The impact of BMI and obesity on breast cancer: A prospective cohort study

Abstract

Objective: To evaluate the association between BMI and breast cancer stage at presentation in Basrah, Iraq.

Methods: This prospective cohort study enrolled consecutive women diagnosed with breast cancer at two Basrah teaching hospitals from December 2020 to December 2022. BMI was measured at presentation and categorised per WHO thresholds. Cancer stage was determined through clinical examination, imaging, and histopathology by multidisciplinary teams. Univariate analyses employed Kruskal-Wallis and Fisher's exact tests. Multivariable binary logistic regression assessed independent predictors of advanced stage (III/IV). Statistical significance was set at p<0.05.

Results: Among 121 women (mean age 50.8±11.0 years), obesity (BMI≥30) occurred in 56 (46.3%). Most presented with a breast lump (90, 74.4%) and tumour size 2-5 cm (75, 62.0%). Stage distribution: I (26, 21.5%), II (58, 47.9%), III (29, 24.0%), IV (8, 6.6%). Of stage IV patients, five (62.5%) were obese. No significant association existed between BMI and stage in univariable analysis (p=0.392). Tumour size is strongly associated with stage (p<0.0001). After multivariable adjustment, BMI remained non-significant (obesity adjusted OR: 1.42, 95% CI 0.51-3.96, p=0.502).

Conclusions: Despite high obesity prevalence, BMI alone did not independently predict advanced stage. Tumour size was the strongest correlate. These findings highlight adiposity-breast cancer complexity, supporting alternative anthropometric measures in future research.