Shared clonality in distinctive lesions of lymphomatoid papulosis and mycosis fungoides occurring in the same patients suggests a common origin.

Lymphomatoid papulosis (LyP) lies within the spectrum of primary cutaneous CD30-positive lymphoproliferative disorders. Approximately 10% to 15% of patients with LyP develop other lymphomas, most commonly mycosis fungoides (MF), suggesting a biological relationship between these distinctive diseases. Here, we describe the clinical and histopathologic features of 11 patients who had both LyP and MF, including a total of 30 biopsy specimens (14 LyP and 16 MF). Clinically, LyP lesions were characterized by clustered papules undergoing spontaneous regression and were classified as type A (n = 11), type C (n = 2), or type D (n = 1). All cases of MF were characterized clinically by patch/plaque disease, were stage I or II at the time of diagnosis, and consisted of a CD4-predominant epidermotropic T-cell infiltrate. We used polymerase chain reaction-based methods to assess the TCR-ß chain (TCRB) and TCR-γ chain (TCRG) in both LyP and MF lesions of all patients. Monoclonal TCR gene rearrangements were detected in 13 LyP lesions from 10 of 11 patients and in 14 MF lesions from 10 of 11 patients. All 10 patients in whom their skin lesions carried monoclonal TCR gene rearrangements exhibited overlapping clones in both their LyP and MF lesions; additional non-overlapping clones were identified in 3 LyP lesions from 2 patients and 1 MF lesion from another patient. The demonstration of shared monoclonal T-cell receptor gene rearrangements in LyP and MF lesions in almost all patients suggests a common origin between these distinctive clinicopathological diseases.

Pigmented extramammary Paget disease of the thigh mimicking a melanocytic tumor: report of a case and review of the literature.

IMPORTANCE: Extramammary Paget disease (EMPD) is an uncommon tumor that presents in apocrine-rich skin as an irregular, pruritic plaque. Histopathologically, EMPD consists of an intraepidermal proliferation of atypical epithelioid cells. Rarely, the tumor cells contain intracytoplasmic melanin pigment, and the lesion clinically and histopathologically can mimic a melanocytic proliferation. OBSERVATIONS: A 51-year-old female with a history of breast carcinoma presented with a pigmented patch on her right thigh of 6 months duration. The clinical impression was an atypical melanocytic nevus. Histopathologic examination revealed an intraepidermal proliferation of epithelioid cells along the dermal-epidermal junction with pagetoid migration. The tumor cells exhibited increased cytoplasm containing conspicuous melanin pigment and enlarged oval-irregular nuclei. Immunohistochemical studies showed the tumor cells to be strongly and diffusely positive for cytokeratin 8/18, cytokeratin 7 and p63; focally and weakly positive for epithelial membrane antigen (EMA), but negative for cytokeratin 5/6, Cam5.2, carcinoembryonic antigen (CEA), human melanoma black 45 (HMB-45), tyrosinase and Sox-10, supporting the diagnosis of pigmented EMPD. The lesion was subsequently excised, and the patient is free of disease after 24 months. CONCLUSION: We present this unusual case of pigmented EMPD arising on the thigh to draw attention to the entity and to underscore the potentially misleading clinical, histopathologic and immunophenotypic features that mimic other cutaneous intraepidermal lesions.