Duration of second-line T-DM1 therapy: Is it associated with duration of first-line anti-Her2 therapy in metastatic HER2 + breast cancer?

Abstract

e12512 Background: Tumors with HER2 overexpression usually respond to HER2-targeted therapies. Since the CLEOPATRA and EMILIA trials, a taxane plus trastuzumab and pertuzumab (TTP) are the first-line standard for the management of HER2 + metastatic breast cancer (MBC) and trastuzumab emtansine (TDM-1) is the second-line standard. Intrinsic subtypes existing within HER2+ tumors may impact the degree of a patient’s response to anti HER2 therapy; however HER2 subtyping for predicting response is still experimental and not in routine clinical use. In this retrospective population-based study, we aimed to assess whether duration of treatment (DOT) of second-line TDM1 is associated with the DOT of first-line TTP, and might serve as a hint for a HER2 subtype. Methods: Clalit Health Services (CHS) manages health care of 52% of the Israeli population. We identified 113 HER2+ CHS MBC patients, treated with TTP as first-line treatment that initiated TDM1 as second-line, until Dec. 31, 2016. Patient's (pts) demography, HER2 and HR status were recorded. A Cox proportional hazard model, stratified by HR status, adjusted for age and prior adjuvant trastuzumab, was used to explore the association between second-line and first-line DOT in HR positive and negative pts. Results: Pts baseline characteristics and DOT in first- and second-line treatment are presented in the table. A statistically significant association between DOT of both treatment lines was found in HR positive pts with a trend also in HR negative pts. Conclusions: The observed association between first- and second-line DOT, unrelated to hormonal status, may result from a primary characteristic of the intrinsic tumor subtype, that impacts acquired resistance. Longer observations in larger patient cohorts are required to confirm this observation. [Table: see text]