Our aim is to characterize the frequency and phenotypic distribution of actionable pharmacogenes in Brazilian patients with metastatic prostate cancer (MPC) and Human Epidermal Growth Factor Receptor 2 (HER2)-positive breast cancer (BC).<h4>Methods</h4>This analysis included 452 patients (259 BC, 193 MPC) from a multicenter study across 19 Brazilian sites. The gene discussed is ERBB2; the disease is metastatic prostate carcinoma.