Purpose: Up to 30% of patients with castration-resistant prostate cancer (CRPC) do not show any response to the first cycle of radioligand therapy (RLT) with [177Lu]Lu-PSMA-617 (Lu-PSMA). We evaluated patient response to the second and third cycles of RLT in patients that underwent at least three cycles. The second aim of this study was to calculate the median overall survival (OS) of responders and non-responders after the first cycle and after all three cycles of RLT.
Methods: CRPC patients were treated with Lu-PSMA, with a median interval of 8 weeks between each cycle. The tumour marker prostate-specific antigen (PSA) was used as the marker for response evaluation.
Results: Fifty-two patients underwent a total of 190 cycles of RLT (3-6 cycles per patient). Of these, 80.8% showed a decline in PSA 2 months after the first cycle, with 44.2% showing a PSA decline of ≥50%. When compared to baseline PSA, 73.1% showed a PSA decline after the third cycle. 50% of patients that did not show any response to the first cycle also did not respond to the second and third cycles. The median OS was 60 weeks in all patients. The median OS was significantly longer for patients that showed any PSA decline after the first cycle compared to patients without PSA decline (68 vs. 33 weeks). There was a significant difference in median OS between responders and non-responders for a change in PSA after the third cycle compared to baseline PSA.
Conclusion: Patients with a positive response to RLT, regardless of the rate of decline, had a significantly longer median OS. Of the patients that did not show any response to the first cycle, 50% responded to the second or third cycles.
Keywords: 177Lu; Overall survival; Prostate cancer; Prostate-specific membrane antigen; Response.