Expression of p16 in Merkel cell carcinoma

Merkel cell carcinoma: updates in tumor biology, emerging therapies, and preclinical models

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine carcinoma thought to arise via either viral (Merkel cell polyomavirus) or ultraviolet-associated pathways. Surgery and radiotherapy have historically been mainstays of management, and immunotherapy has improved outcomes for advanced disease. However, there remains a lack of effective therapy for those patients who fail to respond to these established approaches, underscoring a critical need to better understand MCC biology for more effective prognosis and treatment. Here, we review the fundamental aspects of MCC biology and the recent advances which have had profound impact on management. The first genetically-engineered mouse models for MCC tumorigenesis provide opportunities to understand the potential MCC cell of origin and may prove useful for preclinical investigation of novel therapeutics. The MCC cell of origin debate has also been advanced by recent observations of MCC arising in association with a clonally related hair follicle tumor or squamous cell carcinoma in situ. These studies also suggested a role for epigenetics in the origin of MCC, highlighting a potential utility for this therapeutic avenue in MCC. These and other therapeutic targets form the basis for a wealth of ongoing clinical trials to improve MCC management. Here, we review these recent advances in the context of the existing literature and implications for future investigations.

Feline papillomavirus-associated Merkel cell carcinoma: a comparative review with human Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare skin tumor that shares a similar immunophenotype with Merkel cells, although its origin is debatable. More than 80% of human MCC cases are associated with Merkel cell polyomavirus infections and viral gene integration. Recent studies have shown that the clinical and pathological characteristics of feline MCC are comparable to those of human MCC, including its occurrence in aged individuals, aggressive behavior, histopathological findings, and the expression of Merkel cell markers. More than 90% of feline MCC are positive for the Felis catus papillomavirus type 2 (FcaPV2) gene. Molecular changes involved in papillomavirus-associated tumorigenesis, such as increased p16 and decreased retinoblastoma (Rb) and p53 protein levels, were observed in FcaPV2-positive MCC, but not in FcaPV2-negative MCC cases. These features were also confirmed in FcaPV2-positive and -negative MCC cell lines. The expression of papillomavirus E6 and E7 genes, responsible for p53 degradation and Rb inhibition, respectively, was detected in tumor cells by in situ hybridization. Whole genome sequencing revealed the integration of FcaPV2 DNA into the host feline genome. MCC cases often develop concurrent skin lesions, such as viral plaque and squamous cell carcinoma, which are also associated with papillomavirus infection. These findings suggest that FcaPV2 infection and integration of viral genes are involved in the development of MCC in cats. This review provides an overview of the comparative pathology of feline and human MCC caused by different viruses and discusses their cell of origin.

Merkel cell carcinoma: an update

Merkel cell carcinoma (MCC) is an uncommon primary cutaneous neuroendocrine carcinoma associated with an adverse prognosis. In recent years, our understanding of MCC biology has markedly progressed. Since the discovery of the Merkel cell polyomavirus, it has become clear that MCC represents an ontogenetically dichotomous group of neoplasms with overlapping histopathology. Specifically, most MCCs arise secondary to viral oncogenesis, while a smaller subset is the direct result of UV-associated mutations. The distinction of these groups bears relevance in their immunohistochemical and molecular characterization, as well as in disease prognosis. Further recent developments relate to the landmark utilization of immunotherapeutics in MCC, providing optimistic options for the management of this aggressive disease. In this review, we discuss both fundamental and emerging concepts in MCC, with a particular focus on topics of practical relevance to the surgical or dermatopathologist.

Comparison of Prognostic Factors for Merkel Cell Carcinoma, Mucosal Melanoma and Cutaneous Malignant Melanoma: Insights into Their Etiologies

Little is known about the epidemiology of Merkel cell carcinoma (MCC) and mucosal melanoma (MM). Using the United States (US) National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) program data, we compared MCC and MM with cutaneous malignant melanoma (CMM) with respect to incidence rates and prognostic factors to better understand disease etiologies. We describe the proportional incidences of the three cancers along with their survival rates based on 20 years of national data. The incidence rates in 2000–2019 were 203.7 per 1,000,000 people for CMM, 5.9 per 1,000,000 people for MCC and 0.1 per 1,000,000 people for MM. The rates of these cancers increased over time, with the rate of MM tripling between 2000–2009 and 2010–2019. The incidences of these cancers increased with age and rates were highest among non-Hispanic Whites. Fewer MCCs and MMS were diagnosed at the local stage compared with CMM. The cases in the 22 SEER registries in California were not proportional to the 2020 population census but instead were higher than expected for CMM and MCC and lower than expected for MM. Conversely, MM rates were higher than expected in Texas and New York. These analyses highlight similarities in the incidence rates of CMM and MCC—and differences between them and MM rates—by state. Understanding more about MCC and MM is important because of their higher potential for late diagnosis and metastasis, which lead to poor survival.

Large Cell Neuroendocrine Carcinoma of the Skin/Conjunctiva: A Series of 6 Cases including 1 Combined Case With Squamous Cell Carcinoma

ABSTRACT

This study sought to reveal the clinicopathologic characteristics of large cell neuroendocrine carcinoma (LCNEC) of the skin/conjunctiva. The retrieved patients included 3 men and 3 women with a median age of 85 (63-95) years. All lesions occurred on the face, including the ears, with a median tumor size of 11.5 (7-65) mm. Lymph node metastasis was observed in 5 (83%) of 6 cases, and distant metastasis was noted in 2 (33%). One patient (17%) who had a 13-mm-sized tumor died of the tumor 13 months after excision. All tumors were mainly located in the dermis, and one of them also exhibited intraepithelial spreading. The cytology resembled that of an LCNEC in other organs. No adnexal differentiation was observed. Five cases were of the pure type, but one had a component of squamous cell carcinoma. Immunoreactivities for CAM5.2, CK7, CK19, BerEP4, epithelial membrane antigen, neuron-specific enolase, synaptophysin, c-KIT, GATA3, and bcl-2 were frequently present, but CK20, neurofilament, Merkel cell polyomavirus large T antigen, mammaglobin, estrogen receptor, HER2, and TTF1 were completely negative in all cases. Mutant-pattern immunostaining of p53, PTEN, and Rb was frequently observed. The Ki67 rate exceeded 70% in all cases. LCNEC of the skin/conjunctiva is a morphologically-defined group of primary cutaneous/conjunctival neuroendocrine neoplasm, although it may be heterogeneous similar to other-site LCNEC or Merkel cell carcinoma. This study highlighted the predominant location for the face, high metastatic and lethal potential, possible combination with other tumor components, and frequent mutant-type immunoexpressions of p53, PTEN, and Rb in this tumor group.