177Lu-PSMA-I&T Demonstrates PSA Responses and a Manageable Toxicity Profile

Derya Tilki, MD

Radioligand therapy with 177Lu-PSMA-I&T elicited a 30% or greater prostate-specific antigen (PSA) response in more than half of patients with metastatic castration-resistant prostate cancer (mCRPC), according to data presented during the 2023 American Urological Association Annual Meeting in Chicago, Illinois.¹

“PSMA-targeted radioligand therapy with lutetium PSMA-617 is associated with prolonged overall survival in patients with metastatic castration-resistant prostate cancer, but data regarding the oncological efficacy and toxicity of lutetium PSMA-I&T are limited,” explained study author Derya Tilki, MD, visiting faculty at Koç University in Istanbul, Turkey, and urologist at Martini-Klinik Prostate Cancer Center, University Hospital Hamburg-Eppendorf, Germany.

Overall, 33 patients with mCRPC received a total of 88 cycles (median, 2 cycles; range, 1-7 cycles), of 177Lu-PSMA-I&T.

“177Lu-PSMA-I&T was given with a median activity of 7.5 GBq [IQR, 6.7 – 8.1] per cycle,” wrote study authors in their abstract.

Oncological outcomes measured included clinical progression-free survival (PFS), time interval from the first radioligand therapy cycle to any radiological or biological progression.

“We assessed response according to PSA changes and imaging response,” Tilki said.

The investigators utilized Common Toxicity Criteria for Adverse Events (CTCAE) to assess toxicity.

Median patient age at the time of first radioligand therapy cycle was 71.6 ± 10.7 years. PSA response of any amount was seen in 22 patients (69%), at least 30% in 18 patients (56%), at least 50% in 11 patients (33%), and at least 90% in 6 patients (33%).

Clinical PFS following the first cycle of radioligand therapy was 6.3 months, and overall survival following the first cycle was 21.4 months.

Regarding toxicities, nephrotoxicity was observed in 4 cases, with CTCAE grade of I to II in 2 patients, II to III in 1 patient, and III to IV in 1 patient. Hematotoxicity was experienced in 6 patients (18.2%). The investigators also reported 6 cases of grade I/II myelotoxicity (18.2%) and grade III/IV myelotoxicity in 3 cases (9.1%).

Limitations of the study included its retrospective nature as well as the varying histories of the patients included in the study, according to Tilki.

“These are one of the few data for PSMA radioligand therapy with PSMA I&T in contrast with PSMA-617, and the toxicity profile is very similar [to that of] PSMA-617,” Tilki said in her presentation of the data.

Reference

Demirkol MO, Esen B, Sen M, et al. Radioligand therapy with 177Lu-PSMA-I&T in patients with metastatic castration-resistant prostate cancer: oncological outcomes and toxicity profile. Presented at: American Urological Association Annual Meeting, April 28-May 1, Chicago, Illinois. Abstract MP11-07