Background: T-DM1 was approved for pts with HER2+ MBC previously treated with trastuzumab (H) and a taxane based on the phase III EMILIA study. P in combination with H + docetaxel (T) later became the first-line standard of care for HER2+ MBC, but there are limited data on T-DM1 efficacy in pts who previously received P. We present exploratory efficacy results from pts treated with T-DM1 any time after P from 2 phase III studies: CLEOPATRA and PHEREXA. Methods: CLEOPATRA (NCT00567190) and PHEREXA (NCT01026142) are randomized, 2-arm trials evaluating P-based regimens for HER2+ MBC. CLEOPATRA studies H + T + P vs HT + placebo in pts with no prior anti-HER2 treatment (tx) or chemotherapy for MBC, while PHEREXA studies H + capecitabine (C) +/− P in pts who progressed during/after previous H tx for MBC. We assessed overall survival (OS) in an exploratory analysis of pts who either received or did not receive T-DM1 at any time after discontinuing study-assigned tx in CLEOPATRA or PHEREXA. Results: Of 408 pts who received HTP in CLEOPATRA and 228 pts who received HCP in PHEREXA, 32 and 43 pts received subsequent T-DM1, respectively (Table). Median duration of T-DM1 tx was 7.1 mo (range 0−44) and 4.2 mo (range 0−22), respectively, and median time from discontinuation of P to start of T-DM1 was 3.5 mo (range 1−47) and 10.6 mo (range 1−28). Conclusions: Although data are limited in these exploratory analyses, our results provide additional evidence of T-DM1 clinical activity in pts with HER2+ MBC who progressed on prior P + H, a finding with real-world implications. Clinical trial information: NCT00567190, NCT01026142

^avs no T-DM1. ^bLog-rank P-value. HR, hazard ratio; NR, not reached.