A phase-Ib study of TRK-950 combined with anticancer treatment regimens in patients with gastric and gastro-esophageal junction (GEJ) cancer.

361 Background: TRK-950 is a first-in-class humanized antibody raised against CAPRIN-1 which we have identified as a novel and universal target for cancer therapies. TRK-950 strongly and specifically binds to various cancer cells and shows anti-tumor effects via engagement of immune cells. A series of pre-clinical studies demonstrates its potency and safety. In the phase I study of TRK-950 monotherapy (NCT02990481), it appears safe and well tolerated. No DLT was observed and MTD was not reached at doses of 3-30mg/kg IV weekly. Here, we report on select cohort of the ongoing, multicenter phase Ib study of TRK-950 combined with standard of care (SOC) regimens in patients (pts) with gastric cancer including GEJ cancer (NCT03872947). Methods: Patients with gastric or gastro-esophageal junction (GEJ) cancer and measurable disease were enrolled in phase Ib study, and received paclitaxel on D1, 8, 15 and ramucirumab on D1, 15 of 28-day cycles. In addition TRK-950 was given 10 mg/kg IV weekly. DLT was evaluated during the first cycle. Response was assessed every 2 cycles up to Cycle 6 and every 3 cycles thereafter. Primary endpoint was safety and tolerability. Secondary endpoints included overall response rate (ORR), disease control rate (DCR) per REClST v1.1. Tumor CAPRIN-1 expression was retrospectively assessed by IHC. Results: Nine patients were enrolled, median age 58 yrs; Karnofsky performance status 80 (11%), 90 (67%), 100 (22%); 89% male, 11% female; median number of prior treatments 2 [1, 4]. TRK-950 in combination with ramucirumab and paclitaxel was well tolerated with no DLTs. Most common all-grade treatment-related AEs (TRAEs) were fatigue (67%), vomiting (33%), anemia (22%), nausea (22%), diarrhea (22%), neutrophil count decreased (22%) and decreased appetite (22%). Most common grade ≥ 3 TRAE in ≥ 20% of pts were anemia (22%) and neutrophil count decreased (22%). In 9 response-evaluable pts, ORR was 55.6% and DCR was 100%. Four patients had a screening CAPRIN-1 score of 3+, and all achieved partial response. Conclusions: TRK-950 binds to a newly described target, CAPRIN-1, and has an acceptable safety and tolerability profile when combined with ramucirumab and paclitaxel in gastric cancer including GEJ cancer. Preliminary clinical activity is demonstrated in pre-treated patients with encouraging response rates, particularly enriched by the expression of CAPRIN-1. Further antitumor activity is being confirmed by limiting patients to only 1 prior treatment regimen with an eye towards a randomized trial. Clinical trial information: NCT03872947 .