A combined occurrence of neuroendocrine carcinoma of the skin and a benign appendageal neoplasm

Evidence of proliferative activity in human Merkel cells: implications in the histogenesis of Merkel cell carcinoma

The cellular origin of Merkel cell carcinoma (MCC) is controversial. We previously hypothesized that MCC originates from hair follicle stem cells or Merkel cell (MC) progenitors residing within the hair follicle bulge. Examination of three cases of combined MCC led to the unexpected discovery that numerous keratin 20 (CK20)-positive MCs within the squamous cell carcinoma (SCC) component of combined MCC appeared morphologically normal with dendritic and oval shapes. Moreover, one extremely rare case of combined SCC and MCC showed both intra-epidermal and dermal MCCs. These three cases represent the first documentation of MC hyperplasia in MCC, besides various benign follicular neoplasms associated with MC hyperplasia. Therefore, to elucidate the proliferating potential of MCs and their histogenetic relationship with MCCs, we further investigated these cases based on pathological observations. We identified numerous cells co-expressing CK20 and the proliferation marker Ki-67, identical to the morphological and immunohistochemical features of normal MCs. This finding indicated that MCs can no longer be considered as pure post-mitotic cells. Instead, they have proliferative potential under specific conditions in the diseased or wounded skin, or adjacent to various skin tumors, including MCC. Intimate co-existence of two malignant cell components composed of intradermal and intra-epidermal MCCs, with the proliferation of normal-appearing MCs in the same lesion, lends support to the hypothesis that MCs and MCC cells are derived from MC progenitors residing within the hair follicle bulge. Specifically, MCCs are derived from transformed MC progenitors with potential for dual-directional differentiation towards neuroendocrine and epithelial lineages.

Cutaneous squamous and neuroendocrine carcinoma: genetically and immunohistochemically different from Merkel cell carcinoma

Cutaneous neuroendocrine (Merkel cell) carcinoma most often arises de novo in the background of a clonally integrated virus, the Merkel cell polyomavirus, and is notable for positive expression of retinoblastoma 1 (RB1) protein and low expression of p53 compared with the rare Merkel cell polyomavirus-negative Merkel cell carcinomas. Combined squamous and Merkel cell tumors are consistently negative for Merkel cell polyomavirus. Little is known about their immunophenotypic or molecular profile. Herein, we studied 10 combined cutaneous squamous cell and neuroendocrine carcinomas for immunohistochemical expression of p53, retinoblastoma 1 protein, neurofilament, p63, and cytokeratin 20 (CK20). We compared mutation profiles of five combined Merkel cell carcinomas and seven 'pure' Merkel cell carcinomas using targeted next-generation sequencing. Combined tumors were from the head, trunk, and leg of Caucasian males and one female aged 52-89. All cases were highly p53- and p63-positive and neurofilament-negative in the squamous component, whereas RB1-negative in both components. Eight out of 10 were p53-positive, 3/10 p63-positive, and 3/10 focally neurofilament-positive in the neuroendocrine component. Six out of 10 were CK20-positive in any part. By next-generation sequencing, combined tumors were highly mutated, with an average of 48 mutations per megabase compared with pure tumors, which showed 1.25 mutations per megabase. RB1 and p53 mutations were identified in all five combined tumors. Combined tumors represent an immunophenotypically and genetically distinct variant of primary cutaneous neuroendocrine carcinomas, notable for a highly mutated genetic profile, significant p53 expression and/or mutation, absent RB1 expression in the context of increased RB1 mutation, and minimal neurofilament expression.

New insights into merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare aggressive cutaneous malignancy of the elderly and immunocompromised populations. The clinical presentation of MCC is nonspecific, with the majority of cases presenting as localized skin involvement. Histologically and immunophenotypically, MCC is defined by both neuroendocrine and epithelial differentiation. Recently, the Merkel cell polyomavirus has been implicated in the pathogenesis of MCC. In addition, there have been numerous studies evaluating the histologic and immunohistochemical characteristics of MCC as they relate to diagnosis and prognosis. The purpose of this paper is to review the most salient and clinically relevant updates in the pathogenesis and histologic features of MCC. Specific attention is given to the clinical and histologic predictors of prognosis, staging, and the controversies concerning sentinel lymph node biopsy and therapy.

