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.