Low pectoralis major muscle mass predicts the risk of post-surgical bleeding after mastectomy in patients with breast cancer.

PURPOSE: Post-surgical bleeding is a clinically relevant complication after mastectomy. Although high body mass index (BMI) is associated with the risk of this complication, the impact of regional skeletal muscle mass adjacent to the operative field remains unclear. This study aims to evaluate the association between pectoralis major muscle mass and post-surgical bleeding after mastectomy in patients with breast cancer. METHODS: We retrospectively analyzed 669 patients who underwent mastectomy between 2015 and 2022, involving a total of 709 breasts. The pectoralis major muscle area was measured using preoperative computed tomography (CT) at the Th2 level, and the pectoralis major muscle index (PMI) was then calculated as the muscle area divided by height squared. We analyzed the association between BMI and PMI, and the incidence of post-surgical bleeding. RESULTS: Post-surgical bleeding occurred in 42 cases (5.9%). Patients who experienced bleeding had significantly higher BMI (26.1 ± 4.7 vs. 22.8 ± 3.8, p < 0.0001) and lower PMI (2.76 ± 0.69 vs. 3.12 ± 0.82, p < 0.001) than those without bleeding. BMI and PMI were weakly correlated (r = 0.16). On multivariate analysis, high BMI (hazard ratio [HR] 1.38, 95% confidence interval [CI] 1.27-1.52, p < 0.0001) and low PMI (HR 0.18, 95% CI 0.09-0.32, p < 0.0001) were independently associated with an increased risk of post-surgical bleeding. Combined stratification demonstrated that patients with a high BMI and low PMI had the highest incidence of bleeding (20.1%), whereas those with a low BMI and high PMI had the lowest risk (1.3%). CONCLUSIONS: Low PMI and high BMI are independent predictors of post-surgical bleeding after mastectomy. Assessment of regional muscle mass using preoperative CT may enhance perioperative risk stratification in patients with breast cancer.