Merkel cell carcinoma update: the case for two tumours

Combined Merkel Cell Carcinoma and Squamous Cell Carcinoma: A Systematic Review

Combined Merkel cell carcinoma (MCC) and squamous cell carcinoma (SCC) have classically been regarded as more aggressive than conventional, pure, Merkel cell polyomavirus (MCPyV)-positive MCC. It is still unknown whether combined MCC and SCC are more aggressive than pure, MCPyV-negative MCC, and the origin of both the SCC and MCC elements of these combined tumors has not been elucidated. The main objective of this systematic review was to assess whether combined MCC and SCC tumors are associated with a worse prognosis than pure MCC; the secondary goals were the characterization of the clinical and histopathological features of these combined neoplasms. A total of 38 studies, including 152 patients, were selected for review. In total, 76% of the cases were MCPyV-negative, whereas 4% were MCPyV-positive. The most frequent histopathological pattern was that of an SCC in situ combined with a dermal MCC (36%), followed by both an in situ and invasive SCC combined with a dermal MCC (20%). Forty-seven percent of all cases fitted in the morphology of the so-called "collision tumors". Three combined MCC cases that would fit in the morphological category of collision tumors presented both squamous and neuroendocrine elements in their respective nodal metastases. The mean overall survival was 36 months, comparable to that of pure, MCPyV-negative MCC. This review found similarly aggressive behavior for combined MCC and SCC and pure, MCPyV-negative MCC. Preliminary data strongly suggest that all MCPyV-negative MCC tumors, whether combined or pure, are part of a common spectrum.

Moderne Diagnostik und Therapie des Merkelzellkarzinoms

Das Merkelzellkarzinom (MCC) ist ein seltener, aggressiver Hauttumor mit epithelialer und neuroendokriner Differenzierung, dessen Inzidenz in den letzten Jahrzehnten deutlich zugenommen hat. Risikofaktoren sind fortgeschrittenes Lebensalter, heller Hauttyp, UV‐Exposition und Immunsuppression. Pathogenetisch wird ein durch das Merkelzell‐Polyomavirus (MCPyV) hervorgerufener Typ von einem UV‐induzierten Typ mit hoher Tumormutationslast unterschieden.

Klinisch präsentiert sich das MCC als meist schmerzloser, schnell wachsender, rötlich‐violetter Tumor mit glänzender Oberfläche, der bevorzugt im Kopf‐Hals‐Bereich und an den distalen Extremitäten lokalisiert ist. Eine sichere Diagnose kann nur anhand histologischer und immunhistochemischer Merkmale gestellt werden. Bei Erstdiagnose weisen 20%–26% der Patienten lokoregionäre Metastasen und 8%–14% Fernmetastasen auf, weshalb eine Ausbreitungsdiagnostik unabdingbar ist. Bei fehlenden klinischen Hinweisen auf Metastasen wird eine Sentinel‐Lymphknotenbiopsie empfohlen.

Wesentliche Säulen der Therapie sind die Operation, die adjuvante oder palliative Strahlentherapie und in fortgeschrittenen inoperablen Stadien die medikamentöse Tumortherapie. Die Einführung von Immuncheckpoint‐Inhibitoren führte zu einem Paradigmenwechsel, da sich hiermit ein wesentlich langfristigeres Ansprechen und bessere Überlebensraten als mit Chemotherapie erreichen lassen. Zur Therapie des metastasierten MCC ist in Deutschland der PD‐L1‐Inhibitor Avelumab zugelassen, aber auch die PD‐1‐Antikörper Pembrolizumab und Nivolumab werden mit Erfolg eingesetzt. Adjuvante und neoadjuvante Therapiekonzepte, Immunkombinationstherapien und zielgerichtete Therapien als Monotherapie oder in Kombination mit Immuncheckpoint‐Inhibitoren befinden sich in klinischer Prüfung.

