ATOH1 and Merkel cell skin cancer: Additionally, mutations in several genes, including the tumour suppressor ATOH1, encoding a transcription factor involved in Merkel cell differentiation, and PIK3CA, which codes for phosphatidylinositol 4,5-bisphosphate 3-kinase, catalytic subunit, alpha isoform, have been found in subsets of MCC [10, 14].