In HER2CLIMB, a phase II clinical trial, tucatinib–trastuzumab–capecitabine combination therapy for HER2-positive breast cancer showed a higher ORR and median PFS than the placebo–trastuzumab–capecitabine group (Table 1); however, this was associated with a high incidence of adverse effects [56]. The gene discussed is ERBB2; the disease is breast carcinoma.