Although we observed a consistent loss of alpha diversity in patients and mouse models of PCa, we did not find a conserved set of taxa systematically altered in PCa samples, except for a significant increase in Firmicutes in fecal samples from early metastatic PCa (High PSA BCR) and in the Pten−/−; Rb1−/− mouse tumours. This evidence concerns the gene KLK3 and posterior cortical atrophy.