HER3 has been shown to be overexpressed in brain metastases from breast and non-small lung cancer (NSCLC).2 In a phase I/II trial in patients with metastatic breast cancer, 2 recommended expansion doses (4.8 mg/kg and 6.4 mg/kg) of HER3-DXd were proposed.3 In a phase II study in patients with Epidermal Growth Factor Receptor (EGFR)-mutant NSCLC, other doses were explored. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.