Modern diagnostics and treatment of Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare, aggressive skin cancer with epithelial and neuroendocrine differentiation, the incidence of which has increased substantially during the last decades. Risk factors include advanced age, fair skin type, UV exposure, and immunosuppression. Pathogenetically, a type caused by the Merkel cell polyomavirus is distinguished from a UV-induced type with a high tumor mutational burden. Clinically, MCC presents as a mostly painless, rapidly growing, reddish-violet tumor with a shiny surface, which is preferentially localized in the head-neck region and at the distal extremities. A reliable diagnosis can only be made based on histological and immunohistochemical features. At initial diagnosis, 20-26% of patients show locoregional metastases and 8-14% distant metastases, making staging examinations indispensable. If there is no clinical evidence of metastases, a sentinel lymph node biopsy is recommended. Essential columns of therapy are surgery, adjuvant or palliative radiotherapy and, in advanced inoperable stages, medicamentous tumor therapy. The introduction of immune checkpoint inhibitors has led to a paradigm shift, as they provide a considerably longer duration of response and better survival rates than chemotherapy. The PD-L1 inhibitor avelumab is approved for treatment of metastatic MCC in Germany, but the PD-1 antibodies pembrolizumab and nivolumab are also used with success. Adjuvant and neoadjuvant treatment concepts, immune combination therapies and targeted therapies as monotherapy or in combination with immune checkpoint inhibitors are in the clinical trial phase.

miRNAs driving diagnosis, prognosis and progression in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare, aggressive form of skin malignancy with a high recurrence commonly within two to three years of initial diagnosis. The incidence of MCC has nearly doubled in the past few decades. Options for diagnosing, assessing, and treating MCC are limited. MicroRNAs (miRNAs) are a class of small, non-coding RNA molecules that play an important role in controlling many different aspects of cell biology. Many miRNAs are aberrantly expressed in distinct types of cancer, with some serving as tumor suppressors and others as oncomiRs. Therefore, the future holds great promise for the utilization of miRNAs in enhancing diagnostic, prognostic, and therapeutic approaches for MCC. Accordingly, the goal of this article is to compile, summarize, and discuss the latest research on miRNAs in MCC, highlighting their potential clinical utility as diagnostic and prognostic biomarkers.

Current and preclinical treatment options for Merkel cell carcinoma

INTRODUCTION

Merkel cell carcinoma (MCC) is a rare, highly aggressive form of skin cancer with neuroendocrine features. The origin of this cancer is still unclear, but research in the last 15 years has demonstrated that MCC arises via two distinct etiologic pathways, i.e. virus and UV-induced. Considering the high mortality rate and the limited therapeutic options available, this review aims to highlight the significance of MCC research and the need for advancement in MCC treatment.

AREAS COVERED

With the advent of the immune checkpoint inhibitor therapies, we now have treatment options providing a survival benefit for patients with advanced MCC. However, the issue of primary and acquired resistance to these therapies remains a significant concern. Therefore, ongoing efforts seeking additional therapeutic targets and approaches for MCC therapy are a necessity. Through a comprehensive literature search, we provide an overview on recent preclinical and clinical studies with respect to MCC therapy.

EXPERT OPINION

Currently, the only evidence-based therapy for MCC is immune checkpoint blockade with anti-PD-1/PD-L1 for advanced patients. Neoadjuvant, adjuvant and combined immune checkpoint blockade are promising treatment options.

