The etiology and epidemiology of merkel cell carcinoma

A Case of Merkel Cell Carcinoma of Unknown Primary Origin Presenting With High Merkel Cell Polyomavirus DNA Levels in Swabs Obtained From the Normal Skin

Merkel cell carcinoma is a rare neuroendocrine tumor with high mortality. It is well known that clonal integration of the Merkel cell polyomavirus into the dermal precursor cells is a hypothesized pathway in Merkel cell carcinoma pathogenesis. Here, we demonstrate a case of Merkel cell carcinoma (primary origin unknown) presenting with high Merkel cell polyomavirus DNA levels in swabs obtained from normal skin.

Merkel cell polyomavirus protein ALTO modulates TBK1 activity to support persistent infection

While Merkel cell polyomavirus (MCPyV or MCV) is an abundant virus frequently shed from healthy skin, it is one of the most lethal tumor viruses in immunocompromised individuals, highlighting the crucial role of host immunity in controlling MCPyV oncogenic potential. Despite its prevalence, very little is known about how MCPyV interfaces with the host immune response to maintain asymptomatic persistent infection and how inadequate control of MCPyV infection triggers MCC tumorigenesis. In this study, we discovered that the MCPyV protein, known as the Alternative Large Tumor Open Reading Frame (ALTO), also referred to as middle T, effectively primes and activates the STING signaling pathway. It recruits Src kinase into the complex of STING downstream kinase TBK1 to trigger its autophosphorylation, which ultimately activates the subsequent antiviral immune response. Combining single-cell analysis with both loss- and gain-of-function studies of MCPyV infection, we demonstrated that the activity of ALTO leads to a decrease in MCPyV replication. Thus, we have identified ALTO as a crucial viral factor that modulates the STING-TBK1 pathway, creating a negative feedback loop that limits viral infection and maintains a delicate balance with the host immune system. Our study reveals a novel mechanism by which a tumorigenic virus-encoded protein can link Src function in cell proliferation to the activation of innate immune signaling, thereby controlling viral spread, and sustaining persistent infection. Our previous findings suggest that STING also functions as a tumor suppressor in MCPyV-driven oncogenesis. This research provides a foundation for investigating how disruptions in the finely tuned virus-host balance, maintained by STING, could alter the fate of MCPyV infection, potentially encouraging malignancy.

Critical involvement of circular RNAs in virus-associated cancers

Virus-related cancer is cancer where viral infection leads to the malignant transformation of the host's infected cells. Seven viruses (e.g., human papillomavirus (HPV), Epstein-Barr virus (EBV), Kaposi's sarcoma herpesvirus (KSHV), Hepatitis B virus (HBV), Hepatitis C virus (HCV), Human T-lymphotropic virus (HTLV), and Merkel cell polyomavirus (MCV)) that infect humans have been identified as an oncogene and have been associated with several human malignancies. Recently, growing attention has been attracted to exploring the pathogenesis of virus-related cancers. One of the most mysterious molecules involved in carcinogenesis and progression of virus-related cancers is circular RNAs (circRNA). These emerging non-coding RNAs (ncRNAs), due to the absence of 5' and 3' ends, have high stability than linear RNAs and are found in some species across the eukaryotic organisms. Compelling evidence has revealed that viruses also encode a repertoire of circRNAs, as well as dysregulation of these viral circRNAs play a critical role in the pathogenesis and progression of different types of virus-related cancers. Therefore, understanding the exact role and function of the virally encoded circRNAs with virus-associated cancers will open a new road for increasing our knowledge about the RNA world. Hence, in this review, we will focus on emerging roles of virus-encoded circRNAs in multiple cancers, including cervical cancer, gastric cancer, Merkel cell carcinoma, nasopharyngeal carcinoma, Kaposi cancer, and liver cancer.

