Influence of short-term dexamethasone on the efficacy of 177Lu-PSMA-617 in patients with metastatic castration-resistant prostate cancer

Abstract

Background and Aim: Corticosteroids alone or in combination therapy are associated with favorable biochemical responses in metastatic castration-resistant prostate cancer (mCRPC). We speculated that the intermittent addition of dexamethasone may also enhance the antitumor effect of radioligand therapy (RLT) with 177Lu-prostate-specific membrane antigen (PSMA)-617. Patients and Methods: Seventy-one patients with mCRPC were treated with 1 to 5 cycles of 177Lu-PSMA-617 (6.0-7.4 GBq per cycle) at 6 to 8 weeks intervals. Based on the clinical decision (eg, in the case of vertebral metastases), 56% of patients received 4 mg of dexamethasone for the first 5 days of each cycle. Biochemical response rates, PSA decline and progression-free survival (PFS) were analyzed after one, three, and five cycles of RLT. Results: PSA response rates were not significantly different between patients receiving 177Lu-PSMA-617 plus dexamethasone and those receiving 177Lu-PSMA-617 alone after one, three, and five cycles (33% vs 39%, P =.62; 45% vs 45%, P = 1.0; and 38% vs 42%, P =.81). However, there was a nonsignificant trend for a more pronounced PSA decline in patients with bone metastases receiving adjunct dexamethasone (−21% ± 50% vs +11% ± 90%, P =.08; −21% ± 69% vs +22% ± 116%, P =.07; −13% ± 76% vs +32% ± 119%, P =.07). Median PFS tended to be longer in patients with bone metastases receiving 177Lu-PSMA-617 plus dexamethasone (146 vs 81 days; hazard ratio: 0.87 [95% confidence interval: 0.47-1.61]; P =.20). Multiple regression analysis showed that age (P =.0110), alkaline phosphatase levels (P =.0380) and adjunct dexamethasone (P =.0285) were independent predictors of changes in PSA in patients with bone metastases. Conclusions: We observed high response rates to 177Lu-PSMA-617 RLT in men with mCRPC. The short-term addition of dexamethasone to 177Lu-PSMA-617 had no striking antitumor effect but might enhance biochemical responses in patients with bone metastases. Future trials are warranted to test this hypothesis in a prospective setting.