Bazyar, Soha

PURPOSE Randomized clinical trials (RCTs) have shown progression-free survival (PFS) benefits of metastasis-directed therapy (MDT) without androgen deprivation therapy for oligometastatic castration-sensitive prostate cancer (omCSPC). Most patients with bone metastatic (BM) omCSPC recur with additional bone disease after MDT. We hypothesized the BM-targeting alpha-emitter radium-223 dichloride (Ra223) could target subclinical bone disease and delay progression. METHODS This is an investigator-initiated, multicenter, open-label phase II RCT. Eligible men with recurrent omCSPC with ≥one bone metastasis (≤three on conventional imaging and/or ≤five on molecular imaging) were randomly assigned (1:1) to stereotactic ablative radiation (SABR) MDT alone or SABR MDT with Ra223 (six cycles). Primary end point was composite PFS. RESULTS From August 9, 2019, to March 2, 2023, 64 patients were randomly assigned, 33 to SABR MDT and 31 to SABR MDT/Ra223 balancing for key covariates. Most SABR MDT/Ra223 patients (87%) received six cycles of Ra223. The median PFS was 11.8 months with SABR MDT and 10.5 months with SABR MDT/Ra223 (adjusted hazard ratio [aHR], 1.42 [95% CI, 0.79 to 2.56]; P = .24). Seven patients (11%) experienced grade 3 treatment-related adverse events (no grade 4 or 5), 2 of 33 (6%) with SABR and 5 of 30 (17%) with SABR MDT/Ra223. Patients with high-risk (HiRi) pathogenic mutations in ATM , BRCA1/2 , RB1 , or TP53 had worse PFS (HR, 5.95 [95% CI, 1.83 to 19.3]; P = .003). Greater T-cell receptor (TCR) unique productive rearrangements were prognostic for improved PFS independent of the treatment arm (aHR, 0.45 [95% CI, 0.21 to 0.96]; P = .04). CONCLUSION Adding Ra223 to SABR MDT in BM omCSPC does not delay progression of disease. We provide evidence for an HiRi mutational signature and TCR repertoire as prognostic biomarkers in omCSPC treated with SABR MDT, highlighting the importance of collecting biological correlates in RCTs for omCSPC.

Abstract Background: The trajectory of metastatic castration-sensitive prostate cancer varies based on disease presentation and biology. While proteomic profiling studies of primary prostate tissue have linked protein expression with metastatic progression and prognosis, few studies have explored biological changes after treatment and their associations with response. Therefore, we conducted proteomic profiling of patients with oligometastatic castration-sensitive prostate cancer (omCSPC) treated with stereotactic ablative radiotherapy (SABR) or observation in the ORIOLE phase 2 randomized clinical trial (RCT). Methods Plasma from omCSPC patients in the ORIOLE trial was collected at baseline (day 1), day 90, and day 180. Protein abundance was quantified using the Olink Explore Assay. Differential expression from baseline to day 90 or 180 in each treatment arm was analyzed using a 2-sided t-test with Benjamini-Hochberg correction. Changes in protein expression at day 90 and 180 were compared with a Pearson correlation. Pathway enrichment was performed via gene set enrichment analysis (GSEA) using Reactome, KEGG, and Hallmark gene sets. Associations with progression-free survival (PFS) were analyzed using Kaplan-Meier and log-rank tests. Results In total, 1,472 proteins were assayed across 130 samples from 46 patients over 3 time points. Significant changes in expression post-SABR were noted at day 90 and 180 compared to baseline (using adjusted p-value cutoff of 0.05). At day 90, four proteins (FCRL1, CD22, TCL1A, FCER2) were downregulated; at day 180, only FCRL1, a Fc receptor-like gene family preferentially expressed in B cells, remained downregulated. No significant expression changes were found in the observation arm. Differential expression of proteins during follow-up were associated with PFS. In particular, LTO1, a maturation factor of ABCE1 important for ribosomal biogenesis and translation, was overexpressed at both day 90 and 180 post-SABR, and overexpression was associated with improved PFS at day 90 (median 24.5 mo vs 6 mo; p=0.017) and day 180 (median 33 mo vs 6 mo; p=0.043). These associations were absent in the observation arm. For proteins differentially expressed in the SABR arm at day 90, several signaling pathways were significantly enriched for patients with prolonged PFS, including positive enrichment of unfolded protein response (UPR) (p=0.008) and IL-4/IL-13 (p=0.009). At 180 days, several pathways were enriched for patients with prolonged PFS including negative enrichment of CTLA4 inhibitory signaling (p=0.005) and CD28 co-stimulation (p=0.008). Conclusion Proteomic analysis in omCSPC patients from the ORIOLE trial reveals significant expression changes at days 90 and 180 after SABR. B-cell signaling proteins were selectively downregulated in the SABR arm, and pathways associated with protein translation and immune response were enriched post-SABR for patients with prolonged PFS. Further research will explore connections to genomic and transcriptomic changes, with additional validation needed. Citation Format: Jarey H. Wang, Amol Shetty, Yang Song, Noura Radwan, Soha Bazyar, Xiaolei Shi, Theodore L. DeWeese, Daniel Y. Song, Ryan M. Phillips, Matthew P. Deek, Philip Sutera, Ana P. Kiess, Phuoc T. Tran. Proteomic profiling of oligometastatic castration-sensitive prostate cancer treated with stereotactic ablative radiotherapy. [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Targeted Therapies in Combination with Radiotherapy; 2025 Jan 26-29; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(2_Suppl):Abstract nr B031.

