Clinical significance of the ‘not otherwise specified’ subtype in candidates for resectable non-small cell lung cancer

The histological subtype of non-small-cell lung cancer (NSCLC) is a significant factor when selecting treatment strategies. However, cases are occasionally encountered that are diagnosed as 'not otherwise specified' (NOS) prior to surgery, due to an uncertain histological subtype. The present study investigated the prognostic significance of the NOS subtype for patients with resectable NSCLC. Between 2001 and 2011, 1,913 patients were diagnosed with NSCLC using transbronchial biopsy and underwent surgical resection at two facilities in Japan. Of these patients, 151 (7.9%) were pre-operatively diagnosed with NSCLC-NOS (NOS group) and the remainder had confirmed histological subtypes (confirmed group). The present study compared the clinicopathological features and prognoses of these groups. Analyses of resected specimens revealed that pleomorphic cell carcinoma, large cell neuroendocrine cell carcinoma, large cell carcinoma and adenosquamous carcinoma were significantly more common in the NOS group than in the confirmed group (P<0.001, P=0.002, P=0.019 and P=0.014, respectively). The five-year survival rate was significantly poorer in the NOS group (60.5 vs. 67.1%; P=0.010), particularly for stage I disease (70.8 vs. 80.7%; P=0.007). The results of a multivariate analysis of overall survival indicated that NOS was a significant independent prognostic factor (hazard ratio, 1.40; 95% confidence interval, 1.02-1.86; P=0.041). These results indicated that pre-operative NOS was significantly associated with poorer survival, including for stage I disease. In conjunction with other clinicopathological parameters, NOS can be a useful prognostic factor when deciding on a treatment strategy for NSCLC.