Characterization of Wnt signaling pathway (WSP) aberrations in advanced prostate cancer.

203 Background: Aberrations in Wnt signaling pathway (WSP) are implicated in disease progression and resistance of multiple malignancies including prostate cancer (PCa). We sought to characterize the clinical phenotype and molecular genotype of PCa patients with WSP alterations. Methods: Eligible patients included those with PCa having undergone clinical-grade next generation DNA sequencing of tumor derived from prostate or metastasis tissue. We identified patients with somatic activating mutations in CTNNB1 and RSPO2, or inactivating mutations in APC, RNF43, or ZNRF3. Patient and disease characteristics were collected. Clinical and outcome parameters were associated with WSP mutation status using STATA(V. 13.1, College Station, Texas). Results: A total of 169 patients were identified of whom 29 (18.1%) had a WSP activating mutation. Median age of the overall cohort was 64.85 (IQR 56.77, 70.36). 115 (68.0%) patients had Gleason 8-10 disease, 34 (20.1%) presented with de novo metastatic disease, 85 (50.3%) developed CRPC and 23 (13.6%) developed visceral metastases. Clinical characteristics were similar between biomarker groups. There was no association with the presence of a Wnt activating mutation and RB1, p53, pTEN, or BRCA1/2 alteration. Median time to CRPC was 39.42 (IQR 14.50 – 87.52) and 24.39 (IQR 14.99 – 46.03) months for no-WSP and WSP-aberrant respectively. Median 5-year OS was 83.7% (95% CI 73.0-90.4%) and 79.6% (95% CI 52.9 – 92.2%) months for no-WSP and WSP-aberrant respectively. Table evaluates biomarker status with time to CRPC development and overall survival (OS). Conclusions: We observe that somatic WSP activating mutations are present in 18.1% of patients with mPCa, consist with prior reports. Understanding the clinical significance of WSP alterations is critical to inform treatment strategies in patients with advanced disease.[Table: see text]