Association of metabolic syndrome conditions with risk of second primary uterine cancer in breast cancer survivors

Purpose Uterine cancer risk is high in breast cancer survivors. Although breast cancer and uterine cancer share some common epidemiological risk factors, association of metabolic syndrome with incident uterine cancer in breast cancer survivors is under-studied. We evaluated the association of metabolic syndrome conditions with second primary uterine cancer in breast cancer survivors. Methods In this retrospective cohort study, 37,303 breast cancer patients diagnosed between 2008 and 2020 at Kaiser Permanente Southern California, an integrated healthcare system, were included. Data on cancer-related variables, sociodemographic, and clinical variables were extracted from KPSC’s Surveillance, Epidemiology, and End Results (SEER)-affiliated cancer registry and electronic health records, as appropriate. Patients were followed from breast cancer diagnosis until 12/31/2021 for incident uterine cancer. Proportional hazards regression was used to report association [HR (95% CI)] between metabolic conditions and uterine cancer. Results More than half (53.1%) of the breast cancer survivors had 1–2 metabolic conditions; 19.4% had 3 + , while 27. 5% had no metabolic conditions. Median time to follow-up was 5.33 years and 185 (0.5%) patients developed second primary uterine cancer. Obesity was associated with an elevated uterine cancer risk in the adjusted model [HR (95% CI) 1.64 (1.20–2.25)]. Having 1–2 metabolic conditions (versus none) was not associated with increased uterine cancer risk [adjusted HR (95% CI) 1.24 (0.85–1.82)]; however, there was an increased uterine cancer risk with 3 + metabolic conditions [adjusted HR (95% CI) 1.82 (1.16–2.87)]. Conclusion Although not statistically significant, we found a trend demonstrating greater uterine cancer risk by increasing numbers of metabolic syndrome conditions in breast cancer survivors.