Abstract CT084: Long-term exposure (LTE) to Tislelizumab, an investigational anti-PD-1 antibody, in a first-in-human Phase I study

Background Tislelizumab (BGB-A317), an investigational monoclonal antibody with high affinity and specificity for PD-1, was engineered to minimize binding to FcγR on macrophages in order to abrogate antibody-dependent phagocytosis, a potential mechanism of resistance to anti-PD-1 therapy. Previous reports from early phase studies suggest tislelizumab was generally well tolerated and had antitumor activity in patients (pts) with advanced solid tumors. Clinical effects of tislelizumab LTE (>12 mo) in pts enrolled in the first-in-human study (NCT02407990) are presented here. Methods Patients with advanced solid tumors received IV tislelizumab 0.5, 2, 5, or 10 mg/kg Q2W, 2 or 5 mg/kg administered Q2W or Q3W, or 200 mg IV Q3W. Antitumor activity was assessed by RECIST v1.1 criteria; PD-L1 expression was retrospectively assessed with the VENTANA PD-L1 (SP263) assay. Results As of 31 Aug 2018, 63 of the 451 pts received tislelizumab for >12 mo. In these 63 pts, median age was 64 yr and 70% had received ≥1 prior systemic therapy. Tislelizumab LTE was most common in NSCLC (n=9), HCC (n=7), and bladder and ovarian (n=5 each) cancers. Four of the 5 pts who achieved CR during this study had LTE to tislelizumab (Table); all 4 pts were PD-L1+ (≥1% expression on tumor cells). Across the LTE cohort, ORR was 66.7%; PR and SD were observed in both PD-L1+ and PD-L1- tumors. The median time to CR/PR (3.7 mo) and duration of CR/PR (21.1 mo) were longer in pts with LTE than pts who responded but did not remain on treatment for >12 mo (2.1 and 6.3 mo, respectively). Rash was the only treatment-related AE (TRAE) reported in ≥15% of pts. Most TRAEs were of mild or moderate severity; arthritis, diarrhea, fatigue, granuloma, hyperglycemia, and lichenoid keratosis (n=1 each) were the only grade ≥3 TRAEs reported with tislelizumab LTE. Conclusion Tislelizumab remained well tolerated for >12 mo and elicited durable responses in pts with a variety of tumor types regardless of PD-L1 status. Citation Format: Jayesh Desai, Benjamin Markman, Michael Friedlander, Hui Gan, Lisa Horvath, Amanda Townsend, Michael Millward, Michael Jameson, Chia-Jui Yen, Ming-Mo Hou, Jeannie Hou, John Wu, Liang Liang, Sanjeev Deva. Long-term exposure (LTE) to Tislelizumab, an investigational anti-PD-1 antibody, in a first-in-human Phase I study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT084.