Characterization of molecular mechanisms driving Merkel cell polyomavirus oncogene transcription and tumorigenic potential

Merkel cell polyomavirus (MCPyV) is associated with approximately 80% of cases of Merkel cell carcinoma (MCC), an aggressive type of skin cancer. The incidence of MCC has tripled over the past twenty years, but there are currently very few effective targeted treatments. A better understanding of the MCPyV life cycle and its oncogenic mechanisms is needed to unveil novel strategies for the prevention and treatment of MCC. MCPyV infection and oncogenesis are reliant on the expression of the early viral oncoproteins, which drive the viral life cycle and MCPyV+ MCC tumor cell growth. To date, the molecular mechanisms regulating the transcription of the MCPyV oncogenes remain largely uncharacterized. In this study, we investigated how MCPyV early transcription is regulated to support viral infection and MCC tumorigenesis. Our studies established the roles of multiple cellular factors in the control of MCPyV gene expression. Inhibitor screening experiments revealed that the histone acetyltransferases p300 and CBP positively regulate MCPyV transcription. Their regulation of viral gene expression occurs through coactivation of the transcription factor NF-κB, which binds to the viral genome to drive MCPyV oncogene expression in a manner that is tightly controlled through a negative feedback loop. Furthermore, we discovered that small molecule inhibitors specifically targeting p300/CBP histone acetyltransferase activity are effective at blocking MCPyV tumor antigen expression and MCPyV+ MCC cell proliferation. Together, our work establishes key cellular factors regulating MCPyV transcription, providing the basis for understanding the largely unknown mechanisms governing MCPyV transcription that defines its infectious host cell tropism, viral life cycle, and oncogenic potential. Our studies also identify a novel therapeutic strategy against MCPyV+ MCC through specific blockage of MCPyV oncogene expression and MCC tumor growth.

Characterization of the Impact of Merkel Cell Polyomavirus-Induced Interferon Signaling on Viral Infection

Merkel cell polyomavirus (MCPyV) has been associated with approximately 80% of Merkel cell carcinoma (MCC), an aggressive and increasingly incident skin cancer. The link between host innate immunity, viral load control, and carcinogenesis has been established but poorly characterized. We previously established the importance of the STING and NF-κB pathways in the host innate immune response to viral infection. In this study, we further discovered that MCPyV infection of human dermal fibroblasts (HDFs) induces the expression of type I and III interferons (IFNs), which in turn stimulate robust expression of IFN-stimulated genes (ISGs). Blocking type I IFN downstream signaling using an IFN-β antibody, JAK inhibitors, and CRISPR knockout of the receptor dramatically repressed MCPyV infection-induced ISG expression but did not significantly restore viral replication activities. These findings suggest that IFN-mediated induction of ISGs in response to MCPyV infection is not crucial to viral control. Instead, we found that type I IFN exerts a more direct effect on MCPyV infection postentry by repressing early viral transcription. We further demonstrated that growth factors normally upregulated in wounded or UV-irradiated human skin can significantly stimulate MCPyV gene expression and replication. Together, these data suggest that in healthy individuals, host antiviral responses, such as IFN production induced by viral activity, may restrict viral propagation to reduce MCPyV burden. Meanwhile, growth factors induced by skin abrasion or UV irradiation may stimulate infected dermal fibroblasts to promote MCPyV propagation. A delicate balance of these mutually antagonizing factors provides a mechanism to support persistent MCPyV infection. IMPORTANCE Merkel cell carcinoma is an aggressive skin cancer that is particularly lethal to immunocompromised individuals. Though rare, MCC incidence has increased significantly in recent years. There are no lasting and effective treatments for metastatic disease, highlighting the need for additional treatment and prevention strategies. By investigating how the host innate immune system interfaces with Merkel cell polyomavirus, the etiological agent of most of these cancers, our studies identified key factors necessary for viral control, as well as conditions that support viral propagation. These studies provide new insights for understanding how the virus balances the effects of the host immune defenses and of growth factor stimulation to achieve persistent infection. Since virus-positive MCC requires the expression of viral oncogenes to survive, our observation that type I IFN can repress viral oncogene transcription indicates that these cytokines could be explored as a viable therapeutic option for treating patients with virus-positive MCC.

Merkel cell carcinoma: a forty-year experience at the Peter MacCallum Cancer Centre

BACKGROUND

Merkel cell carcinoma (MCC) is a rare but highly aggressive neuroendocrine skin malignancy, with Australia having the highest reported incidence in the world. There is currently a lack of consensus regarding optimal management of this disease.

METHODS

This was a retrospective audit conducted by reviewing existing medical records of MCC patients presenting to the Peter MacCallum Cancer Centre (PMCC) between 1980 and 2018. The primary endpoint was locoregional recurrence. The secondary endpoints were distant recurrence, disease-free survival (DFS) and overall survival (OS).

