226Background: Sarcomatoid carcinoma of the prostate is a rare variant of prostatic cancer and has a significantly worse prognosis. The genomic features underpinning this rare subtype of malignancy are not well understood, and at present, there are no effective therapies. Methods: Tissue from 1417 prostate cancer patients was assayed by hybrid-capture based comprehensive genomic profiling (CGP) in the course of clinical care to evaluate genomic alterations (GA: base substitutions, indels, amplifications, copy number alterations, fusions/rearrangements) and targeted therapy opportunities. Tumor mutational burden (TMB) was calculated from a minimum of 1.11 Mb sequenced DNA and reported as mutations/Mb. Results: Profiling identified different patterns in GAs between prostate adenocarcinoma (1409) and prostate sarcomatoid carcinoma (8) (table), most notably in the commonly identified alterations in prostate cancers: TP53, RB1, and TMPRSS2-ERG. Additionally, the PI3K/mTOR pathway was altered in 50% of the sarc...