Background: A comprehensive assessment of biopsies from metastatic prostate cancer (mPCa) patients (pts) may identify a molecular subset of pts susceptible for immune checkpoint (IC) blockade (ICB).Methods: 148 biopsies and germline DNA from 145 mPCa pts were whole genome sequenced (WGS) at an average of 114x and 38x. Tumour mutational (mut) burden (TMB) was defined as number of somatic single nucleotide variants and InDels per Mb of the genome, known mut signatures (Alexandrov, Nature 2013) extracted by non-negative least squares regression as well as recurrent mutations reported in mismatch repair (MMR) pts (Kim, Cell 2013). [...]