Merkel cell carcinoma within follicular cysts: report of two cases

Merkel cell carcinoma is a rare cutaneous neoplasm of unknown histogenesis. Several reports have described the association of Merkel cell carcinoma of the skin with other cutaneous neoplasms within the same lesion, and there are also reports describing three examples of Merkel cell carcinoma within follicular cysts. We describe two examples of Merkel cell carcinoma developed within epithelial cysts. Neoplastic cells of Merkel cell tumor expressed immunoreactivity for chromogranin, synaptophysin, neuron-specific enolase, CAM 5.2 and cytokeratin 20, the last two markers showing the characteristic paranuclear dot-like pattern. In contrast, the epithelial wall lining the cyst and surrounding Merkel cell tumor only expressed immunoreactivity for cytokeratin MNF116. The description of five cases of Merkel cell carcinoma within follicular cysts, including the two cases of this report, support some relationship between Merkel cell tumor and the hair follicle.

Primary neuroendocrine (Merkel cell) carcinoma of the skin: morphologic diversity and implications thereof

A significant proportion of primary neuroendocrine cell carcinomas of the skin (Merkel cell carcinomas [MCCs]) have been reported to occur in intimate association with malignant epithelial neoplasms, mainly squamous cell carcinomas. In addition, divergent differentiation within these tumors, particularly of squamous and eccrine types, is not infrequent. This expanded morphologic spectrum of MCC calls for evaluation of potential biologic implications of the phenotypic diversity and begs reconsideration of the histogenesis of the lesion. The current retrospective review of 29 cases of primary cutaneous neuroendocrine cell carcinoma aims to address these issues by integrating new information with that which is extant. Eleven tumors were associated with evolving or established cutaneous carcinomas: 2 actinic keratoses, 5 Bowen's disease, 3 superficial squamous cell carcinomas, and 1 basal cell carcinoma. Two combined squamous-neuroendocrine tumors occurred in recipients of solid organ transplants, and another developed in a Marjolin's ulcer at the site of a previous burn. Squamous and/or adnexal differentiation within the dermal component of the tumor was observed in 4 instances and was significantly associated with MCCs in intimate association with another cutaneous carcinoma. The outcome of the group as a whole is similar to that recorded in previous series of MCC, with local recurrence in 32% of cases and death caused by the neoplasm in 28%. Only 52% of the patients were alive with no history of metastasis at follow-up. No significant difference in outcome was observed between the patients with pure MCCs and those with MCCs in combination with another cutaneous carcinoma.

Merkel cell carcinoma of the skin

BACKGROUND

Neuroendocrine/Merkel cell carcinoma (MCC) of the skin is an uncommon tumour. Currently, there are only limited data available on the natural history, prognostic factors, and patient management of MCC.

OBJECTIVES

To review our experience and build the largest database from the literature.

METHODS

Twenty-eight cases from the London Regional Cancer Center were combined with 633 cases obtained from the literature searched in English, French, German, and Chinese for the years 1966 to 1998. The database included age, sex, initial disease status at presentation to the clinic, site of primary, any coexisting disease, any previous irradiation, sizes of primary/nodal/distant metastases, management details, and final disease status. A new modified staging system was used: stage Ia (primary disease only, size > 2 cm), stage Ib (primary disease only, size > 2 cm); stage II (regional nodal disease), and stage III (beyond regional nodes and/or distant disease).

RESULTS

Age > 65 years, male sex, size of primary > 2 cm, truncal site, nodal/distant disease at presentation, and duration of disease before presentation (< or =3 months) were poor prognostic factors. Surgery was the initial treatment of choice and it significantly improved overall survival (p =.004).

CONCLUSIONS

We identified poor prognostic factors that may necessitate more aggressive treatment. The suggested staging system, incorporating primary tumour size, accurately predicted outcomes.

Intraepidermal Merkel cell carcinoma with no dermal involvement

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.

Primary cutaneous neuroendocrine (Merkel cell) carcinoma in association with squamous- and basal-cell carcinoma

The co-existence of squamous-cell carcinoma (SCC) and neuroendocrine (Merkel cell) carcinoma (NEC) of the skin has been well documented in several patients. The concurrent development of NEC and basal-cell carcinoma (BCC) in the same cutaneous lesion, on the other hand, has not been reported. We describe a 68-year-old man presenting with NEC, SCC, and BCC arising at the same site in retroauricular skin. Cells of NEC and SCC showed an intermingled pattern of growth, whereas those of BCC were "embedded" among those of the other two tumors. Immunohistochemical stains were consistent with the histopathologic diagnosis. We believe that this is the first report of the association of NEC, SCC, and BCC in the same skin lesion.

Combined neuroendocrine carcinoma of the skin (Merkel cell tumor) and trichilemmal cyst

We report a case of neuroendocrine (Merkel cell) carcinoma (NC) of the skin, associated with a trichilemmal cyst, showing pagetoid spread into the trichilemmal epithelium. The association of the two lesions may strengthen the hypothesis that NC originates from pluripotent stem cells of adnexal epithelium.