Real-world effectiveness of post-T-DM1 treatments in HER2-positive metastatic breast cancer: KBCSG-TR1917 observational study.

Abstract

e13020 Background: For patients with HER2-positive, unresectable and/or metastatic breast cancer (HER2+ mBC), T-DM1 is now the standard of care after trastuzumab and/or pertuzumab-based therapy. On the other hand, there is limited evidence after T-DM1 treatment. To clarify the treatment options and the effectiveness of drug therapy just after T-DM1 (post–T-DM1 therapy), we performed a multicenter observational study in patients with HER2+ mBC. Methods: This study enrolled consecutive patients who met eligibility criteria; Japanese female patients with HER2+ mBC, 20 years of age or older, who received at least one subsequent drug treatment except for an investigational drug after discontinuing T-DM1 between Jan 2014 and Dec 2018. To investigate the effectiveness of post–T-DM1 therapy, the real-world progression-free survival (rwPFS), time to treatment failure (TTF), overall survival (OS), objective response rate (ORR) and clinical benefit rate (CBR) were evaluated. Tumor response was exactly assessed by investigators according to RECISTv1.1. Results: Of 205 patients who were treated with T-DM1 at five institutions, 138 patients were enrolled and 128 patients were included in the analysis (data-cut off: Jul 31 2019). The median age of the patients was 59 years (range 27–84), and the median duration of T-DM1 treatment was 5.1 months (range 0.0–41.4). Ninety-two patients (71.9%) had an ECOG PS score of 0 or 1. Of the 128 patients, 34 (26.6%) patients received lapatinib + capecitabine therapy, 35 (27.3%) trastuzumab-based therapy (excluding pertuzumab), 36 (28.1%) pertuzumab-containing therapy, and 23 (18.0%) other therapy except for anti-HER2 therapy. In the 111 patients with measurable lesions, ORR was 22.5% (95% CI: 15.1–31.4). The median rwPFS was 5.7 months (95% CI: 4.8–6.9), median TTF 5.6 months (95% CI: 4.6–6.4), median OS 22.8 months (95% CI: 18.2–32.4), and the CBR was 47.7% (95% CI: 38.8–56.7) in the 128 patients. Conclusions: We clarified that the effectiveness of post–T-DM1 therapy was limited among the current standard treatment options. Therefore, to improve the prognosis in the later settings of HER2+ mBC, novel treatment options are warranted in the future. Clinical trial information: UMIN000038296 .