Following treatment with hormone-suppressing drugs, women who are obese continue to have higher levels of estrogen than women of normal weight. Thus, a team from The Institute of Cancer Research in London and The Royal Marsden NHS Foundation Trust examined the possibility that women who are obese might benefit from changes to their treatment.
The study, published in the Journal of Clinical Oncology, found that hormone-suppressing drugs noticeably reduced estrogen levels in obese women, yet levels of estrogen remained more than double those in women of normal weight.
Senior author Professor Mitch Dowsett, a team leader in the Breakthrough Breast Cancer Research Centre at The Institute of Cancer Research, said: “We found that women with higher BMIs [body mass indexes] 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.”
Scientists stressed the effect of obesity on treatment was modest, and “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,” Dowsett said.
The team examined a recent study that indicated that the aromatase inhibitor anastrozole was no more effective than older-style tamoxifen in women with higher BMIs, unlike in the general population where it is clearly more effective. Professor Dowsett and colleagues also wanted to investigate whether aromatase inhibitors are less effective in general in women with higher BMIs.
The aromatase inhibitors anastrozole and letrozole were studied. The researchers evaluated 54 postmenopausal women with estrogen receptor–positive breast cancer who were treated at the Edinburgh Breast Unit. Their treatments included either 3 months of adjuvant anastrozole followed by 3 months of letrozole, or vice versa. Data on estrogen levels and BMIs measured before and after treatment with the first drug were available for 44 patients.
Study results showed that prior to treatment, women with higher BMIs had higher estrogen levels. More specifically, those with BMIs from 30 to 35 had around 3 times more plasma estrogen than those with BMIs of less than 25.
After treatment with letrozole, women with BMIs of 30 to 35 still presented with estrogen levels nearly 3 times as high as those for healthy-weight women. The same trend applied to those treated with anastrozole; however, it did not reach statistical significance.
Professor Alan Ashworth, Chief Executive of The Institute of Cancer Research, said: “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.”