Role of Sentinel Lymph Node Biopsy for Skin Cancer Based on Clinical Studies

The sentinel lymph node is the first lymph node from the primary tumor. Sentinel lymph node biopsy (SLNB) is a surgical procedure that can detect occult nodal metastasis with relatively low morbidity. It may also have a therapeutic effect via regional disease control. The Multicenter Selective Lymphadenectomy-I (MSLT-I) trial revealed a prognostic benefit from SLNB in melanoma patients. However, it remains unclear whether there is a prognostic benefit from SLNB in patients with nonmelanoma skin cancer owing to a lack of randomized prospective studies. Nevertheless, SLNB provides important information about nodal status, which is one of the strongest factors to predict prognosis and may guide additional nodal treatment. Currently, SLNB is widely used in the management of not only patients with melanoma but also those with nonmelanoma skin cancer. However, the utilization and outcomes of SLNB differ among skin cancers. In addition, SLNB is not recommended for routine use in all patients with skin cancer. In this review, we provide a summary of the role of SLNB and of the indications for SLNB in each skin cancer based on previously published articles.

4-[(5-Methyl-1H-pyrazol-3-yl)amino]-2H-phenyl-1-phthalazinone Inhibits MCPyV T Antigen Expression in Merkel Cell Carcinoma Independent of Aurora Kinase A

Merkel cell carcinoma (MCC) is frequently caused by the Merkel cell polyomavirus (MCPyV), and MCPyV-positive tumor cells depend on expression of the virus-encoded T antigens (TA). Here, we identify 4-[(5-methyl-1H-pyrazol-3-yl)amino]-2H-phenyl-1-phthalazinone (PHT)-a reported inhibitor of Aurora kinase A-as a compound inhibiting growth of MCC cells by repressing noncoding control region (NCCR)-controlled TA transcription. Surprisingly, we find that TA repression is not caused by inhibition of Aurora kinase A. However, we demonstrate that β-catenin-a transcription factor repressed by active glycogen synthase kinase 3 (GSK3)-is activated by PHT, suggesting that PHT bears a hitherto unreported inhibitory activity against GSK3, a kinase known to function in promoting TA transcription. Indeed, applying an in vitro kinase assay, we demonstrate that PHT directly targets GSK3. Finally, we demonstrate that PHT exhibits in vivo antitumor activity in an MCC xenograft mouse model, suggesting a potential use in future therapeutic settings for MCC.

A review on the oncogenesis of Merkel cell carcinoma: Several subsets arise from different stages of differentiation of stem cell

Merkel cell carcinoma (MCC), a rare primary cutaneous neuroendocrine neoplasm, is extremely aggressive and has a higher mortality rate than melanoma. Based on Merkel cell polyomavirus (MCPyV) status and morphology, MCCs are often divided into several distinct subsets: pure MCPyV-positive, pure MCPyV-negative, and combined MCC. MCPyV-positive MCC develops by the clonal integration of viral DNA, whereas MCPyV-negative MCC is induced by frequent ultraviolet (UV)-mediated mutations, that are characterized by a high mutational burden, UV signature mutations, and many mutations in TP53 and retinoblastoma suppressor gene (RB1). Combined MCC consists of an intimate mix of MCC and other cutaneous tumor populations, and is usually MCPyV-negative, with rare exceptions. Based on the existing subsets of MCC, it is speculated that there are at least 4 stages in the natural history of stem cell differentiation: primitive pluripotent stem cells, divergent differentiated stem cells, unidirectional stem cells, and Merkel cells (or epidermal/adnexal cells). In the first stage, MCPyV may integrate into the genome of primitive pluripotent stem cells, driving oncogenesis in pure MCPyV-positive MCC. If MCPyV integration does not occur, the stem cells enter the second stage and acquire the ability to undergo multidirectional neuroendocrine and epidermal (or adnexal) differentiation. At this stage, accumulated UV-mediated mutations may drive the development of combined MCC. In the third stage, the stem cells differentiate into unidirectional neuroendocrine stem cells, UV-mediated mutations can induce carcinogenesis in pure MCPyV-negative MCC. Therefore, it has been speculated that several subsets of MCCs arise from different stages of differentiation of common stem cells.

