ALK-rearranged lung adenocarcinoma, comprising 4‒5% of lung adenocarcinomas, is clinicopathologically characterized by a TTF-1 cell lineage, an acinar structure with mucin/signet-ring cell morphology, non-/light-smoking history, and young onset [32,33,34,35]. The gene discussed is MUC5AC; the disease is lung adenocarcinoma.