Baseline and post-treatment circulating tumor cell (CTC) counts with prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy (TRT) in men with metastatic castration-resistant prostate cancer (mCRPC).

Abstract

158 Background: CTC counts are an independent prognostic factor in men with mCRPC; certain changes following treatment (conversion from detectable to undetectable or unfavorable to favorable) are associated with improved overall survival. Most PSMA-TRT efficacy data have focused on PSA or imaging changes. Here, we describe baseline and post-treatment CTC counts from subjects receiving PSMA-TRT. Methods: Men with mCRPC treated on prospective clinical trials of PSMA-TRT and with available CTC counts (CellSearch) were included in our analysis. Depending upon the era of the trial, post-treatment counts were performed at 4-6 (initial era) or 12 weeks (recent era) after a single cycle of PSMA-TRT (individual trial data reported elsewhere). We describe CTC counts at baseline and compare pre-treatment counts to those after PSMA-TRT. Results: 116 men treated with PSMA-TRT had baseline CTC count (90 with both pre- and post-treatment CTC). Forty-four patients (37.9%) received 177Lu-J951, 46 (39.7%) received 177Lu-PSMA-617, and 26 (22.4%) received 225Ac-J591. Median age was 71.5. Fifty-eight patients (50%) had previously received taxane chemotherapy, median PSA was 82.98 ng/mL, and 66 (56.9%) were in the high-risk Halabi (CALGB) prognostic group. Eighty-nine out of one hundred sixteen (76.7%) had detectable baseline CTC and 58/116 (50%) had unfavorable baseline CTC count. Forty-nine out of seventy (70%) had post-treatment CTC count decline, 23/70 (32.9%) converted from detectable to undetectable, and 17/47 (36.2%) converted from unfavorable to favorable. CTC changes stratified by type of PSMA-TRT are reported in the table. Conclusions: This is the largest analysis of CTC changes in patients who have received PSMA-TRT. In addition to PSA changes and other previously reported outcomes, even when low doses of radionuclide therapy as part of dose-escalation studies are included, the majority with detectable CTC counts have post-treatment CTC count decline. A significant portion of patients experience favorable CTC changes. [Table: see text]