Breastfeeding Found to Reduce the Risk of Triple Negative Breast Cancer in Women Under Age 50

FREMONT, CA (January 22, 2018) — Triple negative breast cancer (TNBC) is an aggressive subtype with few known risk factors. In a study led by the Cancer Prevention Institute of California and epublished ahead of print on January 13 in the International Journal of Cancer, researchers found that women under the age of 50 who breastfed for at least 24 months over their lifetime had a lower risk of developing TNBC. For women with three or more full-term pregnancies, risk increased two-fold if they did not breastfeed or only did so for less than a year. No increase in risk was seen for women who breast-fed for more than a year.  

These findings suggest that breastfeeding may mitigate the elevated TNBC risk associated with pregnancies in younger women. None of these associations were observed among women age 50 or older. 

TNBC breast cancer lacks expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor. This type of breast cancer has the worst prognosis and lacks targeted treatment. TNBC is more common among African Americans, Hispanics and younger women. About 12% of all invasive breast cancers are diagnosed as TNBC.
According to Esther M. John Ph.D., M.S.P.H., the lead researcher of the study, “Our finding that breastfeeding lowers the risk of TNBC in younger women is important, particularly for
those who have several children. Almost 40% of breast cancers diagnosed in younger African American women are TNBC. The benefits of breastfeeding regarding breast cancer, and TNBC in particular, is an important public health message for young women starting a family.”   

Breast Cancer Family Registry, and the Los Angeles County Asian American Breast Cancer Study, which collectively included a total of 5,669 women, 558 with TNBC and 5,111 controls who never had breast cancer. This is one of the largest studies of TNBC. Only a few studies have examined the link between childbirth and breastfeeding and the risk of developing TNBC. 
To conduct this study researchers combined data from three population-based breast cancer studies; the San Francisco Bay Area Breast Cancer Study, the Northern California site of the The Breast Cancer Etiology in Minorities Study was funded by grant R03 CA199343 from the National Cancer Institute. The San Francisco Bay Area Breast Cancer Study was supported by grants R01 CA63446 and R01 CA77305 from the National Cancer Institute, grant DAMD17-96-1-6071 from the U.S. Department of Defense and grant 7PB-0068 from the California Breast Cancer Research Program. The Northern California site of the Breast Cancer Family Registry was funded by grant UM1 CA164920 from the National Cancer Institute. 

About the Cancer Prevention Institute of California
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