Combined Merkel cell carcinoma and cutaneous squamous cell carcinoma with lymph node metastases: Report of two cases

Merkel cell carcinoma (MCC) is an infrequent, aggressive cutaneous neoplasm, that typically affects the photodamaged skin of elderly individuals, and immunosuppressed patients. Because a subset of MCC is closely related to UV radiation, MCC can develop concurrently with other tumors, most commonly, as a combined tumor with squamous cell carcinoma (SCC). These combined tumors appear to represent a distinct disease process from pure MCC, as they are mostly Merkel cell polyomavirus (MCPyV) negative, and show a more aggressive behavior. We present two additional cases of combined MCC and SCC with nodal metastases, one of which was MCPyV positive. Two different subtypes of MCC have been proposed based on their origin: a true neuroendocrine carcinoma, that is MCPyV positive and has a dermal origin, and a UV-related SCC with neuroendocrine differentiation. This theory could explain why MCC can develop concurrently with SCC, and why these combined cases are generally MCPyV negative. However, it fails to explain the minority of combined MCC and SCC tumors that are MCPyV positive. Because both our patients had a history of chronic UV exposure, we hypothesize that UV radiation probably played a major role in the pathogenesis of these tumors, while MCPyV integration probably acted as an additional trigger.

Merkel Cell Polyomavirus: Infection, Genome, Transcripts and Its Role in Development of Merkel Cell Carcinoma

The best characterized polyomavirus family member, i.e., simian virus 40 (SV40), can cause different tumors in hamsters and can transform murine and human cells in vitro. Hence, the SV40 contamination of millions of polio vaccine doses administered from 1955-1963 raised fears that this may cause increased tumor incidence in the vaccinated population. This is, however, not the case. Indeed, up to now, the only polyomavirus family member known to be the most important cause of a specific human tumor entity is Merkel cell polyomavirus (MCPyV) in Merkel cell carcinoma (MCC). MCC is a highly deadly form of skin cancer for which the cellular origin is still uncertain, and which appears as two clinically very similar but molecularly highly different variants. While approximately 80% of cases are found to be associated with MCPyV the remaining MCCs carry a high mutational load. Here, we present an overview of the multitude of molecular functions described for the MCPyV encoded oncoproteins and non-coding RNAs, present the available MCC mouse models and discuss the increasing evidence that both, virus-negative and -positive MCC constitute epithelial tumors.

Merkel cell polyomavirus and associated Merkel cell carcinoma

Merkel cell polyomavirus (MCPyV) is a ubiquitous skin infection that can cause Merkel cell carcinoma (MCC), a highly lethal form of skin cancer with a nearly 50% mortality rate. Since the discovery of MCPyV in 2008, great advances have been made to improve our understanding of how the viral encoded oncoproteins contribute to MCC oncogenesis. However, our knowledge of the MCPyV infectious life cycle and its oncogenic mechanisms are still incomplete. The incidence of MCC has tripled over the past two decades, but effective treatments are lacking. Only recently have there been major victories in combatting metastatic MCC with the application of PD-1 immune checkpoint blockade. Still, these immune-based therapies are not ideal for patients with a medical need to maintain systemic immune suppression. As such, a better understanding of MCPyV's oncogenic mechanisms is needed in order to develop more effective and targeted therapies against virus-associated MCC. In this review, we discuss current areas of interest for MCPyV and MCC research and the progress made in elucidating both the natural host of MCPyV infection and the cell of origin for MCC. We also highlight the remaining gaps in our knowledge on the transcriptional regulation of MCPyV, which may be key to understanding and targeting viral oncogenesis for developing future therapies.

