Abstract P5-21-26: T-DM1 activity in metastatic HER2-positive breast cancer patients who have received prior trastuzumab and pertuzumab: NSABP B-005

Background : The pivotal phase III EMILIA trial reported a progression free survival (PFS) rate of 9.6 months and an objective response rate of 43% with T-DM1 in patients with HER2-positive metastatic breast cancer previously treated with trastuzumab and a taxane. However, there is very limited data on the efficacy of T-DM1 in patients who have received prior pertuzumab either neoadjuvantly or as first line therapy in the metastatic setting. The primary goal of this study was to assess the clinical efficacy (tumor response rates and median duration on therapy) of T-DM1 in patients previously treated with pertuzumab and trastuzumab. Methods: After IRB approval, a cancer data registry and electronic pharmacy database were utilized to identify breast cancer patients receiving treatment with T-DM1 at Cleveland Clinic and University of Pittsburgh. Patients that received trastuzumab and pertuzumab, in either the neoadjuvant or metastatic setting, with baseline and follow up imaging available for review were identified. Patient charts were reviewed to collect accurate information about the treatment sequencing and outcomes. RECIST version 1.1 was utilized for tumor assessment and patients with measurable disease and non measurable disease were included in the study. Results: We identified a total of 23 patients with a median age of 55 years that met the inclusion criteria. 69% percent of patients received T-DM1 as first line or second line therapy and 31% received it as third line or later. All patients had at least 1 measurable lesion. Best overall response showed rates of complete response, partial response and stable disease of 17%, 26% and 22% respectively. 35% patients progressed on first assessment after start of treatment. The median duration on therapy was 5.3 months (range 3 weeks to 33 months) with 43% of patients receiving T-DM1 for greater than 6 months. Conclusion: Our results were comparable to those reported by EMILIA trial. T-DM1 has reasonable clinical efficacy in patients who have received prior treatment with pertuzumab and trastuzumab with an overall response rate of 43% and median duration on therapy of 5.3 months. Citation Format: Tiwari SR, Sussman T, Kota K, Moore HC, Montero AJ, Budd GT, Puhalha S, Abraham J. T-DM1 activity in metastatic HER2-positive breast cancer patients who have received prior trastuzumab and pertuzumab: NSABP B-005 [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-21-26.