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

Abstract

Background

Merkel cell carcinoma (MCC) is a rare but aggressive cutaneous carcinoma. MCC involves typically 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 associated other lesions, such as squamous or basal cell carcinoma, actinic keratosis, etc. Herein, we describe three patients with MCC strictly in situ, without a dermal component.

Methods

Our patients were elderly, two of the lesions involved the head and neck area and one was on a finger. All tumors were strictly intraepidermal in the diagnostic biopsies, had histomorphologic features and an immunohistochemical profile supporting the diagnosis of MCC. Excisional biopsies were performed in two 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.

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