Obesity and early postoperative prognosis in triple-negative breast cancer: a real-world cohort study with time-varying hazard analysis

Obesity is a known risk factor for breast cancer; however, data on its impact on survival outcomes in patients with triple-negative breast cancer (TNBC)—particularly regarding the dynamic changes in risk over time—remain insufficient. Patients with TNBC who underwent surgical treatment between 2012 and 2020 were selected. After propensity score matching, 99 obese patients (BMI ≥ 28 kg/m²) and 405 non-obese patients (BMI < 28 kg/m²) were included in the study. Follow-up continued through December 2025. The study assessed patient demographic characteristics, tumor characteristics, and survival outcomes (disease-free survival, overall survival, and distant disease-free survival). Survival analysis utilized Kaplan-Meier curves and Cox models, incorporating time-varying hazard ratios and landmark analysis. The impact of obesity on TNBC survival was primarily observed during the first 2 years post-surgery, manifesting as poorer 2-year disease-free survival ( P = 0.043) and 2-year distant disease-free survival ( P = 0.021). However, no significant differences were observed in long-term disease-free survival, overall survival, or long-term distant metastasis-free survival. Time-varying hazard ratio curves showed that the risks of recurrence and death associated with obesity peaked early (within approximately 20 months post-surgery) and then gradually declined. Subgroup analyses indicated that obesity was significantly associated with reduced 2-year disease-free survival in the following subgroups: patients with negative lymph nodes ( P = 0.017), TNM stage I ( P = 0.020), and those who underwent total mastectomy ( P = 0.036). Furthermore, obesity was associated with an increased long-term local recurrence rate ( P = 0.026) and a higher risk of liver metastasis at 2 years ( P = 0.015) in patients with TNBC. Obesity is associated with a higher risk of recurrence and metastasis within two years after surgery for TNBC, particularly among patients with early-stage TNBC or those who have undergone mastectomy.