Significance of skeletal muscle index-to-body mass index ratio as a predictor of post-surgical bleeding after mastectomy in patients with breast cancer

Background Post-surgical bleeding is a major complication of mastectomy in patients with breast cancer. However, the risk factors for post-surgical bleeding have not been well studied. Although obesity or reduced skeletal muscle mass is an indicator of cancer surgery complications, its impact on post-surgical bleeding after mastectomy remains unknown. Methods In total, 563 patients with breast cancer who underwent mastectomy were included in this study. We evaluated the preoperative body mass index (BMI), skeletal muscle index (SMI), and SMI-to-BMI ratio and analyzed the association between these values and the incidence of post-surgical bleeding. Results Post-surgical bleeding occurred in 33 (5.6%) patients. Mean BMI was significantly higher in the bleeding group (26.3 ± 4.7) than in the no-bleeding group (23.0 ± 4.1) ( p < 0.001), whereas mean SMI was lower in the former group (45.0 ± 8.5) than in the latter group (48.0 ± 8.5) ( p = 0.08). The bleeding group had significantly lower SMI-to-BMI ratio (1.71 ± 0.16) than the no-bleeding group (2.10 ± 0.23) ( p < 0.001). Among these three parameters, SMI-to-BMI ratio had the highest area under the curve value in their receiver operating characteristic curves (0.73 for BMI, 0.59 for SMI, 0.92 for SMI-to-BMI ratio). Furthermore, on multivariate analysis, SMI-to-BMI ratio was an independent risk factor for post-surgical bleeding (hazard ratio, 38.4; 95% confidence interval, 13.9–136.2; p < 0.001). Conclusions SMI-to-BMI ratio is a superior predictive factor of post-surgical bleeding after mastectomy to either BMI or SMI alone.