Pseudocarcinomatous hyperplasia mimicking squamous cell carcinoma in a case of CD56-positive cytotoxic T-cell lymphoma.

We present the case of an 84-year-old patient with a cutaneous CD56 positive cytotoxic T-cell lymphoma associated with substantial pseudocarcinomatous hyperplasia mimicking squamous cell carcinoma (SCC). The patient presented with a 7-month history of several progressive, ulcerated plaques on his right forearm. An initial biopsy showed changes consistent with a diagnosis of SCC for which the patient underwent surgical treatment. Several months later, the patient developed recurrent ulcerated plaques on the right forearm of which several biopsies were performed. The biopsies repeatedly showed marked pseudocarcinomatous hyperplasia resembling SCC. Deeper punch biopsies, however, showed a dense superficial and deep infiltrate of markedly atypical lymphocytes. Immunohistochemical analysis revealed strong positive staining for CD3, CD8, CD56 with negative stains for CD30 and Epstein-Barr virus-encoded small non-polyadenylated RNAs (EBER). Staining for beta F1 and gamma-delta T-cell receptor (γδ TCR) were both negative. This constellation was most consistent with a diagnosis of cutaneous peripheral T-cell lymphoma, unspecified in association with marked pseudocarcinomatous hyperplasia. Our case adds cutaneous peripheral T-cell lymphoma, unspecified to the list of conditions associated with pseudocarcinomatous hyperplasia (PCH) and illustrates once again the potential pitfalls of distinguishing marked pseudocarcinomatous hyperplasia from SCC.