Lactation Tied to Aggressive Breast Cancer in Mexican Women

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The available evidence indicates that a woman can reduce her risk of breast cancer by breastfeeding, having multiple children before age 29-30, and giving birth at a younger age. But is this true for all subgroups of women? A recent study led by investigators from the University of California, San Diego suggest that women of Mexican descent with more children and those who breastfed are more likely to be diagnosed with an aggressive form of breast cancer.

The Study: The Ella Binational Breast Cancer Study assessed the association between reproductive factors and breast tumor subtypes among 1041 Mexican and Mexican-American female cancer patients. The Ella study enrolled breast cancer patients at the University of Arizona Cancer Center, the University of Texas, MD Anderson Cancer Center, and 3 sites in Mexico – the Universidad de Sonora, the Instituto Tecnologico de Sonora, and the Universidad de Guadalajara.

Results: The researchers found that breastfeeding in women of Mexican descent is linked to triple negative breast cancer, an more aggressive type not driven by estrogen, progesterone, or HER-2. This was true for those who breastfed for 12 months of more (the risk for getting triple negative breast cancer doubled among this group!). Let’s look by particular risk factors, comparing the chances of having an aggressive type (triple negative) versus a more well-behaved type (luminal A, or expressing estrogen and progesterone receptors, but not the bad HER2 receptor):

Late age at first pregnancy: Less likely to get triple negative breast cancer (TNBC); odds ratio 0.61.

Three or more full-term pregnancies: More likely to have TNBC (odds ratio 1.68).

Breast-feeding more than 12 months: Twice as likely to have TNBC (compared to the better behaving luminal A type)

My Take: These result are a bit troubling. In general, breastfeeding is linked to better outcomes among mothers and children. Clearly we need confirmatory evidence of the association between lactation and the risk of triple negative breast cancer (TNBC). To me the takeaway message is that we need to do additional research into populations with unique risk-factor patterns. Individuals in such groups might benefit from prevention and screening strategies that are tailored specifically to them. In addition, I recall that while more pregnancies can decrease the overall risk of getting breast cancer, it can increase the risk of TNBC among the general population, so these findings may not be novel.  The positive? Going forward, we should be better able to individualize risk-reducing and screening strategies. I’m Dr. Michael Hunter.

The small print: The material presented herein is informational only, and is not designed to provide specific guidance for an individual. Please check with a valued health care provider with any questions or concerns. As for me, I am a Harvard- , Yale- and UPenn-educated radiation oncologist, and I practice in the Seattle, WA (USA) area. I feel genuinely privileged to be able to share with you. If you enjoyed today’s offering, please consider clicking the follow button at the bottom of this page.

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Reference: Martinez ME, Wertheim BC, Natarajan L, et al. Cancer Epidemiology Biomarkers & Prevention. 2013; DOI:10.1158/1055-9965.EPI-13-0560.

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