Trastuzumab Emtansine Improves pCR Rates in Some Patients With Breast Cancer

Patients with early HER2-positive/hormone receptor (HR)-positive breast cancer who receive neoadjuvant trastuzumab emtansine (T-DM1) with or without endocrine therapy (ET) for only 12 weeks may achieve a clinically meaningful pathologic complete response (pCR), according to a study published in the Journal of Clinical Oncology.¹

Prior studies suggest that T-DM1 may be as effective as current standard therapy — chemotherapy plus anti-HER2 compounds — and has fewer toxic effects.

For this phase 2, prospective trial (ClinicalTrials.gov Identifier: NCT01745965), researchers randomly assigned 375 patients with early HER2-positive/HR-positive breast cancer 1:1:1 to 12 weeks of T-DM1 (3.6mg/kg every 3 weeks for 4 cycles) with or without ET, or to trastuzumab (8mg/kg loading dose, then 6mg/kg every 3 weeks for 4 cycles) with ET.

pCR was confirmed by surgery within 3 weeks of experimental treatment or by histologic confirmation of non-pathologic complete response. Patients also received adjuvant therapy per treatment standards.

pCR, the primary endpoint of the study, was achieved in 41% of patients in the T-DM1 arm, 41.5% in the T-DM1 plus ET arm, and 15.1% in the trastuzumab plus ET arm (P < .001).

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The safety profile was favorable across all 3 treatment arms, but a significantly higher prevalence of grade 1 to 2 adverse events (AEs) was observed in the T-DM1 arms. The most frequently reported AEs in T-DM1 were thrombocytopenia, nausea, and elevation of liver enzymes.

The study authors concluded that “T-DM1 may be an efficient and safe alternative for patients who are not suited for systemic chemotherapy in this setting.”