Obesity and Early-Stage Breast Cancer: A Comprehensive Analysis of Tumor Biology, Staging Accuracy, and Long-Term Outcomes.

Background: Obesity increases the risk of breast cancer by approximately 10% for every 5-unit increase in body mass index (BMI), underscoring its role as a key modifiable risk factor. Objective: To determine the prevalence of obesity among early-stage breast cancer patients at an academic breast unit and to evaluate its association with tumor characteristics, surgical outcomes, and survival, with a particular focus on premenopausal women. Methods: Prospectively collected data from patients treated between January 2005 and December 2023 were retrospectively analyzed. Statistical analyses, including chi-squared tests, ANOVA, Kaplan-Meier, and univariate regression analyses, were used to assess obesity prevalence, tumor size, axillary staging accuracy, molecular subtypes, surgical margins, recurrence, survival, and menopausal status. Results: Among 1187 patients, 55.6% were normal weight, 25.4% were overweight, and 19% were living with obesity (BMI > 30). Obesity was more common in patients > 50 years of age (22% vs. 10%; p = 0.001). Mean tumor size increased with BMI (13.8 vs. 15.4 mm vs. 17.6 mm; p = 0.001). Notably, in premenopausal patients, obesity correlated with a higher proportion of poorly differentiated (G3) tumors (50% vs. 27%; p < 0.05), while survival remained similar across BMI categories. Conclusion: Obesity is associated with larger tumors, poorer axillary staging, and a higher prevalence of aggressive histological subtypes among premenopausal patients. However, obesity did not significantly influence overall survival. Targeted screening and multidisciplinary management strategies are essential to improve early detection and individualize treatment for patients with obesity.