Dermatomyositis‐like skin eruptions under hydroxyurea therapy conceal TP53‐mutated atypical keratinocytes: A histopathologic and molecular pathologic case series

Hydroxyurea is an antimetabolite that inhibits DNA synthesis and is used as a treatment option in chronic myeloproliferative disorders. Rarely, “dermatomyositis (DM)‐like” skin lesions are observed after long‐term therapy. In this case series, five skin biopsies of four patients were evaluated by histology, immunohistochemistry, and next‐generation sequencing of the TP53 gene locus. All biopsies showed focal basal pleomorphic keratinocytes and suprabasal aberrant p53 expression as well as sparse to severe vacuolar interface dermatitis. Histopathologically, “DM‐like” skin lesions can be clearly distinguished from DM by marked subepidermal fibrosis, vascular proliferation, and the absence of dermal mucin deposits. In 75% of the specimens multiple, partly inactivating and/or pathogenic point mutations of TP53 were found in low frequencies. “DM‐like” skin eruptions as a long‐term consequence of hydroxyurea therapy are possibly not chemotherapy‐associated benign toxic changes, but rather inflammatory reactions to complex keratinocyte alterations that clinically mimic the picture of DM. Synergistic mutagenic effects of hydroxyurea and sunlight might be responsible for this unique drug side effect and could provide a pathogenic link to the known increased risk of skin cancer in these patients.