Tp53 Mutations In Circulating Tumor Dna In Men With Metastastic Castration-Resistant Prostate Cancer Mcrpc.

249Background: Genes involved in mCRPC, including the tumor suppressor gene TP53, can be monitored with ctDNA but implications are unclear. Methods: Between 8/6/15 to 9/19/18, patients with mCRPC with available ctDNA genomic data using Guardant360 (Guardant360, Redwood City, CA) were included. Relationships between various lines of therapy and TP53 mutational status were analyzed. Patients positive for TP53 mutants were categorized using mutant allelic fraction of u003e 0%, ≥0.5%, ≥1% and ≥5%. Results: This study included 215 patients with mCRPC, median age 70 (41-90), and 80% Caucasians who had ctDNA after one line treatment for CRPC that included abiraterone (55%), enzalutamide (22%), and sipuleucel T (21%). Frequent co-alterations with TP53 mutants after 1 line of CRPC therapy included AR (14%), NF1 (5%), EGFR (4%), and PIK3CA (4%). See Table for relationships between lines of therapy and mutant TP53 allelic fraction. Conclusions: In this cohort of men with mCRPC, a higher mutational burden of TP53 in ctDN...