Psoas muscle index as a novel measure of frailty and predictor of post-operative outcome in octogenarians with non-small cell lung cancer.

BACKGROUND: High body mass index (BMI) is a prevalent risk factor in a growing octogenarian population undergoing curative surgery for non-small cell lung cancer (NSCLC). Whilst BMI is paradoxically protective, its correlation with clinical frailty or objective fitness is unclear, due to the discrepancy of the ratio between muscle and adipose tissue. We aim to assess the relationship between sarcopenia and post operative survival and complications. METHODS: Demographic and clinical outcome data from octogenarians undergoing resections for primary NSCLC (January 2016-December 2021) was analysed retrospectively. Routine pre-operative positron emission tomography-computed tomography (PET-CT) scan was used to derive psoas muscle index (PMI) (bilateral measurement of cross-sectional psoas muscle area at the level of L3, divided by height-squared) as a measure of sarcopenia. RESULTS: A total of 189 patients were recruited with a mean age 82 years. Median overall survival (OS) was 2.7 vs. 3.0 years in males and females, respectively (P<0.001). Chronic obstructive pulmonary disease (COPD) (P=0.02) and pathological stage >Ia (P=0.02) reduced OS. In males, OS at 5 years increased with PMI (58.3% for ≥9.0 vs. 0% at <4.9 cm2/m2) (P=0.04) and BMI (38.3% at 30-39.9 kg/m2 vs. 0% at <18.5 kg/m2) (P<0.001). In females, 5-year OS increased with BMI (100% at >30 kg/m2) (P=0.05) but not with PMI. Median disease-free survival (DFS) was 2.8 vs. 2.7 years in males and females, respectively (P<0.001). The 5-year DFS was not affected by PMI or BMI in males nor females; 11.1% of patients had major postoperative complications, predicted by squamous cell carcinoma (P=0.03) and stage >Ia (P<0.01). Lower BMI ranges had proportionally more major complications in males (P<0.001), however the opposite was true for females. Mean hospital stay was 4 days longer in males, and doubled with higher BMI [12 days (range, 8-12 days); P=0.76]. BMI and PMI correlated positively in both males (r=0.36, P<0.001), and females (r=0.32, P=0.002). CONCLUSIONS: Radiologically derived PMI is an easily replicable marker which may be a useful adjunct to BMI in identifying high-risk octogenarians in whom prehabilitation may achieve superior outcomes post-surgery for NSCLC. Additionally, the method we describe avoids additional imaging to derive these measurements and can be safely incorporated into pre-operative imaging protocols.