PDCD1 and Merkel cell skin cancer: Multiple LSD1 inhibitors inhibit MCC growth in vitro and in xenograft models.The hypomethylating agent decitabine inhibited virus-positive MCC cells in vitro and in xenograft models.Histone deacetylase inhibition combined with PD-1/PD-L1 blockade did not show clinical benefit in a series of four patients.