T-DM1 in Previously Treated HER2+ Metastatic Breast Cancer

Denise A. Yardley, MD

An analysis of the T-PAS expanded access study of trastuzumab emtansine (T-DM1) in previously treated HER2+ metastatic breast cancer (MBC) confirmed existing information on the safety of the combination, and observed significant clinical activity in a patient population that averaged seven prior therapies. The analysis was presented at the 2013 Breast Cancer Symposium, held September 7-9 in San Francisco, California.

The study enrolled 215 HER2+ (IHC 3+ or FISH/CISH+) patients with locally advanced or MBC and left ventricular ejection fraction (LVEF) ≥ 50%. All of the patients, who received 3.6 mg/kg of T-DM1 every 3 weeks, had already been treated with an anthracycline and a taxane as well as capecitabine or 5-FU and ≥2 HER2-directed agents (including trastuzumab and lapatinib).

At baseline, the median LVEF was 60%, and 50% of patients had investigator-reported cardiovascular disease

The median follow-up was 5.9 months; median T-DM1 duration was 5.0 months, with 15.8% receiving >18 cycles. Objective response rate, as assessed by investigators on day 1 of every cycle, was 25.6%.

The rate of ≥ grade 3 adverse events was 43.7%, and rate of serious adverse events of any grade was 18.1%. The most common ≥ grade 3 adverse events were thrombocytopenia (7.9%), fatigue (4.7%), and increased aspartate aminotransferase and anemia (3.7%). Cardiac dysfunction (primarily asymptomatic decreases in LVEF) of any grade occurred in eight patients and of ≥ grade 3 in four patients. There were no ≥ grade 3 bleeding events.