Association of Pectoralis Muscle Area and Survival Outcomes after Chemotherapy.

e24094 Background: Chemotherapy use may be associated with muscle wasting, a marker of frailty that can predispose individuals to poor outcomes. We assessed the association between pre-treatment pectoralis muscle area and overall mortality following chemotherapy. Methods: We identified individuals diagnosed with breast cancer (N=221), lymphoma (N=216), or sarcoma (N=115) who received chemotherapy at the University of Minnesota Masonic Cancer Clinic and had CT scans prior to chemotherapy 2009-2014. Using CoreSlicer, right pectoral muscle area was measured at baseline and indexed to body surface (right pectoralis muscle area [cm2] / body surface [m2]) and divided into quartiles. Restricting to individuals who started chemotherapy within 6 months after their CT, we used cox regression (adjusted for age, sex, cancer type, stage, ever-smoking, BMI, and chemotherapy type) to assess associations between baseline muscle area and overall survival, testing for nonlinear effects using cubic splines. Results: 536 individuals (66% female) were identified who were treated with anthracyclines based chemotherapy (N=408), Trastuzumab (N=64), or both (N=64). Mean baseline muscle area was 14.9 (4.6) cm2 in females and 26.3 (9.3) cm2 in males. Median follow-up was 4.6 years. Larger baseline pectoralis muscle area (per m2 body surface) was associated with improved survival (adjusted model, overall effect, P=0.01), with some nonlinear effects (P=0.05). With muscle area (per m2 body surface) categorized as quartiles, individuals in the 3rd and 4th quartiles were at lower risk of dying (compared with people in the 1st quartile, hazard ratios 0.59 and 0.55 respectively, 95% CI range 0.35-0.90, P=0.01). There were no differences comparing the 4th vs the 3rd quartile (P=0.79), or the 2nd vs the 1st quartile (P=0.5). Conclusions: We found a protective association between larger right pectoral muscle size (relative to body surface) and overall survival after chemotherapy. There may be ceiling and threshold effects given evidence for nonlinear effects, since neither the 2nd vs. 1st quartile, nor the 4th vs. 3rd quartile comparisons in the categorical model were significant. Hazard ratios and confidence intervals of overall mortality by pectoral muscle area at baseline indexed to body surface, N=536, 2009-14. [Table: see text]