Integrated analysis of tissue genomic sequencing and high purity circulating tumor cell RNA sequencing for prostate cancer lineage states as a prognostic factor for survival and resistance to 177Lu-PSMA-617 in patients with metastatic castrate resist

5085 Background: Genomic mutations, including RB1 , PTEN , and HRR genes, associate with poor prognosis and treatment resistance in metastatic prostate cancer (mPC). mPC lineage states such as neuroendocrine prostate cancer (NEPC) also drive resistance and poor survival. Identifying the timing and association of genomic mutations with lineage states has been limited by the challenges of obtaining serial tumor biopsies. We report an integrated analysis of clinical next-generation sequencing (NGS) data, ctDNA, and mPC lineage state phenotypes with a novel high purity circulating tumor cell (CTC) RNA sequencing method. Methods: We collected 273 CTC samples from 117 patients with mPC in a prospective biomarker trial. 69 patients had clinical NGS from a recent tissue biopsy and 60 patients treated with PSMA LU . CTCs were purified via immunomagnetic capture on a microfluidic platform and analyzed via RNA-seq. We compared CTC lineage states, somatic mutation status and median overall survival (mOS). Results: Gene expression analysis of high CTC purity samples identified four CTC phenotypes: luminal A-like (LumA), luminal B-like (LumB), low proliferation (LP), and neuroendocrine (NE). Compared to patients with low CTC burden/purity (mOS NR), patients with LumA and LP phenotypes had similar survival ((LumA: mOS 13mo, p=ns, LP: mOS: 11.8mo, p=ns), while patients with LumB and NE phenotypes had shorter survival (LumB: mOS 6mo, HR 9.1[3.8-21.8], p<0.0001, NE: mOS 3.7mo, HR 11.8[2.4-57.2]), p=0.0019). mOS for patients with high-risk genomic mutations ( RB1, PTEN, TP53 ) and a LumA or LP lineage state was 12.7mo versus 4mo for patients with high-risk mutations and a LumB or NE lineage state (HR 3.59 [1.51-8.51], p=0.004). mOS was not reached for patients without high-risk mutations and a LumA or LP lineage state vs 8mo for patients without high-risk mutations but a LumB or NE lineage state (HR 19.7 [1.99-1.95], p<0.0001). Among patients treated with 177Lu-PSMA-617 in a prospective substudy (n=37), no patients had pretreatment CTC NE phenotype, but pre-treatment CTC LumB phenotype was associated with decreased rPFS (3.5mo vs 11.7mo, HR 4.8 [95% CI 1.4-16.1], p<0.005) and OS (7.6mo vs NR, HR 9.3 [95% CI 2.3-37.8], p<0.0005) compared to pretreatment LumA/LP/Low CTC burden phenotypes. Conclusions: Lineage states detected by high purity CTC RNAseq are prognostic for poor OS and decreased benefit from 177Lu-PSMA-617. The presence of high-risk genetic mutations including RB1 is prognostic for poor OS and combined evaluation of high-risk genetic mutation status with lineage state phenotype identifies patients with the worst clinical outcomes that would benefit from treatment intensification and early disease monitoring for these more aggressive subtypes of mCRPC.