Fractionated dose radiolabeled anti−prostate specific membrane antigen (PSMA) radioimmunotherapy (177Lu−J591) for progressive metastatic castration−resistant prostate cancer (mCRPC).

205 Background: Phase I and II single dose 177Lu−J591 studies have been published. Based on the theoretical advantages of dose fractionation on safety and efficacy, we initiated a phase I dose−escalation study of fractionated−dose 177Lu−J591. Methods: Men with progressive mCRPC with normal neutrophil and platelet counts were enrolled. The initial portion was 3+3 dose−escalation, with 6 cohorts of 3−6 patients receiving 2 doses 177Lu−J591, 2 weeks apart starting with 20 mCi/m2, escalating to 45 mCi/m2. After determining maximum tolerated dose (MTD), patients enrolled in 2 expansion cohorts at recommended phase II doses (RP2D). Planar imaging of 177Lu−J591 at 6−8 days following the initial dose was performed. Pre− and post−treatment PSA was measured for all patients and the highest dose−level cohorts had CTC counts (CellSearch) measured before and after treatment. Results: 48 patients enrolled with median age 74 (55−95) ), median baseline PSA 45.38 (1.93−766.5), 37.5% with prior chemo. The RP2D’s of fractio...