Background: Pseudocarcinomatous hyperplasia (PCH) and marked tissue neutrophilia have been observed in cutaneous CD30+ anaplastic large cell lymphoma (ALCL) occasionally and may cause misdiagnosis. Methods: An unusual case of CD30+ ALCL of the skin resembling keratoacanthoma (KA) both clinically and pathologically was described. Histologic examination and immunostaining were performed. Results: A 55-year-old woman presented with a 3-month history of an enlarging hyperkeratotic tumor on the forehead with a central keratinous plug. Microscopic examination showed epithelial hyperplasia resembling KA and a diffuse background infiltrate of large atypical lymphoid cells in the dermis. The atypical cells resembled epithelial cells and were obscured by a massive infiltrate of eosinophils and neutrophils. Immunostaining confirmed the presence of a diffuse infiltrate of CD30+ cells; these cells were negative for CD45RO, CD20, CD15, epithelial membrane antigen, anaplastic lymphoma kinase-1, and cytokeratin. There was no evidence of extracutaneous involvement. The findings were consistent with primary cutaneous CD30+ ALCL of null cell phenotype with KA-like epithelial hyperplasia and marked eosinophilia and neutrophilia. Conclusions: Our case illustrates that primary cutaneous ALCL may be associated with KA-like PCH and concurrent marked tissue eosinophilia and neutrophilia. Diagnosis in such cases is challenging both clinically and histologically because the large atypical lymphoid cells may easily be obscured by the massive infiltrates of eosinophils and neutrophils or confused with invasive squamous cell carcinoma.
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