Trastuzumab Single-Drug Therapy after Failure of Cytotoxic Treatment for Metastatic Breast Cancer

Background: Trastuzumab is an established component of breast cancer combination regimens, but data on the safety and efficacy of single-agent therapy is sparse. Patients and Methods: 70 patients with HER2-overexpressing breast cancer after failure of at least one chemotherapy regimen for metastatic disease were recruited from 28 institutions. HER2 overexpression was 3+ in 96% and 2+/FISH+ in 4%. Treatment consisted of a loading dose of 4 mg/kg trastuzumab in the first week and 2 mg/kg per week there-after, continued until progression. Results: Trastuzumab treatment duration ranged from 1 to 66 weeks (median: 12). Objective responses (complete response (CR)/partial response (PR)) were seen in 12/62 fully evaluable patients (19%; 2 CR) while another 29% showed stabilization of the disease. Half of the patients had experienced progression after 13 weeks while median duration of response reached 44 weeks. Median survival was 68 weeks with nearly one-third of the patients still alive after more than 3 years. The most frequent adverse reaction was infusion-related syndrome arising during the first administration. Significant cardiovascular problems were detected in 3 cases, all with anthracycline pretreatment. Conclusions: Patients with metastatic breast cancer overexpressing HER2 may benefit from trastuzumab single-drug treatment, predominantly due to its favorable safety profile.