Association between body mass index and obesity-related cancer risk in men and women with type 2 diabetes in primary care in the Netherlands: a cohort study (ZODIAC-56)

OBJECTIVE: To investigate the relationship between body mass index (BMI) and obesity-related cancers in men and women with type 2 diabetes (T2D). DESIGN: Observational cohort study. SETTING: Primary care. PARTICIPANTS: A total of 52 044 patients with T2D who participated in the ZODIAC (Zwolle Outpatient Diabetes project Integrating Available Care) study between 1998 and 2012 was included (49% women). A dataset of these patients was linked to available information of the Netherlands Cancer Registry to obtain data on cancer incidents. PRIMARY OUTCOME MEASURES: Analyses were performed for the total group of obesity-related cancers and for non-sex-specific and sex-specific obesity-related cancers (in men: advanced prostate cancer, in women: ovarian, endometrial and postmenopausal breast cancer). RESULTS: The median follow-up period in all analyses was 3.1 (1.7–5.0) years in men and 3.1 (1.7–5.1) in women. During follow-up, 689 men and 914 women were diagnosed with an obesity-related cancer. In men, BMI was associated with a higher risk of the total group of obesity-related cancers and non-sex-specific obesity-related cancers (HR (per 5 kg/m(2) increase) 1.12 (95% CI 1.02 to 1.23) and HR 1.18 (95% CI 1.06 to 1.31)). No association was found with prostate cancer. In women, an association between BMI and all obesity-related cancers combined and sex-specific obesity-related cancers was present (HR 1.15 (95% CI 1.08 to 1.22) and HR 1.22 (95% CI 1.14 to 1.32)). No association with non-sex-specific cancers was found in women. CONCLUSIONS: BMI is associated with obesity-related cancers in men with T2D, except with advanced prostate cancer. The results of this study provide reason to reconsider the classification of advanced prostate cancer as an obesity-related cancer, at least in T2D. In women, BMI is associated with the total group of obesity-related cancers and with sex-specific obesity-related cancers.