Phase I/II study of 90Y-clivatuzumab tetraxetan (90Y-hPAM4) combined with gemcitabine (Gem) in advanced pancreatic cancer (APC): Final results

4043 Background: A Phase I/II trial evaluated single and repeated cycles of fractionated radioimmunotherapy (RAIT) with 90Y-labeled humanized mAb (90Y-hPAM4) plus Gem as first-line therapy in Stage 3-4 APC. Methods: Cycles of Gem once-weekly x 4 with 90Y-hPAM4 on wks 2, 3 and 4 were repeated until progression, withdrawal or unacceptable toxicity. In Part I, 90Y doses were escalated with Gem fixed at 200 mg/m2. In Part II, Gem was increased up to 1000 mg/m2, with 90Y fixed at 12 mCi/m2 for cycle 1 and lowered for retreatment. Results: Of 100 pts entered, 10 withdrew early, while 90 (73 stage IV) received 1-4 cycles. In Part I, 38 pts received 90Y-hPAM4 weekly x 3 at 6.5, 9, 12, or 15 mCi/m2, with the same cycle repeated 1-3 times in 13 pts. By CT-RECIST criteria, 6 pts (16%) had PRs and 16 (42%) had stabilization as best response (58% disease control). After cycle 1, 52% (13/25) with PET-avid images had >25% SUV reduction, and 33% (9/27) with elevated CA19-9 levels decreased by >50%. The median OS was 7.7 mo., but 11.8 mo. for retreated pts [46% (6/13) survived ≥1 yr.], and with improved efficacy at higher 90Y doses. NCI-CTCv3 Grade 3-4 platelets or ANC developed in 20/38 (53%) after cycle 1 (all reversible to Grade 1) and in all retreated pts (irreversible in 4/9 pts at 12 or 15 mCi/m2). In Part II, 52 pts received increased Gem without evidence of improved efficacy, while 13 pts were retreated with more acceptable toxicity at lower 90Y doses of 6.5 or 9 mCi/m2. Treatment was well tolerated with no infusion reactions. Infections requiring IV antibiotics occurred at a low rate and responded to appropriate coverage (bacteremia/sepsis, 7%; febrile neutropenia, 4%; ascending cholangitis, 3%; pneumonia, 2%; others 1%). One case of bleeding occurred, due to rectal tumor invasion. Anecdotal reports of good performance and decreased pain medication requirements require further validation. Conclusions: Fractionated RAIT with 90Y-hPAM4 combined with low-dose 200 mg/m2 GEM appears promising as a treatment regimen for APC. Hematologic toxicity was dose limiting. A 90Y-hPAM4 dose of 12 mCi/m2 for cycle 1 and 6.5 mCi/m2 for cycle 2 have been selected as suitable for further clinical development in the first-line setting.