As of 20 Jul 2020, 137 pts had received talquetamab; 102 by IV (0.5 – 180 µg/kg) and 35 by SC (5 – 800 µg/kg) dosing. Median age was 64 years (33 – 80; 31% were ≥70) and 22% had ISS stage III disease at study entry. Median number of prior therapies was 6 (2 – 20) over a median of 6.5 years (0.9 – 27) since diagnosis, 85% were refractory to last line of therapy, 79% triple-class refractory, 73% penta-drug exposed, and 31% penta-drug refractory. 13 (10%) pts had received selinexor and 21 (15%) had prior BCMA-directed therapy.

Most frequently reported all grade AEs were anemia (50%), CRS (47%), neutropenia (45%), and lymphopenia (40%). Most common grade 3 – 4 AEs were lymphopenia (37%), anemia (27%), and neutropenia (25%). CRS was mostly grade 1 – 2 except for 5 pts with grade 3 CRS (˂8% of pts with CRS) that occurred with IV dosing; only grade 1 – 2 CRS was seen with SC dosing. CRS was generally confined to the first cycle with median time to onset of 1 day (1 – 3) for IV and 2 days (1 – 5) for SC dosing. Treatment-related neurotoxicity was reported in 7 (5%) pts (all resolved/resolving; median duration of 2 days [1 – 9]): 4 had grade 1 – 2 events and 3 had grade 3 events of delirium (n=1), decreased level of consciousness (n=1), or confusion (n=1). Six of 7 pts had neurotoxicity that occurred in the context of CRS, including all 3 grade 3 events. Infections were reported in 37% of pts (8% grade 3 – 4). Infusion related reactions (IV; 15%) and injection site reactions (SC; 14%) were grade 1 – 2 and generally occurred in cycle 1. Two dose-limiting toxicities were observed: clinically asymptomatic grade 4 increased lipase in the setting of a pancreatic plasmacytoma (7.5 µg/kg IV) and grade 3 maculopapular rash (135 µg/kg SC). The maximum tolerated dose (MTD) has not been defined.

Overall response rate (ORR) for IV doses of 20 – 180 µg/kg was 78% (14/18; 2 pending confirmation); 6/6 responded at the 60 µg/kg IV dose. ORR for SC doses of 135 – 405 µg/kg was 67% (8/12); 3/4 responded at the 405 µg/kg SC dose. Responses were noted starting at 1.0 µg/kg, were rapid at a median of 1 month (0.2 – 3), and durable with median not reached in 36/46 (4 pts with response 15+ months; longest at 23+ months). Data at higher doses are immature, and results will be updated at the meeting.