Abstract PS1-03-01: Secondary prevention of cancer therapy-induced thrombocytopenia with hetrombopag in breast cancer: a prospective,multi-center,self-controlled exploratory trial

Abstract Background: Cancer therapy-induced thrombocytopenia (CTIT) is a common complication of anti-tumor therapy and causes treatment delays or interruptions, increased bleeding risk and compromised outcomes. We aimed to evaluate hetrombopag, an oral thrombopoietin receptor agonist that prevented CTIT in breast cancer patients. Methods: In this multi-center, prospective exploratory trial (NCT05394285), breast cancer patients with platelet counts (PLT) < 50×109/L during current anti-tumor treatment cycle (Cycle 1) were enrolled. Those patients were randomized to receive either hetrombopag (7.5 mg daily, n = 30) or subcutaneous recombinant human thrombopoietin (rhTPO, 15000 U daily, n = 30) until their PLT >100×109/L, which was defined as the thrombocytopenia treatment phase (TTP). Eligible patients were scheduled to continue the same anti-tumor regimen in their subsequent treatment cycle (Cycle 2). The secondary prevention phase (SPP) was initiated using a self-controlled design, with prophylactic hetrombopag (7.5 mg/day for 14 days) administration beginning one day after the start of Cycle 2. The primary endpoint was the response rate during the SPP, defined as the proportion of patients meeting all predefined criteria before the next treatment cycle (Cycle 3): 1. no platelet transfusion requirement; 2. no anti-tumor treatment modification (≥20% dose cut, ≥5 days delay, or discontinuation) ; 3. absence of severe thrombocytopenia (PLT