T-DM1 activity in metastatic HER2-positive breast cancers that received prior therapy with trastuzumab and pertuzumab.

585Background: Ado-trastuzumab emtansine (T-DM1) is currently approved for patients with trastuzumab-resistant HER2-positive metastatic breast cancer (MBC). However, there is no data on the activity of T-DM1 in patients who received prior pertuzumab, now included as standard first line therapy. The goal of this study was to assess the efficacy of T-DM1 in routine clinical practice in a contemporary patient population that received prior trastuzumab and pertuzumab. Methods: We identified all patients with HER2-positive MBC who received T-DM1 after trastuzumab and pertuzumab between March 1, 2013 and July 15, 2015 through electronic pharmacy records and departmental databases at 3 institutions, MD Anderson Cancer Center, Smilow Cancer Hospital at Yale and The James Cancer Hospital at the Ohio State University. We reviewed the medical records of each case to confirm treatment sequencing and outcome. Results: Eighty-two patients were identified and 78 were available for outcome analysis; 32% received T-DM1 as...