Early thrombocytopenia predicts longer time‑to‑treatment discontinuation in trastuzumab emtansine treatment.

Thrombocytopenia is a characteristic adverse event of trastuzumab emtansine (T-DM1), one of the essential treatment options for human epithelial growth factor receptor 2 (HER2)-positive breast cancer. The present study investigated the predictive value of thrombocytopenia for time-to-treatment discontinuation (TTD) in patients receiving T-DM1 for advanced-stage HER2-positive breast cancer. The present observational study enrolled 138 patients who received T-DM1 at six oncology centers from January 2016 to December 2021. Univariate and multivariate Cox regression analyses were performed to determine the factors affecting TTD. The median age of patients was 50 years (range, 26-83). The median number of T-DM1 cycles was 9 (range, 2-58), the overall response rate was 50.0% and the disease control rate was 69.6%. At a median follow-up time of 19.3 months, the median TTD was 9.5 months [95% confidence interval (CI), 7.3-11.7], and the median overall survival was 28.2 months (95% CI, 19.2-37.2). Thrombocytopenia during treatment was observed in 39% of all patients, and 66.7% of these patients experienced early thrombocytopenia (in the first four treatment cycles). Multivariate analysis revealed that the independent factors for TTD were hormone receptor status [hazard ratio (HR), 1.837; 95% CI, 1.249-2.701; P=0.002], Eastern Cooperative Oncology Group performance status score (HR, 3.269; 95% CI, 1.788-5.976; P<0.001) and thrombocytopenia during treatment (HR, 0.297; 95% CI, 0.198-0.446; P<0.001). Patients with early thrombocytopenia had a significantly longer TTD of 17.3 months (95% CI, 11.8-22.8) compared with 7.6 months (95% CI, 5.8-9.4) for patients without early thrombocytopenia (P<0.001). The results of the present study indicated that patients with early thrombocytopenia had improved survival outcomes compared with those without. Thus, maximum benefit from T-DM1 treatment may be achieved by confirming the predictive role of thrombocytopenia in T-DM1 treatment in prospective studies and large-scale cohorts.