Intraepidermal Merkel Cell Carcinoma With No Dermal Involvement

Abstract

Cutaneous Merkel cell carcinoma (MCC) typically involves the dermis. Less than 10% of MCC have epidermal involvement. Only one MCC confined exclusively to the epidermis has been previously reported but was not recognized until the lesion recurred with typical MCC in the dermis. We present a case of a wholly intraepidermal pagetoid MCC without dermal involvement in a 74-year-old man with a 2.0-cm solitary verrucous papule on the left index finger. The initial biopsy and complete excision specimens showed marked epidermal hyperplasia, focal prominent squamous cell atypia, and MCC with florid pagetoid spread through the epidermis. There was no evidence of tumor within the dermis. The pagetoid MCC tumor cells showed diffuse cytoplasmic staining with antibodies to cytokeratin 20, and negative staining for chromogranin, neurofilament, S-100, vimentin, HMB45, leukocyte common antigen, and CD3. The cell of origin of MCC is still debated. The existence of an entirely intraepidermal variant of MCC would lend support to the view that MCC is a neoplastic expression of Merkel cells in at least some cases. Dermal-based MCC is a high-grade primary cutaneous neoplasm, but MCC confined exclusively to the epidermis may have a better prognosis.

Immunohistochemical Distinction Between Merkel Cell Carcinoma and Small Cell Carcinoma of the Lung

“…6 In 1978, Tang and Toker 7 demonstrated ultrastructurally the presence of dense core granules in 3 cases of MCC. The histogenesis of this tumor from Merkel cells has been supported by the recently described intraepidermal development of MCC lacking a dermal component, [8][9][10] as well as by the detection of intraepidermal spread in various cases of MCC. 3 On immunohistochemical assessment, Merkel cells have been found to express a variety of neuroendocrine markers, including neurofilaments, 11,12 neuron specific enolase, 13 chromogranin A, 14 neural cell adhesion molecule (NCAM/CD56), 14,15 synaptophysin, 16,17 somatostatin, 17 bombesin, and vasoactive intestinal peptide.…”

Histologic Mimics of Basal Cell Carcinoma

“…However, unlike BCC, MCC may have an intraepidermal component. [108][109][110][111] Both MCC and BCC may have focal or extensive squamous differentiation. 105 Peripheral palisading may be identified in a few MCC tumors but is typically focal.…”

Merkel Cells, Normal and Neoplastic: An Update

“…The epidermis is rarely involved [2] (Figure 5), but there is a report of an exclusively intraepidermal MCC [24]. A variable lymphoid infiltrate is usually present in the tumor stroma [3].…”