The analysis of both gene isoforms on mRNA level in NSCLC samples revealed significantly higher expression of STAT5B isoform as compared with STAT5A. It might suppose different functions for both isoforms also in lung cancer cells, i.e., in result, different downstream target genes (including oncogenes) specifically induced by either STAT5A or STAT5B. The gene discussed is STAT5B; the disease is non-small cell lung carcinoma.