FS-1502 demonstrated encouraging antitumor activity, with the best ORR of 53.7% and median PFS of 15.5 months (95% CI, 4.6-not reached) for patients with HER2-positive breast cancer at the RP2D of 2.3 mg/kg Q3W, with the median DOR and OS not yet reached due to short follow-up. This evidence concerns the gene ERBB2 and breast carcinoma.