An important feature that differentiates CCTL from other types of lung cancer, such as metastatic clear cell tumors or other clear cell tumor variants, is the presence of immunoreactivity for CD10, CK, and EMA.20, 21 CK positivity is a characteristic of both primary and secondary clear cell adenocarcinomas of the lung.13 In our case, the diagnosis was based on the typical histological picture of the tumor: positivity for CD10, vimentin, pan‐cytokeratin MNF116, and CK7, and negative for TTF‐1. The gene discussed is TTF1; the disease is lung cancer.