Investigation of Thrombocytopenia Associated with Trastuzumab Emtansine Treatment in Breast Cancer: A Retrospective Study in a Chinese Population.

Purpose: Thrombocytopenia is a common adverse event associated with trastuzumab emtansine (T-DM1) treatment in patients with HER2-positive metastatic breast cancer. This study aims to evaluate the incidence, clinical characteristics, and risk factors of T-DM1-associated thrombocytopenia.

Patients and methods: This retrospective study included patients with breast cancer who received T-DM1. Thrombocytopenia was defined as a platelet count of less than 100 × 10⁹/L. Potential risk factors for thrombocytopenia were analyzed.

Results: The study cohort consisted of 47 patients with a median age of 55 years, including one male patient. Thrombocytopenia was observed in 74.5% of patients during T-DM1 treatment. A total of 63.3% of patients with Ki-67 expression levels ≥30% experienced thrombocytopenia, which was significantly lower than the 94.1% incidence in patients with Ki-67 expression <30% (P=0.034). Patients with completed or ongoing T-DM1 treatment had a thrombocytopenia incidence of 90.5%, compared to 64% in those who discontinued treatment (P=0.036). Although not reaching statistical significance, concurrent radiotherapy was associated with a higher incidence of thrombocytopenia (87.5%). After appropriate interventions, 70% of patients showed restored platelets, while 17.1% required dose reductions.

Conclusion: Thrombocytopenia is a prevalent adverse event during T-DM1 treatment in real-world practice. An increased incidence with concurrent radiotherapy was observed. While the incidence of thrombocytopenia appears to rise with prolonged exposure in completed or ongoing T-DM1, it may have a minor impact on the overall duration of therapy. Future studies should examine these findings to guide prophylactic strategies and interventions for high-risk patients.