Increasing BMI is associated with both endometrioid and serous histotypes among endometrial rather than ovarian cancers: a case-to-case study

Aim: Although obesity has been associated with endometrioid (type I) and, to a lesser extent, with serous (type II) endometrial cancer (EC), the association with the same histotypes of ovarian cancer (OC) remains unclear. Therefore, we intended to compare the role of BMI in carcinogenesis of endometrioid and the serous malignancies, at both ovarian and endometrial level. Methods: A retrospective case-to-case study was performed in the University Hospital of Bologna (Italy), through the review of primary EC matched with the corresponding OC cases in the same period (1988–2017). Results: We included 1052 women diagnosed with EC (n = 897 endometrioid, n = 52 serous) and 955 women affected by OC (n = 132 endometrioid, n = 627 serous). EC patients had higher median BMI than women diagnosed with OC (27.3 [23.4–31.9] vs 24.9 [21.7–27.5], p < 0.01). After controlling for confounding, 1 unit increase in BMI was associated with a 5% higher odds of endometrial as opposed to ovarian cancer (OR for ovarian as opposed to endometrial cancer 0.95; 95% CI 0.91–0.98, p = 0.004). Conclusions: Increasing BMI is associated with endometrial rather than ovarian cancer, among both serous and endometrioid histotypes.