RESULTS

A total of 533 patients were identified. Locoregional recurrence occurring at one, two and 5 years was 24, 31 and 32%, respectively. The estimated 5-year OS and DFS were 46% (95% Confidence Interval [CI] 41-51%) and 34% (95% CI 30-39%) respectively. Older age at diagnosis (hazard ratio [HR] per year = 1.07, 95% CI 1.06-1.07, p < 0.001), and larger primary tumour diameter (HR =1.16, 95% CI 1.03-1.31, p = 0.019) were associated with worse OS on multivariable analysis. Positive or negative histopathological margin status was not associated with OS or DFS differences in patients treated with post-operative radiotherapy.

CONCLUSIONS

In our study, about a third of patients developed locoregional recurrence, distal recurrence or both, and there appears to be no change over the last four decades. If treated with adjuvant radiotherapy, there is no difference in OS or DFS with positive surgical margins. Findings should influence future guidelines.

Merkel cell carcinoma of unknown primary: Clinical presentation and outcomes

BACKGROUND

Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous malignancy that usually occurs in the head/neck or extremities. However, there are reports of MCC developing in the lymph nodes or parotid gland without evidence of a primary cutaneous lesion.

METHODS

We reviewed 415 patients with biopsy-proven MCC. Patients with MCC of unknown primary (n = 37, 9%, MCCUP) made up the study cohort. The primary endpoints of the study were rate of recurrence, disease-free survival, and overall survival.

RESULTS

Patients with MCCUP presented with tumors in lymph nodes (n = 34) or parotid gland (n = 3). Nodal disease was most commonly detected in the inguinal/external iliac (n = 15) or axillary (n = 14) regions. The mean age at diagnosis was 70 years and 24% were female. Patients presented with distant metastases in 24.3% of cases. Patients with stage IIIA disease treated with regional lymph node dissection (RLND) had a lower risk of disease recurrence (hazard ratio 0.26, p = 0.046). Recurrence-free survival was 59.3% at 5 years. Disease-specific survival was 63.3% at 5 years.

CONCLUSION

Patients with MCCUP have a high risk of recurrence and mortality. The optimal treatment for MCCUP has yet to be elucidated, although therapeutic RLND appears beneficial for these patients.

Nationwide multidisciplinary consensus on the clinical management of Merkel cell carcinoma: a Delphi panel

Merkel cell carcinoma (MCC) is a rare and highly aggressive cutaneous neuroendocrine carcinoma. The MCC incidence rate has rapidly grown over the last years, with Italy showing the highest increase among European countries. This malignancy has been the focus of active scientific research over the last years, focusing mainly on pathogenesis, new therapeutic trials and diagnosis. A national expert board developed 28 consensus statements that delineated the evolution of disease management and highlighted the paradigm shift towards the use of immunological strategies, which were then presented to a national MCC specialists panel for review. Sixty-five panelists answered both rounds of the questionnaire. The statements were divided into five areas: a high level of agreement was reached in the area of guidelines and multidisciplinary management, even if in real life the multidisciplinary team was not always represented by all the specialists. In the diagnostic pathway area, imaging played a crucial role in diagnosis and initial staging, planning for surgery or radiation therapy, assessment of treatment response and surveillance of recurrence and metastases. Concerning diagnosis, the usefulness of Merkel cell polyomavirus is recognized, but the agreement and consensus regarding the need for cytokeratin evaluation appears greater. Regarding the areas of clinical management and follow-up, patients with MCC require customized treatment. There was a wide dispersion of results and the suggestion to increase awareness about the adjuvant radiation therapy. The panelists unanimously agreed that the information concerning avelumab provided by the JAVELIN Merkel 200 study is adequate and reliable and that the expanded access program data could have concrete clinical implications. An immunocompromised patient with advanced MCC can be treated with immunotherapy after multidisciplinary risk/benefit assessment, as evidenced by real-world analysis and highlighted in the guidelines. A very high consensus regarding the addition of radiotherapy to treat the ongoing focal progression of immunotherapy was observed. This paper emphasizes the importance of collaboration and communication among the interprofessional team members and encourages managing patients with MCC within dedicated multidisciplinary teams. New insights in the treatment of this challenging cancer needs the contribution of many and different experts.

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.

Rare Cutaneous Malignancies in Skin of Color

BACKGROUND

There is a scarcity of information regarding the clinical characteristics of rare cutaneous malignancies in skin of color that has yet to be comprehensively explored.

OBJECTIVE

To review and compile the racial differences in epidemiology, clinical presentation, histology, treatments, and outcomes of 3 rare skin cancers: dermatofibrosarcoma protuberans (DFSP), Merkel cell carcinoma (MCC), and sebaceous carcinoma (SC).

