Radioligand therapy using [¹⁷⁷Lu]Lu-PSMA-617 in mCRPC: a pre-VISION single-center analysis

Radioligand therapy with [¹⁷⁷Lu]Lu-PSMA-617 is efficacious for the treatment of patients with metastasized castration-resistant prostate cancer (mCRPC). Various studies have evaluated the efficacy and safety of [¹⁷⁷Lu]Lu-PSMA-617 using a dose of 6.0 GBq and an 8-week therapy interval. However, the first prospective phase III trial (VISION) plans to use an elevated cumulative dose by applying 7.5 GBq in a 6-week interval. The aim of the present study was to compare safety and efficacy of the two aforementioned [¹⁷⁷Lu]Lu-PSMA-617 therapy regimes (7.5 GBq every 6 weeks vs. 6.0 GBq every 8 weeks).

A total number of 78 consecutive patients with mCRPC and a history of first-line chemotherapy were included in this retrospective analysis. The outcome of patients treated with 6.0 GBq [¹⁷⁷Lu]Lu-PSMA-617 per cycle (n = 37) were compared with those treated with 7.5 GBq (n = 41) per cycle. The median therapy intervals were 8.4 weeks (6.0 GBq group) vs. 6.5 (7.5 GBq group). PSA response, PSA progression-free survival (PSA-PFS), overall survival, and adverse events were evaluated and compared between both groups. Chi-squared test, Kaplan Meier estimates, Cox regression, and log-rank test were used. The highest decline from pretherapeutic PSA levels was measured as percentage (best PSA response) and compared between groups by Wilcoxon test.

There was no significant difference comparing the rate of > 50% PSA decline or best PSA response between the 6.0 GBq and 7.5 GBq group (35% vs. 54%, p = 0.065; and - 40.2% vs. - 57.8%, p = 0.329). The median estimated survival and PSA-PFS did not significantly differ between the 6.0 GBq and 7.5 GBq groups as well (11.3 vs. 12.7 months, p = 0.384; and 9.5 vs. 12.3 months, p = 0.258). There was no significant difference regarding the change of kidney, liver, and blood cell parameters under therapy between the treatment groups.

Higher cumulated doses of [¹⁷⁷Lu]Lu-PSMA-617 were well tolerated and caused no significantly increased rate of adverse reactions. Moreover, 7.5 GBq of [¹⁷⁷Lu]Lu-PSMA-617 every 6 weeks causes slightly higher, though not statistically significant, response rates and seems therefore to be the preferable treatment regime. However, future studies are needed to elucidate the dose-related efficacy of [¹⁷⁷Lu]Lu-PSMA-617 as a way to personalized medicine.