History of Breast Cancer, Aromatase Inhibitor Use Could Blunt Benefit from Weight Loss Medications

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A matched case-control study of nearly 100 women details the reduced effect of anti-obesity medications in those with a history of breast cancer and aromatase inhibitor use.

New research suggests survivors of breast cancers who received aromatase inhibitors may receive less benefit from weight loss medications than their counterparts without breast cancer and not taking aromatase inhibitors.

Presented at the Endocrine Society 2023 annual meeting, results of the matched case-control retrospective study found women with a history of breast cancer taking aromatase inhibitors had a lower total body weight loss with liraglutide, semaglutide, and phentermine at 3, 6, and 12 months relative to their counterparts without breast cancer and not taking aromatase inhibitors.1

“This is the first study assessing response to weight loss medications in a subgroup of breast cancer survivors taking aromatase inhibitors,” said lead investigator Sima Fansa, MD, of the Mayo Clinic in Minnesota.2 “Our results highlight the need to develop better approaches to manage weight gain in patients with a history of breast cancer taking aromatase inhibitors. Preventing weight gain in this group or treating obesity effectively will improve breast cancer outcomes, prevent further health complications, and improve quality of life for these people.”

The obesity epidemic has ballooned in the US and across the globe in recent decades. As the options for anti-obesity medications have expanded in recent years, a new emphasis on personalizing weight loss management has emerged. With this in mind, Fansa and a team of investigators from Mayo Clinic sites in Minnesota and Florida launched the current study to assess the effects of weight loss outcomes with these medications in patients taking aromatase inhibitors for breast cancer treatment. To do so, investigators designed their study as a matched case-control retrospective cohort study of breast cancer survivors on aromatase inhibitors using anti-obesity medications compared to a group of female patients with obesity using anti-obesity medications and without a history of breast cancer or aromatase inhibitor use.1

For the purpose of analysis, patients were matched by age and BMI. Investigao5rts pointed out exclusion criteria included anti-obesity medication initiation prior to aromatase inhibitor therapy, less than 3 months of anti-obesity medication use, history of bariatric surgery, active malignancy, or pregnancy. The primary outcome of interest for the study was total bod weight loss percentage at 12 months. Secondary outcomes of interest included total body weight loss percent at 3 and 6 months as well as the percent of patients achieving 5% or more, 10% or more, 15% or more total body weight loss at 12 months.1

Overall, 99 patients were included in the study. Of these, 63 were included in the aromatase inhibitor cohort and 36 were included in the control group. The aromatase inhibitor cohort had a mean age of 63.5 (Standard deviation [SD], 10) years and a mean BMI of 34.4 (SD, 7.0) kg/m2. The control cohort had a mean age of 60.4 (SD, 8.7) years and mean BMI of 36.3 (SD, 6.9) kg/m2. Investigators pointed out the 3 anti-obesity medications used among study participants were liraglutide, semaglutide, and phentermine, with no difference in frequency of use between either cohort (P = .1).1

Upon analysis, results indicated the aromatase inhibitor cohort had a lower total body weight loss percentage at 3 months (3.7% [SD, 4.3] vs 5.6% [SD, 4.1]; P = .03), 6 months (3.9% [SD, 4.3] vs 9.5% [SD, 4.7]; P <.0001), and 12 months (5.2% [SD, 5.3] vs 10.5% [SD, 6.8]; P < .0001). Investigators noted those in the aromatase inhibitor group were more likely to use lower doses of anti-obesity medications (P = .0004), but further analysis revealed total body weight loss percent differences persisted among groups after adjustment for dosing (P < .0001).1

Investigators highlighted the percentage of patients achieving the aforementioned 5% or more (85.7% vs 50.0%; P < .0001), 10% or more (57.1% vs 20.0%; P < .0001), and 15% to more (28.6% vs 5.0%; P < .0001) thresholds of total body weight loss percent were greater in the control group relative to those in the aromatase inhibitor group. Additionally, investigators reported finding no predictors for total body weight loss at 12 months among the aromatase inhibitor group.1

“We believe that this difference may be explained, at least partially, by the anti-estrogen effect of aromatase inhibitors,” Fansa added.2 “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.”


  1. Fansa S, Ghusn W, Tama E, et al. Efficacy of Anti-obesity Medications Among Breast Cancer Survivors Taking Aromatase Inhibitors. Paper presented at: the Endocrine Society annual meeting. June 15 – 18, 2023.
  2. Endocrine Society. Some breast cancer treatments may limit effectiveness of weight loss medications. Endocrine Society. June 16, 2023. Accessed June 18, 2023.