Obesity Is an Independent Prognostic Factor That Reduced Pathological Complete Response in Operable Breast Cancer Patients

<i>Background and Objectives</i>: Obesity is a significant risk factor for the development of breast cancer (BC) and associated poorer outcomes. A pathological complete response (pCR) with neoadjuvant chemotherapy (NACT) correlates with improved long-term prognosis in BC patients. In this study, we aimed to investigate the predictive effect of obesity on achieving pCR following NACT. <i>Methods</i>: This single-center retrospective study included patients with operable BC who were treated with NACT. Patients were categorized based on their pre-chemotherapy body mass index (BMI), including non-obese (<30 kg/m²) and obese (≥30 kg/m²) groups, and pathological responses to NACT were compared. <i>Results</i>: A total of 191 female patients were included in this study; of these, 83 (43.4%) were obese and 108 (56.6%) were in the non-obese group. Obesity was more common in postmenopausal patients, and the median age of obese patients was significantly higher compared to non-obese patients. Patients in the obese group demonstrated significantly lower pCR rates compared to the non-obese group (30% vs. 45%, <i>p</i> = 0.03). The histological subtype assessment indicated that only in the HR-positive/HER2-negative patients was the pCR rate significantly lower in the obese group compared to the non-obese group (11% vs. 27%, <i>p</i> = 0.05). According to menopausal assessment, a significant difference in pCR rates was observed only among postmenopausal patients, with rates of 29% in the obese group compared to 52% in the non-obese group (<i>p</i> = 0.03). In logistic regression analysis, obesity (OR: 0.52, 95% CI: 0.28-0.97; <i>p</i> = 0.04) and a low Ki-67 score (HR: 2.7, 95% CI: 1.37-5.53; <i>p</i> = 0.003) were independently associated with a decreased rate of pCR. <i>Conclusions</i>: The impact of obesity on achieving pCR in BC patients undergoing NACT remains controversial. Our study revealed that obesity was an independently significant negative predictive factor for achieving pCR.