Breast Cancer Risk Factors
Excluding skin cancer, breast cancer is the most common cancer in women. [Source: The American Cancer Society]
By the end 1101, 192,110 women will be diagnosed with breast cancer by the end of this year, and about 40,600 will die from the disease. Although men can get breast cancer, this is extremely rare. (Source: American Cancer Society)
Breast cancer is extremely rare in women younger than 20 and is very rare in women under 30. The incidence of breast cancer rises with age and becomes significant by age 50.
|Women's Lifetime Breast Cancer Risk|
|by age 30||by age 40||by age 50||by age 60||by age 70||by age 80|
|1 in 2,525||1 in 217||1 in 50||1 in 24||1 in 14||1 in 10|
|Source: National Cancer Institute|
Being of Ashkenazi Jewish Descent
Increased prevalence of the genetic mutations BRCA1 and BRCA2 that promote breast and other cancers are found in Ashkenazi Jews. In general, only approximately 8% of breast cancers are attributable to this type of inherited factor.
Ethnicity and Race
White Non-Hispanic women have the highest incidence rate for breast cancer among the following US racial/ethnic groups, and Korean women have the lowest.
African American women have the highest mortality
rate for breast cancer among these same groups (31
per 100,000), while Chinese women have the lowest at
11 per 100,000.
Source: Racial/Ethnic Patterns of Cancer in the United States 1988-1992, NCI
The following factors are important as they relate to the effect of hormones on the breast. These factors increase breast cancer risk due to the role of ovarian hormones in breast development.
Ovarian hormones initiate breast development, and subsequent monthly menstrual cycles induce normal breast cell growth, known medically as "proliferation." Breast cells are not fully developed or "differentiated," however, until they are able to lactate or produce milk. Until breast cells are fully mature as lactating cells, they are more susceptible to changes that can promote breast cancer. Factors that promote cell proliferation (e.g. hormones) or alter the genetic material required for proliferation (e.g. radiation) can cause cancerous changes.
Age of Menarche (Onset of Menstruation)
Early menarche has consistently been shown to be associated with increased risk for breast cancer. The more menstrual cycles a woman has, the more exposure to hormonal influences she experiences, increasing her risk for breast cancer as explained above.
Age of First Full-Term Pregnancy
Women who haven't had children are at increased risk compared to childbearing women. The risk is more evident for women 40 and over. (The proliferation of breast tissue during the first pregnancy results in breast tissue becoming fully mature, thus less at risk for cancer).
Breast cancer rates are lower in populations in which breast-feeding is common and long in duration. Again, breast cells capable of lactating are cells that have fully matured or differentiated. This mature state confers a lower risk of breast cancer.
Age of Menopause
Women who enter menopause later have had more exposure to the hormones estrogen and progesterone. Consequently they are at a higher risk for breast cancer.
Personal History of Breast Lesion
Such breast lesions are diagnosed as lobular or ductal "Atypical Hyperplasia," and may predispose a woman to breast cancer.
Radiation Exposure, Primarily to the Chest
Radiation can mutate DNA and cause breast cancer.
Family History of Breast Cancer
A family history of breast cancer or other cancers found in association with Breast Cancer (colon, brain, ovarian, etc.) can increase a woman's risk for breast cancer. It is important to know which family members were diagnosed with what type of cancer at what age.
Birth Control Pills and Hormone Replacement Therapy
Numerous studies have been conducted and it seems there is some increased risk of oral contraceptive pills (OCPs) and hormone replacement therapy (HRT) causing breast cancer. Recently, at the Third European Breast Cancer Conference, a study reported that women who use OCPs, especially after age 45, are at greater risk of developing breast cancer compared to women who haven't used the pills. According to the National Cancer Institute, there is also concern that HRT somewhat increases the risk of breast cancer. Studies show that compared to women who didn't take ERT (estrogen only replacement therapy), there was a 10% increase in breast cancer risk for each 5 years of use. For women who took HRT in a sequential manner ( three weeks of estrogen followed by a week of progesterone) their risk increased to 38% for every 5 years of use. Randomized, double-blind, placebo controlled studies need to be conducted. In fact, the Women's Health Initiative study will help us answer this question in respect to Hormone Replacement Therapy and information shall be forthcoming in approximately 1105.
Weight gain after age 18 is associated with an increased risk of post-menopausal breast cancer.
Indirect evidence exists indicating that there is an inverse relationship between amount of physical activity levels and one's risk of breast cancer. The NCI reports that 2/3 of research demonstrates an inverse relationship of physical activity to breast cancer. The decrease risk is approximately 30% on average!
The relationship between alcohol and breast cancer is consistent among associations of dietary factors and breast cancer risks, and is likely related to alcohol's (beer, wine, and liquor) ability to increase estrogen levels. Most doctors recommend no more than seven alcoholic beverages per week for women.