Radioligand therapy of metastatic prostate cancer using 177Lu-PSMA-617 after radiation exposure to 223Ra-dichloride

Radioligand therapy with Lu-177-PSMA-617 is an innovative and effective therapy for castrate-resistant metastatic prostate cancer patients. For patients with symptomatic bone metastases without visceral metastases, the guidelines recommend radionuclide therapy with Ra-223-dichloride as a single therapeutic agent or in combination with hormone therapy. The aim of this study was to evaluate the safety of repeated cycles of Lu-177-PSMA-617 after exposure to more cycles of Ra-223. Forty-nine patients were treated with three cycles of Lu-PSMA-617 divided into two groups subjected to a history of therapy with Ra-223. Group 1 included 20 patients, who had received therapy with Ra-223 prior to Lu-PSMA-617 therapy. Group 2, which was the control group regarding hematotoxicity, comprised 29 patients without any history of a bone-targeted radionuclide therapy. No CTC 4 degrees hematotoxicity was observed in the entire study population. There was no CTC 3 degrees or CTC 4 degrees leucopenia in either group. One and three patients from group 1 and 2, respectively, showed CTC 3 degrees anemia. In group 1 there was significantly more CTC 2 degrees anemia (50% vs. 6.9%) (p = 0.008). One patient from group 1 (5%) showed a CTC 3 degrees thrombocytopenia without any concurrent anemia, and two patients from group 2 (7%) showed a CTC 3 degrees thrombocytopenia, one with CTC 3 degrees anemia and one without any anemia. There were no significant differences between the two groups regarding leucopenia and thrombocytopenia. These results confirmed that performing repeated cycles of Lu-PSMA-617 after Ra-223 seems to be safe with a very small probability of hematotoxicity.