In our analysis of 63 HER2-positive early breast cancer patients treated with T-DM1, we found that grade ≥2 thrombocytopenia occurred in 30 (47.6%) patients, and grade ≥3 thrombocytopenia occurred in 16 (25.4%) patients, largely consistent with the results mentioned above. The gene discussed is ERBB2; the disease is breast carcinoma.