Peripheral but not axial muscle mass is associated with early mortality in bone metastatic lung cancer patients at diagnosis.

Identification of sarcopenia is a key issue in oncology. Several methods may be used to evaluate muscle mass in patients. Routine cancer follow-up computed tomography (CT) provides axial muscle mass whereas whole-body densitometry (DEXA) measures appendicular lean mass (ALM). Up to now, no studies have assessed, in cancer patients, the correlation between CT and DEXA muscle mass indicators and compared their prognostic value. We included patients with synchronous bone metastases from lung adenocarcinoma at diagnosis. Diagnosis was confirmed by bone biopsy. Skeletal muscle area was determined semi-automatically on initial CT scan at the T7, T12, and L3 vertebral level using Osirix® software. The skeletal muscle index (SMI) was calculated as the ratio of muscle area to height squared. Standardised ALM/height squared data were obtained by DEXA assessment within a 30-day window of CT. A total of 65 patients were included; 47 (72%) were male. Mean±SD age was 65±11.4years. DEXA was available for 46 patients. The performance status was good (<1) for 39 patients. SMI indicators were significantly correlated with each other (rho from 0.3 to 0.7) but moderately correlated with ALM (rho from 0.1 to 0.7). ALM had a good discriminatory ability on 6-month survival (AUC 0.87 [0.76; 0.97]). ALM was associated with early mortality (<6months) (HR=0.29, 95% CI [0.15; 0.57]; P<0.001) but not with later mortality (>6months). In contrast, no significant effect was found for SMI. Peripheral muscle mass (standardized ALM by DEXA) but not axial muscle mass (SMI assessed by CT) was associated with early mortality (<6months) suggesting that cancer-induced muscle loss would affect differently appendicular muscles and axial muscles.

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