Background: Controlling nutritional status (CONUT) and skeletal muscle area (SMA) are both useful prognostic factors in patients with non-small cell lung cancer (NSCLC). We hypothesized that low serum creatine kinase (CK) would be a surrogate of decreased SMA, and defined a novel prognostic factor, CONUT/CK score (CNKS). The aim of this study was to elucidate the clinical significance of CNKS in NSCLC patients. Methods: One hundred and eighty-nine patients who underwent surgical resection of NSCLC and whose preoperative computed tomography images were available were enrolled. The CNKS was calculated by summing CONUT score and CK score, which was defined as 0 if the CK concentration is within normal range, and 2 if it is under lower limit. The optimal cut-off values of CNKS and CONUT score were 4 and 2, respectively. Results: Low CK was significantly associated with decreased SMA (P=0.012). The high CNKS group was significantly associated with men and smoking history (P=0.006 and P=0.015, respectively). The high CNKS group had significantly shorter overall survival (OS) and disease-free survival (DFS) (P<0.001 and P=0.003, respectively) than the low CNKS group. The CNKS was found to be an independent prognostic factor for OS and DFS (P=0.012 and P=0.017, respectively), while CONUT score was not. The CNKS was a novel significant predictor of a poor prognosis in patients with NSCLC. Conclusions: The nutritional status combined with skeletal muscle index was suggested to provide more useful prognostic information than alone, which should be investigated in further prospective studies with a larger cohort.
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