Obesity may affect response to breast cancer treatment

Women who are obese continue to have higher levels of oestrogen than women of normal weight even after treatment with hormone-suppressing drugs, raising the possibility that they might benefit from changes to their treatment.

The study, led by Professor Mitch Dowsett, a team leader in the Breakthrough Breast Cancer Research Centre at the ICR and head of the academic department of biochemistry at The Royal Marsden, found hormone-suppressing drugs called aromatase inhibitors did markedly reduce oestrogen levels in obese women – but that their levels of oestrogen remained more than double those of women of normal weight.

Professor Dowsett and colleagues set out to probe a recent study that indicated the aromatase inhibitor anastrozole was no more effective than older-style tamoxifen in women with higher BMI, unlike in the general population where it is clearly more effective.

The study included 54 postmenopausal women with oestrogen receptor positive breast cancer who were treated with either three months of adjuvant anastrozole followed by three months of the more potent aromatase inhibitor letrozole, or these drugs in the opposite sequence.
The team found that, prior to treatment, women with higher BMIs had higher oestrogen levels – those with BMIs from 30 to 35 had around three times more plasma oestrogen than those with BMIs of less than 25.
After treatment with letrozole, women with BMIs of 30 to 35 still had levels of plasma oestrogen nearly three times as high as for healthy-weight women. The same trend was found for anastrozole, but did not reach statistical significance.

Professor Dowsett said: “Our study takes us a step closer to understanding which of the treatment options available might be the most suitable for individual women.”

The study published in the Journal of Clinical Oncology.