Is there a different effect of excess body weight on cancer risk in type 1 and type 2 endometrial cancer?

Abstract

Background: Endometrial cancer (EC) is the fifth most common type of cancer in women worldwide being responsible for 4.8% of all cancers in women. From large cohort studies there is consistent evidence for a positive association between excess body weight and different cancer types. Women with excess body weight stands out as having a particularly high relative risk for EC. Excess body weight is an increasing health problem worldwide and a deeper understanding of the association between excess body weight and EC subtypes is needed. Objective: The main aim of this master’s thesis is to assess if the effect of excess body weight on cancer risk is different in type 1 and type 2 EC. Material and methods: Data from the Norwegian Women and Cancer (NOWAC) study, a national population-based cohort study in Norway, was used. Participants were followed from 1991 until 2016. Cox proportional hazard regression was used to explore the effect of body mass index (BMI) on the risk of type 1 and type 2 EC. To evaluate whether the association between excess body weight and EC varied between type 1 and type 2 EC, the effect estimates were compared using a heterogeneity test, which follows an approximate chi square distribution. Results: For every increase of two body mass index (BMI) units, the risk of type 1 EC increased significantly by 21% (HR=1.21, 95% CI: 1.71, 1.25). For type 2 EC, the corresponding number was 11% (HR=1.11, 95% CI: 1.03, 1.20). Women who were overweight (BMI  25.0 kg/m2) had 35% increased risk of type 1 EC (HR=1.35, 95% CI: 1.07, 1.69) and women with obesity had a 3-fold higher risk of type 1 EC (HR=3.00, 95% CI: 2.25, 3.88) compared to women with normal weight. Women who were overweight had no increased risk of type 2 EC (HR=1.05, 95% CI: 0.70, 1.58), whereas women with obesity had a 95% higher risk of type 2 EC (HR=1.95, 95% CI: 1.15, 3.31), compared to women with normal weight. The associations between BMI and EC risk did not differ significantly between the two subtypes. Conclusion: In summary, BMI was associated with type 1 and type 2 EC in a dose response manner. The association between excess body weight and type 1 and type 2 EC does not significantly differ according to subtypes, however, the association seems to be stronger in type 1. This could support the idea that estrogen plays a more important role in the development of type 1 ECs compared to type 2 EC.