A small retrospective Spanish study [33] of 15 real‐world patients with metastatic HER2+ breast cancer found the most common AEs to be elevated transaminases (73.3%), thrombocytopenia (53.4%), anemia (46.6%), neutropenia (46.6%), and hypokalemia (46.6%). The gene discussed is ERBB2; the disease is Decreased total neutrophil count.