A Randomized Phase I Study of Abemaciclib in Chinese Patients with Advanced and/or Metastatic Cancers

BACKGROUND: Abemaciclib, a cyclin-dependent kinase 4 and 6 inhibitor, is approved in combination with endocrine therapy or as monotherapy for hormone receptor-positive and human epidermal growth factor receptor-2-negative (HR+/HER2−) advanced breast cancer outside of China. OBJECTIVE: To evaluate the safety, tolerability, and pharmacokinetic (PK) profile of abemaciclib in Chinese patients with advanced and/or metastatic cancers. PATIENTS AND METHODS: A multicenter, open-label, phase I trial of abemaciclib in Chinese patients with advanced and/or metastatic cancers was conducted. Patients were randomized (1:1) to oral abemaciclib 150 or 200 mg every 12 h on a 28-day cycle. Safety analyses (primary outcome) included all patients receiving at least one dose of abemaciclib. PK and antitumor activity were also assessed. RESULTS: Of the 26 patients randomized, 25 received abemaciclib 150 mg (n = 12) or 200 mg (n = 13). All 25 patients reported ≥ 1 treatment-emergent adverse event (TEAE). The majority of TEAEs were Common Terminology Criteria for Adverse Events (CTCAE) Grade 1 or 2 in severity. The most frequent TEAEs of Grade ≥ 3 were neutropenia (32%) and thrombocytopenia (24%). Four patients (16%) discontinued treatment due to AEs. Abemaciclib exhibited slow absorption and clearance at single dose, with maximum concentrations achieved after around 6 h and an elimination half-life of approximately 24 h. No complete response was observed, two patients (8%) achieved partial response, with one confirmed responder, and the disease control rate was 68% (n = 17). CONCLUSIONS: Abemaciclib was well tolerated and the safety and PK profiles in Chinese patients were comparable to those previously reported in non-Chinese populations. Preliminary antitumor activity was observed. CLINICALTRIALS.GOV IDENTIFIER: NCT02919696.