The molecular and pathway characterization of patients with metastatic castration resistant prostate cancer (mCRPC) refractory to therapy with abiraterone acetate or enzalutamide: Preliminary results from the SU2C/PCF/AACR West Coast Prostate Cancer Dream Team (WCDT).

Abstract

79 Background: Progressive metastatic castration resistant prostate cancer (mCRPC) has historically been challenging to biopsy and characterize on a molecular basis because of its bone tropism. Since mechanisms of resistance to androgen signaling inhibitors such as enzalutamide or abiraterone are not fully understood, both an unbiased and a targeted assessment of the molecular landscape of these patients is required. Methods: Patients (pts) with mCRPC undergo biopsy at one of five West Coast Prostate Cancer Dream Team (WCDT) clinical sites, using a uniform biopsy protocol, following central radiologic review. Tissue is both frozen, and formalin fixed/paraffin embedded (FFPE). Frozen tissue undergoes laser capture microdissection (LCM) for RNA seq, DNA seq, and array comparative genomic hybridization (aCGH). An RNA seq process was developed that allows using extremely small quantities of RNA (approximately 1 ng). FFPE tissue undergoes a CLIA-certified assessment of a 37-gene mutational panel, FISH for AR, and IHC for PTEN. Peripheral blood is collected for miRNA, immune responses, and CTC analysis including aCGH. Pathway assessment integrating clinical, RNA seq, DNA seq, aCGH data is undertaken using PARADIGM analysis. Results: Thirty six of 300 planned mCRPC pts have undergone a metastasis biopsy: 17 from bone, eight from liver, one from lung, and 10 from distant lymph nodes. Tumor is present in around 75% of the frozen specimens. To date, LCM has been undertaken in 11 samples, with RNA seq done in six, DNA whole exome seq in one, aCGH in four. FFPE tissue has been evaluated by mutational panel sequencing (n=9), FISH for AR (n=11), and IHC for PTEN (n=13). CTC have been isolated in 33 pts. aCGH has been successfully undertaken in paired CTC and biopsy specimens. Expression data from patients with full RNA sequencing have been analyzed by PARADIGM, with top disrupted pathways identified. Conclusions: Biopsies of mCRPC, including from bony sites, can be undertaken and used for molecular and pathway analysis. Sufficient tissue for unbiased and targeted assessment can be obtained. Linkage of results from these studies to the clinical characteristics of these patients will reveal important insights into mechanisms of resistance.