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Pagetoid reticulosis (PR) is a low-grade primary cutaneous T-cell lymphoma that usually presents as a solitary, slowly enlarging erythematous or hyperkeratotic plaque on the distal areas of the extremities. Histopathologically, it is characterized by a dense, band-like infiltrate of atypical lymphocytes with prominent epidermotropism within a hyperplastic epidermis, and immunophenotypic studies show in most cases, a CD4-positive T-helper phenotype for the neoplastic lymphocytes. We describe an African man with a more than 20-year history of an acral lesion of PR, which was histopathologically characterized by lymphocyte immunophenotype consisting of CD8- and CD30-positive cells. We discuss the differential diagnosis with other primary cutaneous lymphoproliferative disorders showing similar immunophenotype. This case shows that CD30-positive PR should be included as a rare variant within the spectrum of CD30-positive primary cutaneous lymphoproliferative disorders. As in other primary cutaneous CD30-positive lymphoproliferative processes, lesions of CD30-positive PR show an indolent course and a benign biological behavior.

Mutations in beta-catenin are present in benign pilomatrixomas. beta-catenin is a downstream effector in the WNT-signalling pathway, acting as a signal for differentiation and proliferation. Mutations in CTNNB1, the gene encoding beta-catenin, are present in a wide variety of benign and malignant neoplasms. We examined beta-catenin in a series of pilomatrix carcinomas (15 cases) by using immunohistochemistry and DNA sequencing of exon 3 from CTNNB1, and compared these to a series of benign pilomatrixomas (13 cases). All 11 pilomatrix carcinomas available for examination showed nuclear localization of beta-catenin and mutations in exon 3 similar to those demonstrated in benign pilomatrixomas. Two of 11 pilomatrix carcinomas showed significant nuclear accumulation of p53, whereas this was absent in all 13 benign pilomatrixomas. Expression of nuclear cyclin D1 was similar in both benign pilomatrixomas and pilomatrix carcinomas. Clinical follow-up from the 15 malignant cases reported in this study and by others indicates that wide excision offers superior control of local recurrence, compared to simple excision. Immunohistochemical and molecular analysis of beta-catenin reveals that both pilomatrix carcinomas and benign pilomatrixomas harbour mutations in beta-catenin. This implies a common initial pathogenesis and is compatible with the proposition that pilomatrix carcinomas may at least on occasion arise from their benign counterparts.