DNA-methylation patterns imply a common cellular origin of virus- and UV-associated Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a neuroendocrine tumor either induced by integration of the Merkel cell polyomavirus into the cell genome or by accumulation of UV-light-associated mutations (VP-MCC and UV-MCC). Whether VP- and UV-MCC have the same or different cellular origins is unclear; with mesenchymal or epidermal origins discussed. DNA-methylation patterns have a proven utility in determining cellular origins of cancers. Therefore, we used this approach to uncover evidence regarding the cell of origin of classical VP- and UV-MCC cell lines, i.e., cell lines with a neuroendocrine growth pattern (n = 9 and n = 4, respectively). Surprisingly, we observed high global similarities in the DNA-methylation of UV- and VP-MCC cell lines. CpGs of lower methylation in VP-MCC cell lines were associated with neuroendocrine marker genes such as SOX2 and INSM1, or linked to binding sites of EZH2 and SUZ12 of the polycomb repressive complex 2, i.e., genes with an impact on carcinogenesis and differentiation of neuroendocrine cancers. Thus, the observed differences appear to be rooted in viral compared to mutation-driven carcinogenesis rather than distinct cells of origin. To test this hypothesis, we used principal component analysis, to compare DNA-methylation data from different epithelial and non-epithelial neuroendocrine cancers and established a scoring model for epithelial and neuroendocrine characteristics. Subsequently, we applied this scoring model to the DNA-methylation data of the VP- and UV-MCC cell lines, revealing that both clearly scored as epithelial cancers. In summary, our comprehensive analysis of DNA-methylation suggests a common epithelial origin of UV- and VP-MCC cell lines.

The texture of collagen in the microenvironments of Merkel cell carcinoma

ABSTRACT

Solid tumors typically contain high levels of fibrillar collagen. The increased stromal collagen deposition usually promotes cancer progression since biochemical and biophysical cues from tumor-associated collagen fibers stimulate neoplastic cells. Few studies have investigated the relationship between Merkel cell carcinoma (MCC) and the extracellular matrix (ECM), but there are no works evaluating collagen.This is an observational, analytical, retrospective study including 11 patients with MCC. Primary tumor-stained sections were evaluated by second harmonic generation microscopy and texture analysis.Peritumoral texture features (area fraction, mean gray value, entropy, and contrast) showed much lower values than normal skin (P < .0001) revealing extensively altered structure of peritumoral collagen fibers. These differences were not significant between tumors with unfavorable and favorable known prognostic factors.Profound changes in collagen fibers present in the stroma accompanying primary MCC may contribute to the aggressive behavior of this tumor. Our results indicate that whatever MCC histological subtype, size or anatomical location, MCC promotes the same type of ECM for its development. As an outlook, therapies using ECM macromolecules or fibroblasts (the architects of ECM remodeling) as target could be useful in the treatment of MCC.

Non-coding RNA dysregulation in skin cancers

Skin cancers are the most common cancers worldwide. They can be classified in melanoma and non-melanoma skin cancer (NMSC), the latter includes squamous cell carcinoma (SCC), basal cell carcinoma (BCC) and merkel cell carcinoma (MCC). In recent years, the crucial role of non-coding RNAs (ncRNAs) in skin cancer pathogenesis has become increasingly evident. NcRNAs are functional RNA molecules that lack any protein-coding activity. These ncRNAs are classified based on their length: small, medium-size, and long ncRNAs. Among the most studied ncRNAs there are microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNA (circRNAs). ncRNAs have the ability to regulate gene expression at transcriptional and post-transcriptional levels and are involved in skin cancer cell proliferation, angiogenesis, invasion, and metastasis. Many ncRNAs exhibit tissue- or cell-specific expression while others have been correlated to tumor staging, drug resistance, and prognosis. For these reasons, ncRNAs have both a diagnostic and prognostic significance in skin cancers. Our review summarizes the functional role of ncRNAs in skin cancers and their potential clinical application as biomarkers.

