WOMEN WITH EARLY-STAGE hormone receptor-positive breast cancer often receive endocrine therapy for at least five years to prevent cancer recurrences after surgery and other treatments. But extended treatment comes with potential drawbacks.

People taking the most common endocrine therapies—aromatase inhibitors and tamoxifen—may experience side effects, including joint pain, hot flashes and fatigue, during treatment. Researchers have also noted possible links between aromatase inhibitors and elevated risk for cardiometabolic conditions, which was the subject of a study presented April 19 at the American Association for Cancer Research (AACR) Annual Meeting 2026 in San Diego. (The AACR publishes Cancer Today.)

“Both therapies have been shown to be incredibly efficacious. They substantially improve survival while at the same time they substantially [reduce the] opportunity for cancer recurrences. But they definitely have their fair share of side effects,” said Jorge Ledesma, the study’s presenter and a researcher who studies the methods by which patients receive cancer treatment at Kaiser Permanente Northern California Division of Research in Pleasanton, California.

For this study, Ledesma and colleagues analyzed data for more than 8,000 women to see whether consistently taking an endocrine therapy for five years raised a woman’s risk for developing high blood pressure, high cholesterol or diabetes. They used data from a cohort of postmenopausal women in the Kaiser Permanente Northern California health system who were diagnosed with stage I to III hormone receptor-positive breast cancer from November 2005 to March 2023.

Researchers categorized women based on the type of endocrine therapy they received and whether they adhered to the prescribed schedule for taking endocrine therapy. Researchers considered patients to be adherent to treatment if they received enough medicine to cover at least 80% of their prescribed dose for the year.

The study found that the proportion of women with elevated blood pressure was 6.4 percentage points higher in women who took aromatase inhibitors for the full five years than it was for women who did not meet the 80% threshold for any year during treatment. Adherent patients had a 29.1% chance of developing high blood pressure, and nonadherent patients had a 22.7% chance.

Similarly, rates of high cholesterol were 6.8 percentage points higher in women who consistently took an aromatase inhibitor. They had a 32.4% chance, compared with 25.6% in nonadherent patients. And rates of diabetes were 12.6% in women who stayed on aromatase inhibitors, compared with 8.9% in nonadherent patients, a difference of 3.7 percentage points.

People taking tamoxifen were more likely to have high blood pressure than people who were not adherent, but they did not have increased rates of cholesterol or diabetes. Ledesma said previous research suggests tamoxifen may be beneficial in some measures of heart health.

The study analyzed differences based on how patients received treatment in clinics, so other differences between women who adhered to treatment and those who did not could affect these health outcomes. The study found women who were treatment adherent for at least five years were younger, lived in higher-income neighborhoods, were more likely to have received chemotherapy and were less likely to smoke cigarettes than those who were nonadherent.

Despite the increased cardiometabolic risk, the 10-year overall survival was 36% lower among people who did not stick to the treatment schedule, Ledesma said.

“These findings really emphasize the importance of being able to maintain adherence to endocrine therapy while also being able to monitor closely cardiometabolic health,” Ledesma said.

Eric Fitzsimmons is an editor at Cancer Today.