A HER2-targeting antibody-drug conjugate in metastatic breast cancer

New data recently published on Nature Communications shows that a novel HER2-targeting antibody-drug conjugate, FS-1502, is well tolerated and has a promising antitumor activity in HER2+ metastatic breast cancer patients.

This phase 1a/1b trial was designed as a multicenter, single-arm, dose-escalation and dose-expansion study, to investigate safety and efficacy of the HER2-targeting antibody-drug conjugate FS-1502. A total of 150 patients were enrolled and treated at doses from 0.1 mg/kg every 4 weeks to 3.5 mg/kg every 3 weeks; patients with metastatic HER2+ breast cancer received FS-1502 at the recommended phase 2 dose (2.3 mg/kg once every 3 weeks) in phase 1b. After a median follow-up of 5.8 months, one dose-limiting toxicity each was reported at 3.0 and 3.5 mg/kg; the maximum tolerated dose was not reached; five (3.3%) patients experienced pneumonitis, four (2.7%) had grade 3 reversible ocular events. Of 67 HER2-positive breast cancer patients receiving the recommended phase 2 dose, the best objective response rate was 53.7%. Authors cautions that the study has limitations (such as a low initial dose potentially limiting effectiveness and an open label, single-arm design), but conclude that «FS-1502 was well tolerated and demonstrated promising antitumor activity in patients with HER2-positive advanced breast cancer. Further randomized controlled studies with a larger sample size will be needed to confirm the efficacy and safety of FS-1502 in HER2-positive breast cancer. Phase 2 clinical trials with FS-1502 are currently ongoing in various HER2‐positive solid tumor indications».