FRIDAY, July 20 (HealthDay News) -- Body mass index (BMI) affects the level of estradiol and estrone sulfate suppression achieved when treating postmenopausal women with estrogen receptor (ER)-positive breast cancer with either of two aromatase inhibitors, anastrozole or letrozole, according to a study published online July 16 in the Journal of Clinical Oncology.

To examine the correlation between estrogen suppression and aromatase inhibitors and BMI, Elizabeth Folkerd, Ph.D., of the Royal Marsden National Health Service Foundation Trust in London, and colleagues evaluated plasma estradiol and estrone sulfate levels with a highly-sensitive radioimmunoassay for 44 postmenopausal women with ER-positive breast cancer. Participants were treated with anastrozole then letrozole for three months each or vice versa.

The researchers observed a significant correlation between baseline values of estradiol and estrone sulfate and BMI. At higher BMI, the levels of estrogen were greater for patients receiving treatment with both aromatase inhibitors, and this effect was significant with letrozole. Across all ranges of BMIs in the study, suppression of both estrogen types was greater with letrozole.

"Limited data suggest that these findings could be clinically relevant, but far more work is needed to determine whether modest differences in degree of estrogen suppression have an impact on the efficacy of the aromatase inhibitors," write the authors of an accompanying editorial. "Until further information is available, these findings should not lead to changes in the choice of hormonal agents for women with early breast cancer."

One author disclosed financial ties to the pharmaceutical industry.

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