Does Obesity Increase Breast Cancer Mortality?

obese white woman What You Kneed to Know: A new large study suggests that the presence of obesity increases the risk of death due to breast cancer among premenopausal women with estrogen receptor-positive (ER+) breast cancer. Obesity had little effect in postmenopausal women, and no effect in estrogen receptor-negative (ER-) disease. The Evidence: Investigators from the Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) compared records of 80,000 women enrolled in 70 clinical trials. The authors defined obesity as a body mass index (BMI) of 30 or higher, and normal as 20 to 25. The investigators collected data on estrogen receptor status, menopausal status, cancer recurrence, and death.

  • Among premenopausal women with estrogen receptor positive breast cancer, obesity increased the risk of a breast cancer-related death by a factor of 1.34.
  • At 10 years, breast cancer-related mortality was reported in 21.5% of obese women and 16.6% of normal weight women, a difference of about 5%.

My Take: These results are surprising, as obesity substantially increases blood estrogen levels in postmenopausal women only, so one would expect to increase risk among only pre- and post-menopausal women with estrogen-driven tumors (ER+). We know that obesity and being overweight are linked to an increased risk of developing ER+, postmenopausal breast cancer.

  • Obesity is often associated with low-grade chronic inflammation of fat (adipose) tissue in the breast and can activate an enzyme (aromatase) that causes tissue production of estrogen. So I am surprised that the effects of obesity are less clear among postmenopausal women, as compared to premenopausal women.
  • If we continue along the track we are going, obesity may replace tobacco consumption as the leading modifiable risk factor for cancer. In the USA, about two-thirds of us are overweight or obese.
  • If you are able, keep moving. Even 150 minutes per week of the equivalent of a brisk walk may decrease your risk of heart attack, stroke, dementia, and cancer.

I’m Dr. Michael Hunter. Reference: Pan H, Gray RG, on behalf of the Early Breast Cancer Trialists’ Collaborative Group: Effect of obesity in premenopausal ER+ early breast cancer: EBCTCG data on 80,000 patients in 70 trials. ASCO Annual Meeting. Abstract 503. Presented May 31, 2014. 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. Available now: Understand Colon Cancer in 60 Minutes; Understand Brain Glioma in 60 Minutes. Both can be found at the Apple Ibooks store. Coming Soon for iPad: Understand Breast Cancer in 60 Minutes; Understand Colon Cancer in 60 Minute; Understand Colon Cancer in 60 Minutes; Understand Brain Glioma in 60 Minutes. Thank you.

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Harvard AB Yale MD UPenn Radiation Oncology Radiation Oncologist, Seattle area

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