Importantly, the phenotypes of skin cancer and psoriasis in Pla2g2a−/− mice were absent when both genotypes were co-housed in the same cages (which resulted in mixing of the microbiota through coprophagia) or when these mice were housed in a more stringent pathogen-free facility, in which the expression of Pla2g2a in WT mice was reduced and the composition of gut microbiota in the two genotypes became largely even if not solely identical. This evidence concerns the gene PLA2G2A and skin neoplasm.