199 Background: Contained within the spectrum of metastatic cancer is an oligometastatic state where metastases are limited in number. Recent prospective data have shown that metastasis directed therapy (MDT) can alter the natural history of oligometastatic disease. In hormone-sensitive prostate cancer (HSPC), the positive clinical effect of MDT has been observed by the phase II STOMP and ORIOLE trials. Circulating tumor cells (CTCs) are a likely origin of the formation of macroscopic metastases. CTCs thus may provide an approach for identifying subgroups of patients with oligometastatic HSPC (oligoHSPC) that would benefit most from MDT. Our main goal was to evaluate the association between presence of CTCs at baseline or day 180 with clinical outcomes in the ORIOLE trial. Methods: ORIOLE was a phase II trial randomizing men with recurrent oligoHSPC with 1-3 metastases to observation (Obs) versus stereotactic ablative radiotherapy (SABR) MDT. Blood samples were prospectively collected at baseline and day 180. Progression-free survival (PFS) was a composite endpoint including any of the following: a PSA rise of at least 2 ng/dL and 25% above nadir; radiologic progression by CT, MRI or bone scan (RECIST v1.1); symptomatic progression of disease; initiation of ADT; or death. Patient blood samples were shipped for analysis on Epic Sciences liquid biopsy platform (Epic Sciences, San Diego, CA). Machine learning algorithms identified CTCs and characterized androgen receptor (AR) expression. Comparisons of patient and tumor characteristics between the groups were performed by two-sample t-tests. Survival curves were generated using the Kaplan-Meier method and p-values were calculated using log-rank test. Analysis was performed using SPSS version 28. Results: A total of 82 samples were collected: 70 from the SABR arm (35 baseline and 35 on day 180) and 12 Obs (7 baseline and 5 on day 180). CTCs were detected in 30/42 samples at baseline (71%, AR+= 7) and in 26/40 samples on day 180 (65%, AR+= 9). In the SABR group there was no difference between CTC+ versus CTC- and AR + versus AR- groups for PSA evaluated at baseline, day 90 or day 180 or Gleason score. With a median follow-up of 41.7 months, PFS was significantly lower in the patients with AR+ versus AR- CTCs at baseline in the SABR arm (p = 0.011, mean PFS: AR+ = 9.3 months, AR- = 27.1 months). The mean biochemical failure-free survival was AR+= 12.9 versus AR-= 29.2 months (p = 0.058). Conclusions: Our preliminary results demonstrate an association between AR+ CTCs at baseline and Day 180 with clinical outcomes following SABR MDT in oligoHSPC. This is the first report examining baseline and dynamic presence of CTCs in oligoHSPC treated from a prospective randomized trial of SABR. Longer follow-up, further analysis and a greater number of patients are needed for a more comprehensive conclusion.