How Does Breast Size Affect Breast Cancer?

Separating Medical Fact From Urban Myth

It may stand to reason that larger breasts place a woman at greater risk of breast cancer due to, well, the very size of them. At the very least, one might assume that finding a lump would be harder if you wear a triple-D cup compared to someone who wears, say, an A cup.

But is this a medical fact or just an urban myth?

Nurse evaluating mammogram results
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Breast Size and Body Weight in Relation to Breast Cancer

The simple truth is that there have been no large, peer-reviewed studies that support breast size as a factor in the development of breast cancer. While there has been some research suggesting a link, there have been just as many which have drawn the opposite conclusion.

With that being said, we do know that obesity plays a significant role in the development of breast cancer and that obese women typically have larger breasts than the average woman. So while this might suggest that big-breasted women are at risk, it appears that weight is more of a factor than actual breast size.

Factors in Assessing Breast Cancer Risk

Beyond weight, there are key factors you should consider when assessing your personal breast cancer risk:

Family and Personal History

Having a mother, sister, or daughter with breast cancer doubles your risk right off the bat. Moreover, the risk only increases if your first-degree relative was young. If there are more than two such relatives, your risk triples and even quadruples.

But does that mean women with no familial history of cancer are free and clear? According to breast cancer research, that is not the case. In fact, less than 15% of women diagnose with breast cancer have a family member who has been diagnosed as well. 

Alcohol Consumption

Women who drink alcohol increase their breast cancer risk. And the more a woman drinks, the higher the risk goes. In fact, research has shown that women who drink as little as three drinks per week have a 15% higher risk of breast cancer when compared to women who consume no alcohol at all.

As an independent risk factor, alcohol is known to increase the levels of estrogen and other hormones associated with the development of breast cancer. Heavy alcohol use can also directly damage DNA in the cells of breast tissue. Damage like this can cause cells to multiply abnormally and at a heightened rate, giving rise to precancerous and cancerous tumors.

Genetic Risk Factors

Genetics may play a role in up to 10% of women diagnosed with breast cancer. This occurs when a mutated gene has been passed down from a parent, including the father. The most common mutations associated with breast cancer are BRCA1 and BRCA2.

If genetic testing indicates that a woman is a carrier of these mutated genes, she is at an increased risk for the development of breast cancer and will typically require more frequent monitoring than other women.

One in 40 women of Ashkenazi-Jewish heritage have the BRCA gene mutation, which means of those that have the gene mutation about 50% of them will get breast cancer by the time they turn 70. By contrast, only 7 out of 100 women in the general U.S. population will get breast cancer.

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7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Eriksson N, Benton GM, Do CB, et al. Genetic variants associated with breast size also influence breast cancer risk. BMC Med Genet. 2012;13:53. doi:10.1186/1471-2350-13-53

  2. Cleary MP, Grossmann ME. Minireview: Obesity and breast cancer: the estrogen connection. Endocrinology. 2009;150(6):2537-42. doi:10.1210/en.2009-0070

  3. U.S. Breast Cancer Statistics. Published February 13, 2019.

  4. Drinking Alcohol. Published August 30, 2016. 

  5. Abraham J, Balbo S, Crabb D, Brooks PJ. Alcohol metabolism in human cells causes DNA damage and activates the Fanconi anemia-breast cancer susceptibility (FA-BRCA) DNA damage response network. Alcohol Clin Exp Res. 2011;35(12):2113-20. doi:10.1111/j.1530-0277.2011.01563.x

  6. Hereditary Breast Cancer and BRCA Genes. Centers for Disease Control and Prevention. Published April 5, 2019

  7. Jewish Women and BRCA Gene Mutations. Centers for Disease Control and Prevention. Published April 5, 2019

Additional Reading
  • Centers for Disease Control and Prevention (CDC). “What Are the Risk Factors for Breast Cancer?” Atlanta, Georgia; updated April 4, 2016.

  • National Cancer Institute. "BRCA1 and BRCA2: Cancer Risk and Genetic Testing." Washington, D.C.; May 29, 2009.