Fat Cells Cuddle Up With and Hold Estrogen

Breast cancer aromatase inhibitors and obesity

/ Author:  / Reviewed by: Robert Carlson, M.D

(RxWiki News) Obesity. Obesity. Obesity. It's spreading everywhere and touches most every chronic health condition. Now researchers find obesity could affect how well long-term breast cancer treatments work.

Fat holds onto estrogen, the hormone that feeds most (75 percent) breast cancers. So having too much fat means a woman is carrying around more estrogen than her normal weight peers.

A team of researchers at The Institute of Cancer Research in London and The Royal Marsden NHS Foundation Trust demonstrated that while hormone-blocking drugs known as aromatase inhibitors strongly reduce estrogen levels, the drugs don't work as well in obese women.

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Senior author Professor Mitch Dowsett, a team leader in the Breakthrough Breast Cancer Research Centre at The Institute of Cancer Research and head of the academic department of biochemistry at The Royal Marsden, said, "We found that women with higher BMIs had more estrogen remaining in their blood after treatment than healthy-weight women, which is consistent with previous suggestions that aromatase inhibitors might be slightly less effective in these women."

For the small study, Dr. Dowsett and his team evaluated two aromatase inhibitors - Arimidex (anastrozole) and Femara (letrozole) - in 54 postmenopausal women with estrogen receptor positive breast cancer.

They found that women with BMIs of 30-35 had three times the amount of estrogen in their blood as those with BMIs of 25 or less.

The women took each drug for three months. After three months of treatment with the letrozole, women with the higher BMIs still had three times the levels of estrogen as women of normal weights.

Anastrozole trends were the same, but did not reach statistical significance.

Adam Brufsky, MD, PhD, professor of medicine at the University of Pittsburgh School of Medicine, told dailyRx, "We have suspected this for a number of years, and it gives even more impetus to the concept that modest weight control (or at least body fat control) can improve outcomes for women with breast cancer."

Dr. Dowsett emphasized that these results should not change treatment plans or behaviors. "Women with higher BMIs should certainly not be alarmed by this finding or stop taking their treatment. Our study takes us a step closer to understanding which of the treatment options available might be the most suitable for individual women."

Professor Alan Ashworth, chief executive of The Institute of Cancer Research, concluded, "Aromatase inhibitors have played an increasing role in breast cancer treatment over the past decade, so it is important to understand the factors that affect how well they work in individual women in order to allow doctors to choose the best possible drug from the range available."

This study was published July 16 in the Journal of Clinical Oncology,

Financial information was not publicly available. 

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Review Date: 
July 17, 2012
Last Updated:
September 7, 2012