Abstract P4-14-04: A chart review of patient characteristics, treatment patterns and response in metastatic breast cancer patients treated with ado-trastuzumab emtansine in first-line therapy and beyond
Authors: Gauthier G , Guerin A , Zhdanava M , Wu E , Masaquel A , Barnett B 
Published: May 2016

Background: Ado-trastuzumab emtansine (T-DM1) approved for HER2+ unresectable locally advanced metastatic breast cancer (mBC) has been shown to significantly improve progression-free and overall survival in patients (pts) previously treated with trastuzumab and a taxane. However, little is known about real-world patterns and outcomes of T-DM1.

Method: Pt-level data was collected from 90 US oncologists using an online chart extraction tool. Oncologists randomly selected eligible adult mBC pts started on T-DM1 on or after February 22nd 2013. Pts demographics, clinical information, and T-DM1 patterns and responses were described. Among pts whose T-DM1 response was assessed, univariate logistic regression models were used to assess the association between each factor and the probability of achieving complete response (CR).

Results: Among the 303 pts, median follow-up after T-DM1 initiation was 5.1 months; 58.4% started T-DM1 in the 2nd half of 2014. Median age was 58 years, most pts were Caucasian (62.0%), median number of metastatic sites was 2, and 65.3% of pts had a mBC diagnosis (dx) within 1 year of the BC dx. Most common metastatic sites were liver (51.5%), lung/pleura (42.6%), and bone/bone marrow (41.6%). Median time from mBC dx to T-DM1 initiation was 7.1 months. 34.0% of pts started T-DM1 in 1st line for mBC, 55.4% in 2nd line, and 10.6% in later lines after mBC dx; most common prior treatments were trastuzumab, pertuzumab, and taxane. Best response achieved while on T-DM1 was CR in 17.5% of pts, partial response (PR) in 46.2%, stable disease in 11.2%, recurrence/progression in 3.6%, and the response was unknown in 21.5% of pts. CR/PR was achieved within a median of 5 months of T-DM1 initiation. At the end of follow-up, 80.2% were still on T-DM1, 3.3% had switched, 12.9% had discontinued without switching, and 3.6% were deceased. 44.9% of pts discontinued/switched after CR/PR and 32.7% after progression. When physicians were surveyed about their practice, 30.0% reported intention to interrupt T-DM1 after CR and 7.8% after an a priori determined number of cycles. Among pts whose response on T-DM1 was assessed (78.5%), race (Asian), initiation of T-DM1 shortly after mBC dx or in 1st line for mBC, ≤ 2 metastatic lesions, single metastatic site, and estrogen (ER)+ /progesterone (PR)+ at T-DM1 initiation were found to be significant predictors of CR, while pts who progressed between mBC dx and T-DM1 were less likely to achieve CR.

Table 1. Factors Associated with CR Odds Ratio and 95% Confidence IntervalsAsian (vs non-Asian)2.9 (1.2 - 7.4)T-DM1 ≤ 1 year after mBC dx (vs &gt; 1)3.2 (1.4 - 7.6)T-DM1 in 1st line after mBC dx (vs later lines)3.8 (2.0 - 7.2)≤ 2 metastases (vs&gt;2)3.8 (1.9 - 7.6)1 metastatic site (vs &gt;1)4.4 (2.3 - 8.4)ER+/PR+ (vs other status)4.9 (2.5 - 9.7)Progression between mBC dx and T-DM1 (vs no progression)0.2 (0.1 - 0.4)

Conclusions: Most pts started T-DM1 as 1st or 2nd line therapy for mBC and were still treated with T-DM1 at the end of follow-up. CR/PR, assessed by treating oncologists, was achieved in &gt;50% of pts within 5 months of T-DM1 initiation.

Citation Format: Gauthier G, Guerin A, Zhdanava M, Wu E, Masaquel A, Barnett B. A chart review of patient characteristics, treatment patterns and response in metastatic breast cancer patients treated with ado-trastuzumab emtansine in first-line therapy and beyond. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-14-04.