METHODS

Several searches with keywords denoting specific skin cancer type and race were conducted on PubMed to complete this narrative review.

RESULTS

We analyzed 50 sources that were relevant to the initial objective.

CONCLUSION

The literature demonstrates that there are nuances in DFSP, MCC, and SC unique to African Americans, Asians/Pacific Islanders, and Hispanics that may differ significantly from Caucasian counterparts. African Americans consistently suffer from the worst clinical outcomes in all 3 rare cutaneous malignancies reviewed. Greater physician awareness and knowledge of the discussed racial differences is the preliminary step to address these disparities.

NeuN, a DNA-binding neuron-specific protein expressed by Merkel cell carcinoma: analysis of 15 cases

Aim

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine carcinoma, with an increasing worldwide incidence. It presents as a painless red to purple nodule on sun-exposed skin. MCC is presumed to arise from resident cutaneous Merkel cells. The pathogenesis of MCC is likely multifactorial with immunosuppression, UV-induced skin damage, and Merkel cell polyomavirus contributing to the development. The diagnosis of MCC relies upon characteristic morphologic features and use of immunohistochemical stains. Histologically, the differential diagnosis of Merkel cell carcinoma includes the ‘small round cell’ tumor group, particularly metastatic small cell carcinoma and hematological malignancies. This study investigates the expression of NeuN antibody, which recognizes the protein NeuN, normally present in most neuronal cell types and neuronal tumors, in Merkel cell carcinomas.

Methods and results

Fifteen cases of Merkel cell carcinoma (7 men and 7 women; mean age 74 years) were retrieved from the institute database between the years 2011-2020. The immunohistochemical profile was investigated: CK20 (14/14), Neurofilament, (12/12), Synaptophysin (14/14); Chromogranin A (11/13), PAX5 (10/12), TDT (5/12), CK7 (1/14), TTF1 (0/14). Infection by Polyoma virus was detected in 11 of 14 patients. Most tumors showed middle/strong expression of NeuN. No cutaneous structures, or epidermal Merkel cells, showed expression of NeuN. The expression of NeuN was investigated in 17 primary small cell lung carcinomas: 2 cases were positive for Neu-N.

Conclusions

Awareness of the staining pattern of Neu-N could aid in diagnosis of Merkel cell carcinoma, avoiding misinterpretation and erroneous diagnosis with other tumors.

Merkel cell carcinoma presenting as a malignant pleural effusion post-COVID-19 hospitalization: A case report and literature review

Merkel cell carcinoma (MCC) is a rare, highly aggressive neuroendocrine carcinoma of the skin, associated with immunosuppression, UV light exposure, and the Merkel cell polyomavirus (MCPyV). Cases of metastatic MCC diagnosed in body fluid cytology are extremely rare; only five cases have been reported previously in the English literature. We present a case of a 65-year-old male with acute respiratory failure and an enlarged right pleural effusion. He had two hospitalizations for COVID-19 pneumonia 2 months prior, for which he received steroid treatment and tocilizumab. Emergent thoracentesis was done, with pleural fluid sent for cytologic evaluation. Both the Papanicolaou stained ThinPrep slide and cell block demonstrated clusters of predominantly small to medium sized blue round cells with hyperchromatic nuclei, scant cytoplasm and fine chromatin, in a background of rare mesothelial cells, macrophages and numerous lymphocytes. Tumor cells were positive for CD56, chromogranin, synaptophysin, SAT2B, MCPyV, and CK20 in perinuclear dot like pattern, while negative for TTF-1 and CD45 immunostains. Ki67 proliferative index was approximately 40%. The patient had a history of MCC of the right ulnar forearm 4 years before the current presentation, which was unknown to us at the time of cytologic evaluation. To the best of our knowledge, this is the sixth case of metastatic MCC diagnosed by fluid cytology and the first reported in a patient receiving immunosuppressive treatment for COVID-19. Further reporting of such cases may increase awareness, especially when prior history is not readily available, such as in our case.

Merkel cell carcinoma in situ: A systematic review of prognosis and management

BACKGROUND

Merkel cell carcinoma (MCC) is a rare primary cutaneous neuroendocrine tumour. While dermally invasive MCC is known to have a five-year survival of only 30-40%, the prognosis and management of MCC in situ (MCCis) is not widely reported.

OBJECTIVE

We present a systematic review to elucidate the prognosis and management of MCCis.

