Atypical cells in radiation dermatitis express factor XIIIa

Dendritic cells that express factor XIIIa are present in the normal dermis and are increased in a variety of pathologic conditions. Atypical dermal cells are often seen in biopsy specimens of skin that has been previously irradiated. We sought to determine whether the atypical dermal cells in chronic radiation dermatitis express factor XIIIa. We employed standard immunohistochemical techniques with antibodies to factor XIIIa and CD34 to study 16 biopsy samples showing changes of radiation dermatitis. All cases showed diffuse positive cytoplasmic staining of atypical dermal cells with antibody to factor XIIIa. Of 16 cases, 10 showed focal staining of dermal cells with antibody to CD34, but this antibody did not react with most of the atypical dermal cells. We conclude that the majority of atypical dermal cells in radiation dermatitis are derived from dermal dendritic cells which express factor XIIIa.