In lung cancer, the OE was evaluated in small retrospective studies (ranging from 20 to 563 patients) showing HER2 OE (defined as intermediate or high expression, IHC 2+ or 3+) in 18–35% of patients, with a slightly higher prevalence in adenocarcinomas (28–50%) [35,36,37,38,39,40,41]. The gene discussed is ERBB2; the disease is lung cancer.