G266 displayed a microsatellite instability profile with a homozygous deletion of MSH2 and a loss of MSH6. PDXs G266, C901 and C1022 shared a mutation profile representative of those observed in prostate metastatic tumors such as TMPRSS2-ERG fusion, TMPRSS2, RB1, BRCA2, and KMT2D mutations. The gene discussed is ERG; the disease is metastatic neoplasm.