Contrasting genomic profiles in post-systemic treatment metastatic sites (MET), pretreatment primary tumors (PT), and liquid biopsies (LB) of clinically advanced prostate cancer (PC).

Abstract

5534 Background: Comprehensive genomic profiling (CGP) was done on pre-systemic treatment (pre) PT, post-treatment (post) MET sites and LB in PC to uncover differences in genomic alterations (GA) and potential impact on therapy selection. Methods: 1,294 PC tissues and 782 LB underwent hybrid-capture based CGP. PT biopsies and resections were compared with post-treatment MET biopsies from bone (BO), liver (LIV), lung (LU), brain (BN), lymph node (LN) and soft tissue (ST) sites and LB. TMB was determined on up to 1.1 Mbp of sequenced DNA for tumor samples. Tumor cell PD-L1 IHC was measured (Dako 22C3). Results: Differences in alteration frequencies between PT, MET and LB for selected genes are shown in the Table. TMPRSS2:ERG fusion frequencies were similar between PT and MET (35% vs 33%) but varied between MET sites (27% in BO and ST to 40% in LN). GA in AR were lowest in pre PT (2%) and highest in MET (24% in LU to 50% in LIV). BN had the highest GA/tumor (8) and the most PTEN GA. BRCA2 GA frequency varied from 0% in BN to 15% in LI. Potential predictors of IO response included CDK12 GA (16% in LU) and MSI high status (29% in BN). High PD-L1 expression was found in only two cases (LN) and low PD-L1 expression was relatively uncommon. ERBB2 amplifications were increased in MET compared with PT. RB1 GA were increased in LIV cases. LB GA had a similar increase in AR and TP53 GA to MET and appeared to be a blend of MET site biopsies across alteration frequencies. Conclusions: CGP of PT, MET and LB in PC demonstrates differences most likely associated with exposure to systemic therapies. Differences identified in the MET GA landscape suggest that liquid biopsies may capture a broader range of therapeutic opportunities for PC patients. [Table: see text]