In a phase II trial (N = 15), heavily pretreated patients with NSCLC harboring HER2 exon 20 mutation or overexpression were treated with T-DM1; the ORR, mPFS, and mOS were 6.7% (CI 0.2–32.0), 2.0 months, and 10.9 months, respectively. The gene discussed is ERBB2; the disease is non-small cell lung carcinoma.