Aromatase Inhibitors May Limit Effectiveness of Weight Loss Medications in Breast Cancer Survivors

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Aromatase inhibitors may interfere with the efficacy of weight loss medications in breast cancer survivors, according to a new study presented by Fansa et al at the 2023 Endocrine Society Annual Meeting.


Aromatase inhibitors are designed to block the activity of the aromatase enzyme, which the body uses to make estrogen in the ovaries and other tissues. The agents are used to treat or prevent recurrence in patients with breast cancer. They may also be used to help prevent breast cancer from occurring in those who may be at high risk of developing the disease. Blocking aromatase has been shown to lower the amount of estrogen made by the body and potentially stop the growth of cancer cells that require estrogen.

However, previous studies have shown that aromatase inhibitors may also be a risk factor for weight gain. Weight gain and obesity—in addition to being associated with breast cancer recurrence and cancer-related mortality—can lead to cardiovascular disease and cardiovascular-related mortality.

“Weight gain is a common concern in breast cancer survivors,” explained lead study author Sima Fansa, MD, a medical student at the American University of Beirut. “This is the first study assessing response to weight loss medications in a subgroup of breast cancer survivors taking aromatase inhibitors,” she added.

Study Methods and Results

In the new study, investigators compared the outcomes of 63 breast cancer survivors who were undergoing treatment with aromatase inhibitors and taking weight loss medications—including liraglutide, semaglutide, and phentermine—with those of 36 individuals without a history of breast cancer who were not receiving aromatase inhibitors but were taking the weight loss medications.

The investigators found that the weight loss medications were possibly less effective in the breast cancer survivors than those without a history of breast cancer.

The breast cancer survivors lost less weight at 3, 6, and 12 months of follow-up (3.7%, 3.9%, and 5.2%, respectively); whereas those without a history of breast cancer demonstrated a higher capacity for weight loss (5.6%, 9.5%, and 10.5%, respectively).

“We believe that this difference may be explained, at least partially, by the anti-estrogen effect of aromatase inhibitors,” Dr. Fansa noted. “Aromatase inhibitors can lead to decreased muscle mass, increased fat mass, and changes in energy expenditure. This may affect the body’s response to weight loss interventions—including weight loss medications,” she stressed.


“Our results highlight the need to develop better approaches to manage weight gain in patients with a history of breast cancer taking aromatase inhibitors,” Dr. Fansa emphasized. “Preventing weight gain in this group or treating obesity [may] effectively … improve breast cancer outcomes, prevent further health complications, and improve quality of life for these [patients],” she concluded.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.