METHODS

We performed a systematic review, searching three databases to 01 June 2021. Case reports, cohort studies, clinical trials and literature reviews were considered for inclusion.

RESULTS

We identified 26 cases of MCCis published in the literature with a median age of 74 years and involving 19 males and 7 females. Most cases were on the face and neck (n = 17), followed by upper limb (n = 8) and lower limb (n = 1). Sentinel lymph node biopsy was performed in three patients, and all were negative. One subject underwent adjuvant radiotherapy. No MCCis-associated deaths were reported.

CONCLUSION

This review suggests that MCCis has an excellent prognosis with minimal, if any, risk of mortality and a very low risk of dermal invasion and recurrence when treated with wide local excision alone. Sentinel lymph node biopsy is unlikely to be useful for MCCis.

Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare neuroendocrine carcinoma. The cellular origin of MCC may include Merkel cell precursors. The incidence of MCC has increased significantly however trends may have been confounded by evolving diagnostic criteria. The two key aetiologies of MCC are ultraviolet radiation and Merkel cell polyoma virus (MCPyV). Both have unique mechanisms of carcinogenesis. MCC presents non-specifically as a rapidly growing, red-to-violet nodule on sun-exposed areas. Diagnostic accuracy has improved through immunohistochemical markers such as CK-20. Lymph nodes should be evaluated in MCC through examination and sentinel biopsy. USS, CT, MRI and CT-PET may be useful in staging. Management depends on tumour location, stage and comorbidities. MCPyV status may guide treatment strategy in the future. Treatment for the primary MCC is commonly wide local excision followed by radiotherapy, guided by anatomical constraints. There is uncertainty about surgical margins. Treatments for nodal disease have not been determined through trials. They include nodal dissection or radiotherapy for clinically or radiologically apparent disease, and adjuvant nodal irradiation for negative nodes, microscopic disease or following nodal dissection for definite disease. Patients with loco-regional advanced inoperable disease should be considered for combination therapy including chemotherapy, radiotherapy, surgery and immunotherapy. Systemic therapy for advanced disease includes immune checkpoint inhibitors targeting the PD-1/PD-L1 pathway. Avelumab can improve survival in metastatic MCC. Immunotherapy may result in longer disease control. Various other immunotherapeutic and molecular agents are undergoing trials. MCC continues to have a high mortality characterized by high recurrence and early metastases.

Multimodal Strategy in Localized Merkel Cell Carcinoma: Where Are We and Where Are We Heading?

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumor of the skin whose incidence is rising. Multimodal treatment is crucial in the non-metastatic, potentially curable setting. However, the optimal management of patients with non-metastatic MCC is still unclear. In addition, novel insights into tumor biology and newly developed treatments (e.g., immune checkpoint inhibitors) that dramatically improved outcomes in the advanced setting are being investigated in earlier stages with promising results. Nevertheless, the combination of new strategies with consolidated ones needs to be clarified. We reviewed available evidence supporting the current treatment recommendations of localized MCC with a focus on potentially ground-breaking future strategies. Advantages and disadvantages of the different treatment modalities, including surgery, radiotherapy, chemotherapy, and immunotherapy in the non-metastatic setting, are analyzed, as well as those of different treatment modalities (adjuvant as opposed to neoadjuvant). Lastly, we provide an outlook of remarkable ongoing studies and of promising agents and strategies in the treatment of patients with non-metastatic MCC.

"Present and future of immunotherapy in Neuroendocrine Tumors"

Immunotherapy, so promising in many neoplasms, still does not have a precise role in the treatment of neuroendocrine neoplasms (NENs). In this article, we provide an overview on the current knowledge about immunotherapy with immune checkpoint inhibitors (ICIs) applied to NENs, evaluating future perspectives in this setting of tumors.Evidence so far available for ICIs in gastroenteropancreatic (GEP)-NENs is definitively not as robust as for other tumors such as Small Cell Lung Cancer or Merkel Cell Carcinoma. In fact, with regard to the well-differentiated forms of NENs (NETs), the results obtained nowadays have been disappointing. However, the near future, might reserve interesting results for ICIs in GEP-NEN from a total of nine different ICI drugs, used throughout 19 randomised controlled trials. Such numbers highlight the growing attention gathering around NENs and ICIs, in response to the need of stronger evidences supporting such therapy.For the future, the most important aspect will be to study strategies that can make NETs more susceptible to response to ICI and, thus, enhance the effectiveness of these treatments. Therefore, the combination of conventional therapy, target therapy and immunotherapy deserve attention and warrant to be explored. A sequential chemotherapy, possibly inducing an increase in tumor mutational burden and tested before immunotherapy, could be a hypothesis deserving more consideration. A radiation treatment that increases tumor-infiltrating lymphocytes, could be another approach to explore before ICIs in NENs. Equally essential will be the identification of biomarkers useful for selecting patients potentially responsive to this type of treatment.

