PERP and neoplasm: As mast cells have been reported to surround tumors in a variety of cancers, including SCCs [65]–[68], and because they have been shown to play a key role in promoting tumorigenesis through the secretion of factors that remodel the tumor microenvironment and stimulate angiogenesis [68]–[71], their presence in the UVB-treated Perp-deficient mouse skin suggests an additional mechanism through which Perp loss may stimulate tumorigenesis.