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.