Activity of fractionated radioimmunotherapy (RAIT) with 90Y clivatuzumab tetraxetan (90Y-hPAM4) plus gemcitabine (Gem) in advanced pancreatic cancer (APC): Final results from a two-part study.

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227 Background: A Phase I/II trial was undertaken to evaluate repeated cycles of 90Y-labeled anti-mucin humanized mAb (90Y-hPAM4) plus Gem as first-line therapy in Stage 3-4 APC. Methods: Pts received Gem once-weekly x 4 with 90Y-hPAM4 on wks 2, 3 and 4, with cycles repeated until progression or unacceptable toxicity. In Part I, pts were treated in cohorts with escalating 90Y doses and Gem fixed at a low 200 mg/m2 dose for radiosensitization. In Part II, the Gem doses were increased up to standard levels, with 90Y doses fixed for first cycle, but decreased for subsequent cycles. Tumor responses were assessed by CT, FDG/PET and serum CA19-9; safety by NCI-CTCv3. Results: Of 100 untreated pts enrolled, 10 withdrew early, while 90 (73 stage IV) received 1-4 cycles. In Part I, 38 pts received 90Y-hPAM4 weekly x 3 at 90Y doses of 6.5 (N=4), 9 (N=12), 12 (N=17) or 15 (N=5) mCi/m2, with the same cycle repeated 1-3 times in 13 pts. 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). There were 3 febrile neutropenias, 4 other infections treated with IV antibiotics, but no major bleeding or other AEs. 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 became negative or had >25% SUV reduction, and 33% (9/27) with elevated CA19-9 levels decreased by >50%. The median overall survival was 7.7 mo., but 11.8 mo. for retreated pts [46% (6/13) survived ≥1 yr.], with improved efficacy at higher 90Y doses. In Part II, 52 pts received 12 mCi/m2 90Y-hPAM4 x 3 with Gem doses of 200 (N=17), 600 (N=8) or 1000 mg/m2 (N=27), with 13 pts now retreated at 90Y doses of 6.5 or 9 mCi/m2. Results so far indicate no advantage to giving higher doses of Gem with RAIT. Toxicity, response and survival data for this group will be presented at the conference. Conclusions: Fractionated RAIT with 90Y-hPAM4 combined with low-dose gemcitabine appears to be a manageable and active first-line therapy for APC. It may provide comparable efficacy yet less toxicity compared to other regimens.