Intraepidermal Merkel cell carcinoma: A case series of a rare entity with clinical follow up.

BACKGROUND: Merkel cell carcinoma (MCC) is a rare but aggressive cutaneous carcinoma. MCC typically involves dermis and although epidermotropism has been reported, MCC strictly intraepidermal or in situ (MCCIS) is exceedingly rare. Most of the cases of MCCIS described so far have other associated lesions, such as squamous or basal cell carcinoma, actinic keratosis and so on. Herein, we describe 3 patients with MCC strictly in situ, without a dermal component. METHODS: Our patients were elderly. 2 of the lesions involved the head and neck area and 1 was on a finger. All tumors were strictly intraepidermal in the diagnostic biopsies, and had histomorphologic features and an immunohistochemical profile supporting the diagnosis of MCC. Excisional biopsies were performed in 2 cases and failed to reveal dermal involvement by MCC or other associated malignancies. RESULTS AND CONCLUSION: Our findings raise the awareness that MCC strictly in situ does exist and it should be included in the differential diagnosis of Paget's or extramammary Paget's disease, pagetoid squamous cell carcinoma, melanoma and other neoplasms that typically show histologically pagetoid extension of neoplastic cells. Considering the limited number of cases reported to date, the diagnosis of isolated MCCIS should not warrant a change in management from the typical MCC.

Aberrant expression of FLI-1 in melanoma.

Friend leukemia integration site 1 (FLI-1) nuclear transcription factor has been proposed as a suitable tool in the differential diagnosis of small round cell sarcomas. It has also been described as a nuclear marker of endothelial differentiation. Expression of FLI-1 has been demonstrated in Ewing's sarcoma/primitive neuroectodermal tumor (ES/PNET) and vascular neoplasms. In the present study, we describe 2 cases of metastatic melanoma with small round blue cell morphology that showed strong nuclear expression of FLI-1. Because of the small round blue cell morphology and negative immunohistochemical staining for pan-melanocytic cocktail (HMB45, anti MART1 and anti-tyrosinase) and SOX10 in both cases, FLI-1 immunostaining was requested as part of the tumors workup. Ultimately, both cases were established as being metastatic melanoma. Dermatopathologists should be aware that melanoma can be strongly positive for FLI-1 and not misinterpret these cases for ES/PNET or vascular lesions, especially when melanomas show unusual morphology.