Thero2-01S22 in HER2-positive Breast Cancer

This study is a two-part, multicenter, randomized, double-blind, placebo-controlled, Phase III trial. Part 1 will confirm the recommended Phase III dose of Thero2-01S22 when administered as add-on therapy on top of first line anti-HER2 targeted treatment of patients with metastatic breast, with the aim to obtain about 15 evaluable participants in Thero2-01S22 group and 15 in the placebo group. Part 2 will assess the efficacy of Thero2-01S22 treatment at the recommended dose when administered as add-on therapy on top of first line anti-HER2 targeted treatment of patients with metastatic breast. Approximately 290 participants will be randomized to receive Thero2-01S22 or Thero2-01S22 matching-placebo in combination with trastuzumab and pertuzumab. Participants in both Part 1 and Part 2 will receive induction therapy according to local practice with a taxane (docetaxel, paclitaxel, or nab-paclitaxel) or vinorelbine for 4 to 6 cycles in combination with pertuzumab and trastuzumab.