Breast cancer is the most common cancer affecting American women, with over 200,000 new cases per year and 40,000 deaths. According to the American Cancer Society, one in eight women in the U.S. will suffer from breast cancer in her lifetime--a 12 percent risk. And that risk increases based on certain factors, such as lifestyle, genetics, and family history. So if a woman has breast cancer, her sisters are at increased risk.
Family History Risks
Other than genetic risk--carrying the BRCA1 or BRCA2 gene--having an immediate relative who has suffered from breast cancer is the leading hereditary risk factor for contracting the disease. A woman with one first-degree relative--a mother, daughter or sister--with breast cancer faces twice the normal risk. Having two first-degree relatives increases her risk five times the norm. In addition, that risk increases if her sister was under 50 when she got breast cancer. The younger a woman's sister was when she contracted breast cancer, the greater the woman's own risk.
Although 20 to 30 percent of all women with breast cancer do have a family member with the disease, it is important to recognize that the majority of women--70 to 80 percent--do not have a family history. Having a sister with the disease does increase a woman's chances to 24 percent, or one in four--but it does not make it a certainty that she will contract breast cancer.
Genetic Risks
Simply having two or more cases of breast cancer within one family does not mean the cases are related; such a determination requires a genetic analysis of all cases in past and present generations. Since breast cancer strikes one in eight women, it is likely that more than one woman in a large family will be affected.
Breast cancer families are families in which three or more first-degree relatives have been diagnosed with breast cancer. According to Dr. Barbour Warren of Cornell University, women in these families are at high risk of developing breast cancer at a young age, often in both breasts. In breast cancer families with many cases, the BRCA gene is present as often as 87 percent of the time; in those families with relatively few cases, the gene is present 15 to 20 percent of the time. Women with the BRCA gene make up approximately 20 percent of all women with a family history and face a 37 to 68 percent lifetime risk for breast cancer. The risk for women without the BRCA gene is dependent upon their age and number of relatives with breast cancer.
Contributing Risks
The most likely explanation for why some women from breast cancer families develop cancer while others do not lies in lifestyle and environmental factors, such as age at first child's birth. A study of 230,000 women by Harvard Medical School and Brigham and Women's Hospital found that women with a family history who ate five servings of fruit or vegetables each day decreased their risk for breast cancer by 71 percent, while those women without a family history showed no decrease in their risk. This study also showed decreased risk when carotene-rich foods--carrots, sweet potatoes, broccoli--were included in the diet, and when women breastfed their babies or engaged in strenuous activity as young adults. Conversely, their risks for breast cancer increased with alcohol consumption.
References
- American Cancer Society: What Are The Risk Factors For Breast Cancer?
- Cornell University: Program on Breast Cancer and Environmental Risk Factors
- Health News: Family History of Breast Cancer Raises Risks
- BreastCancer.org: March 2008: Breast Cancer Risk and Your Family
- Brigham and Women's Hospital: Nurses' Health Study
