Cardiac safety, efficacy, and correlation of serial serum HER2-extracellular domain shed antigen measurement with the outcome of the combined trastuzumab plus CMF in women with HER2-positive metastatic breast cancer: results from the EORTC 10995 phase II study

Cardiotoxicity is a side effect of trastuzumab. We assessed efficacy and cardiac safety of CMF with trastuzumab (CMF+T) in HER2-positive metastatic breast cancer patients (MBC). In this phase II study, centrally confirmed, previously treated HER2-positive MBC patients with measurable disease (per RECIST v 1.0) were enrolled. Initially, patients were randomized between 8 CMF cycles alone or combined with trastuzumab during chemotherapy, followed by 3-weekly trastuzumab maintenance till progression. A protocol amendment dropped the CMF arm and thereafter all patients received CMF+T. Translational research for prediction of treatment benefit was performed through serial serum HER2-shed antigen assessments. Ninety patients (CMF: 19; CMF+T: 71) were enrolled between 2002 and 2006. Median age was 54 years. 42 patients had prior chemotherapy (33 with anthracyclines) and 41/71 patients who received CMF+T continued trastuzumab monotherapy for a median duration of 40 weeks. Overall response rate was 50% for CMF+T (35/70) and 32% for CMF (6/19). Median duration of response was 10.3 months and 5.4 months, respectively. Median progression-free survival was 9.4 months (95% CI 8.1-11.6) and 4.8 months (95% CI 2.8-7.9), respectively. In the CMF+T arm, 13(18%) patients had an absolute LVEF decline, including 3 patients developing any grade of New York Heart Association cardiac dysfunction. Patients with an increase of 30% over baseline shed antigen had a higher progression risk (95% CI 7.6, 3.9-14.8). CMF+T is effective, with an acceptable cardiotoxicity profile. LVEF declines were mostly asymptomatic and occurred irrespective of previous anthracycline exposure. CMF+T can be considered for these patients, if other cytotoxics are contraindicated.