Prognostic value of psoas major muscle density in patients with breast cancer metastases to bone: a retrospective single-center cohort study.

Objective Although sarcopenia is associated with poor prognosis for cancer patients, the relationship between muscle quantity and quality, and prognosis of breast cancer patients with bone metastases is unclear. This study aims to evaluate the association of muscle parameters, muscle area and density, and overall survival (OS) from the diagnosis of bone metastases in breast cancer patients with bone metastases. Methods This study retrospectively investigated the prognostic value of muscle area and density in 90 women who were diagnosed with breast cancer with bone metastases between September 2005 and June 2018. We measured psoas major muscle and paravertebral muscle area and density on single axial computed tomography images at the L3 level and subgrouped the patients into higher or lower groups for each muscle measurement, using median values as cutoffs. We evaluated associations between OS and muscle parameters, using a Cox proportional hazards model adjusted by age and prognostic score for bone metastases (modified Katagiri score). Results Median OS among patients with lower psoas major muscle density (25 months) was significantly shorter than in the higher psoas major muscle density group (61 months; hazard ratio: 1.79, 95% confidence interval: 1.01-3.16, P = 0.045). However, muscle area and paravertebral muscle density were not associated with OS in this setting. Conclusion Lower psoas major muscle density was a predictor of poor prognosis in patients with breast cancer metastases to bone. The association between psoas major muscle density and prognosis allows wider research into interventions that can prevent loss of muscle density.