Canonical Wnt signaling pathway (WSP) alterations in metastatic prostate cancer.
Authors: Choi Sharon , Pan Elizabeth , Elliott Andrew , Beltran Himisha , Panian Justine , Jamieson Christina , Bagrodia Aditya , Rose Brent S. , Herchenhorn Daniel , Heath Elisabeth I. , Nabhan Chadi , Antonarakis Emmanuel S. , McKay Rana R. 
Published: January 2024

221 Background: WSP aberrations have been implicated in the progression and treatment resistance of metastatic prostate cancer (mPCa). Sustained exposure of PCa to androgen deprivation has been shown to regulate the canonical WSP, induce beta-catenin expression and stabilization, and promote androgen independence. This study interrogates a large dataset to characterize the molecular and immune landscape of canonical WSP-altered mPCa and associations with survival outcomes. Methods: We examined PCa patients who underwent tissue-based DNA and RNA sequencing through a CLIA-certified commercial assay (Caris Life Sciences). Comprehensive genomic profiling included next-generation sequencing (NGS) of DNA (592-gene panel or whole exome) and RNA (whole transcriptome), on tissue samples from primary prostatic and/or metastatic sites. Tumor samples were categorized as having aberrant canonical Wnt signaling (WSP-act) if they harbored activating mutations in CTNNB, pathogenic RSPO2 fusions, or inactivating mutations in either APC or RNF43. Subset analysis was conducted in mPCa samples with microsatellite stability (MSS), after excluding those with RNF43 (p.G659fs*) mutations which are passenger events in MSI-high cancers. Statistical significance was determined using Fisher's Exact or X2 tests with Benjamini–Hochberg correction. Overall survival (OS) data was obtained from insurance claims and was analyzed using Kaplan-Meier estimation. Results: Of all PCa samples (4,150) (N = 4,150), 17.4% (n = 722) were classified as WSP-act; 299 (41.4%) were from the primary tumor and 423 (58.6%) were from metastatic sites. WSP-act tumors were more prevalent in brain (46%), liver (31%), lung (31%) and bone (25%) metastases compared to primary prostate cancers (10%). The MSS mPCa subgroup (N=1,638) comprised 321 WSP-act and 1,317 WSP-WT tumors. WSP-act mPCa exhibited more SPOP mutations (14.2% vs. 6.3%, p < 0.001) as well as higher mRNA expression of CST1, NKD1, and ODAM (known canonical WSP activators) compared to WSP-WT cases. M2 macrophages predominated the tumor microenvironment, with a higher median fraction in WSP-act tumors compared to WSP-WT (7.2 vs. 6.1%, p < 0.001). ROR1 gene expression was significantly elevated in WSP-act tumors from both primary and metastatic sites. There was no significant difference in OS outcomes between WSP-act and WSP-WT mPCa patients. Conclusions: WSP-act prostate cancer demonstrated a pronounced upregulation of ROR1 gene expression, underscoring its potential involvement in the crosstalk between the canonical and non-canonical Wnt signaling pathways. Additionally, the augmented levels of M2 macrophages in WSP-act tumors, combined with the reported role of ROR1 in tumor immunosuppression, suggests that ROR1 may contribute to immune evasion in WSP-act mPCa. Our findings may provide rationale for developing novel therapeutic strategies targeting Wnt-activated prostate cancers.