Merkel Cell Polyomavirus‒Negative Merkel Cell Carcinoma Originating from In Situ Squamous Cell Carcinoma: A Keratinocytic Tumor with Neuroendocrine Differentiation

Although virus-negative Merkel cell carcinoma (MCC) is characterized by a high frequency of UV-induced mutations, the expression of two viral oncoproteins is regarded as a key mechanism driving Merkel cell polyomavirus‒positive MCC. The cells in which these molecular events initiate MCC oncogenesis have yet not been identified for both MCC subsets. A considerable proportion of virus-negative MCC is found in association with squamous cell carcinoma (SCC), suggesting (i) coincidental collision, (ii) one providing a niche for the other, or (iii) one evolving from the other. Whole-exome sequencing of four combined tumors consisting of SCC in situ and Merkel cell polyomavirus‒negative MCC showed many mutations shared between SCC and MCC in all cases, indicating a common ancestry and thereby a keratinocytic origin of these MCCs. Moreover, analyses of the combined cases as well as of pure SCC and MCC suggest that RB1 inactivation in SCC facilitates MCC development and that epigenetic changes may contribute to the SCC/MCC transition.

Keratoacanthoma: Update on the Debate

ABSTRACT

Keratoacanthoma (KA) is a cutaneous tumor with a biphasic pattern of growth. A rapidly growing phase is usually followed by involution. KA occurs on sun-damaged skin. There are many listed causative associations, which include some therapeutic agents. Debate continues as to whether KA is a variant of squamous carcinoma (SCC) or a separate entity. Reporting of KA versus SCC is markedly inconsistent. Reasons for inconsistency include overlapping microscopic criteria, variants of KA with more aggressive features, and possibly medicolegal concerns. Genetic studies have shown some differences between the 2 entities. Activation of apoptotic pathways has been demonstrated in KA. Genetic studies have shown a possible role of human polyomavirus 6 in the pathogenesis of at least some KAs. Given that some cases of KA have components that behave as conventional SCCs, KA can be considered as a low-grade variant of SCC with some genetic differences.

Merkel cell carcinoma: A review

Merkel cell carcinoma has been a focus of active scientific investigation in recent years and new information on the topic has emerged. Although uncommon, this primary cutaneous neuroendocrine carcinoma, usually involving the head/neck of elderly individuals, has a poor prognosis. Within the past two decades, an increase in the incidence of the tumor and the discovery of its link to the Merkel cell polyomavirus have focused medical attention on the lesion. The resulting studies have improved our understanding of the biology of the neoplasm and contributed to clinical care. Specifically, two pathogenic subsets of the tumor have come to light, the majority due to Merkel cell polyomavirus and the minority caused by ultraviolet radiation-induced genetic damage. This dichotomy carries prognostic implications favoring the former subset. In addition, having capitalized on the known susceptibility of the tumor to immune influences, investigators have recently discovered its responsiveness to immune checkpoint inhibition. This revelation has constituted a therapeutic milestone at the clinical level. Herein we provide an overview of the topic, outline updates in the field and place an emphasis on dermatopathologic aspects of Merkel cell carcinoma.

The Role of Epithelial-to-Mesenchymal Transition in Cutaneous Squamous Cell Carcinoma : Epithelial-to-Mesenchymal Transition in Cutaneous SCC

OPINION STATEMENT

The capacity of cells to modify their phenotypes from epithelial to mesenchymal (epithelial-to-mesenchymal transition or EMT) and vice versa provides them with a dynamic plasticity essential for human life, from embryogenesis to wound healing. Current knowledge about carcinogenetic mechanisms leaves little doubts on the pivotal participation of these interchangeable processes in cancer development, and their influence has been quite clearly established in the progression of cutaneous squamous cell carcinoma. A complex and ordered interplay of signals induces the shift between both phenotypes, providing cells with the most suitable state at every moment to face the next step in tumor invasion and dissemination. Some stimulatory triggers have opposite effects according to the biological context and in many cases exert collateral functions. This scenario makes finding an ideal therapeutic target difficult but provides the opportunity to intervene simultaneously at many different levels with small actions such as targeting the tumor environment. In any case, advances in knowledge of the EMT mechanisms and their influence on carcinogenesis and drug resistance will greatly influence the therapeutic strategies for many human tumors, including cutaneous squamous cell carcinoma.