggest known genetic risk factors.

Obesity

Carrying excess weight increases your risk of breast cancer, especially if that weight was gained during adolescence or after menopause. The risk is also more pronounced if you carry the weight in upper body fat.

Radiation exposure

If you had exposure to radiation as a child or young adult, such as through radiation treatments of the chest, it increases your risk for breast cancer. This risk is greatest if the radiation exposure happened during adolescence, when your breasts were developing.

Early menarche or delayed menopause

If you had early onset of your menstrual period, meaning you started your period before age 12, your risk of breast cancer is increased. The proposed reason for this risk is that higher than normal levels of estrogen both trigger early menstruation and increase the risk of breast cancer. Also, if you experienced menopause later than usual, after age 55, you are more likely to develop breast cancer. Again, estrogen levels are thought to be to blame. In this case, having the high levels of estrogen that are present during the fertile period for longer than normal causes breast tissue to divide more often, increasing cancer risk.

Late first pregnancy

If you do not have a full-term pregnancy until age 30 or if you never become pregnant, your risk of breast cancer increases. Researchers don’t really understand why but becoming pregnant - and the breast development that ensues - somehow seems to protect against genetic mutations. One possibility is that pregnancy changes the way that the breasts respond to estrogen in the future and reduces the risk that estrogen-induced cell division in the breast will cause cancer.

Hormone replacement therapy (HRT)

During menopause, body levels of the hormones estrogen and progesterone decline to much lower levels than during the fertile period. Perimenopausal and postmenopausal women often experience unpleasant symptoms (such as hot flashes) during the time that their hormone levels are changing and other symptoms thereafter, including memory impairment. HRT involves taking doses of estrogen (sometimes with progesterone) to replace the lost hormones and prevent these unpleasant symptoms from occurring. Taking HRT for four or more years increases the risk of breast cancer, perhaps because estrogen increases the rate of cell division in breast tissue. In addition, HRT is associated with abnormal findings on mammography that may make it more difficult to see a cancerous focus.

Birth control pills

Using birth control pills appears to be a mild risk factor for breast cancer. The risk seems to be largest when the pill is taken for four years or more before a first pregnancy and tends to increase the risk for developing cancer before menopause. Although there is some debate about how long the risk of cancer is elevated, the increased risk may go away after 10 years of not taking the pill. New research on this topic is published often so check the news for updates (See: Recent Developments in Breast Cancer).

Alcohol use

Drinking alcohol appears to increase the risk of breast cancer and the effect seems to occur at surprisingly low levels of alcohol consumption. According to the American Cancer Society, having more than one drink a day can increase the risk of breast cancer by 20 percent. However, other studies have shown that moderate levels of alcohol consumption may cut the risk of heart disease, so one drink a day may be alright. Talk to your doctor to find out more about alcohol consumption and disease risk.

Precancerous conditions

If you have a precancerous breast condition that is caused by an increased rate of cell division in the breast, it increases your risk of developing breast cancer. Examples include atypical hyperplasia and ductal carcinoma in situ. These benign conditions can only be diagnosed through biopsy but if you have one of the precancerous conditions, you and your doctor should work out a plan for monitoring the condition.

“Dense” breasts

Having breasts that are dense means they have relatively more connective and glandular tissue than fat. This makes it more difficult to see cancerous changes on a mammogram. In addition, dense breasts may also have an inherently higher risk of developing cancer, though the risk appears to be small. The reason why women with more dense breasts have increased breast cancer risk is unknown.