To validate the disproportionate expression levels between NKX2‐1/TTF‐1 exon 1 and exon 4/5 observed in FFPE tumour tissues, expression of both NKX2‐1/TTF‐1 exon 1 and exon 4/5 was evaluated in a panel of 10 lung cancer cell lines, consisting of six EGFR‐mutated and four KRAS‐mutated cell lines. The gene discussed is NKX2-1; the disease is lung cancer.