Identification of natural product modulators of Merkel cell carcinoma cell growth and survival

Merkel cell carcinoma (MCC) is a rare, but aggressive skin cancer the incidence of which has increased significantly in recent years. The majority of MCCs have incorporated Merkel cell polyomavirus (VP-MCC) while the remainder are virus-negative (VN-MCC). Although a variety of therapeutic options have shown promise in treating MCC, there remains a need for additional therapeutics as well as probes for better understanding MCC. A high-throughput screening campaign was used to assess the ability of > 25,000 synthetic and natural product compounds as well as > 20,000 natural product extracts to affect growth and survival of VN-MCC and VP-MCC cell lines. Sixteen active compounds were identified that have mechanisms of action reported in the literature along with a number of compounds with unknown mechanisms. Screening results with pure compounds suggest a range of potential targets for MCC including DNA damage, inhibition of DNA or protein synthesis, reactive oxygen species, and proteasome inhibition as well as NFκB inhibition while also suggesting the importance of zinc and/or copper binding. Many of the active compounds, particularly some of the natural products, have multiple reported targets suggesting that this strategy might be a particularly fruitful approach. Processing of several active natural product extracts resulted in the identification of additional MCC-active compounds. Based on these results, further investigations focused on natural products sources, particularly of fungal origin, are expected to yield further potentially useful modulators of MCC.

Tumor primary site as a prognostic factor for Merkel cell carcinoma disease-specific death

BACKGROUND

Merkel cell carcinoma (MCC) primary site has not been fully investigated as a potential prognostic factor.

OBJECTIVE

To determine the incidence by tumor primary site of death due to MCC.

METHODS

We undertook a retrospective analysis of the Survival, Epidemiology, and End Results database. MCC patients treated between 1973 and 2016 were grouped by tumor primary site and a competing risks analysis was performed to test the impact of primary site on disease-specific death. Cumulative incidence of Merkel cell carcinoma-specific mortality (CMMI) at 5 years was estimated for each primary site.

RESULTS

Of 9407 MCC patients identified, 6305 (67.0%) had localized disease, 2397 (25.5%) had regional metastasis, and 705 (7.5%) had distant metastasis. Tumor primary site was predictive of CMMI and varied by stage at diagnosis. Tumors involving the scalp/neck carried the highest CMMI among localized MCC (26.0%). Tumors involving the lip had the highest CMMI among MCC with regional metastasis (56.7%) and distant metastasis (82.1%).

LIMITATIONS

Tumor size data were missing for a large proportion of patients, precluding stratification by stage according to current American Joint Committee on Cancer guidelines.

CONCLUSIONS

Probability of MCC disease-specific death varies by primary site. The primary site of the tumor may be useful as a prognostic indicator for MCC.

Primary Merkel Cell Carcinoma: The Clinical Experience of Taipei Veterans General Hospital Revisited

BACKGROUND

Merkel cell carcinoma (MCC) is rare among Asians. To evaluate the presence and characteristics of MCC in Taiwan, we described the characteristics, treatment, and prognostic findings of MCC in our institution.

METHODS

We revisited and carried out a retrospective chart review of 16 consecutive patients with MCC treated from 1995 to 2018. Patient demographic data, tumor size, location, previous treatment, and follow-up data about presence of locoregional recurrence and metastasis were evaluated.

RESULTS

There were 14 male and 2 female patients (mean age = 75.1 years; range = 26-91 years). Clinical follow-up revealed local recurrences in 5 patients 1 to 4 months after surgical excision. Lymph node metastasis was observed in 3 patients. We reviewed previously published articles and analyzed the clinical findings, pathologic examinations, and treatments.

CONCLUSIONS

Surgical wide excision of the primary tumor remains the mainstay of treatment for patients with local/regional MCC. Additional management strategies, such as lymphadenectomy, radiotherapy, chemotherapy, and targeted therapy, depend on the presence or absence of clinically detectable lymph node disease. The prognosis for MCC is variable. Our findings highlight the importance of maintaining a high clinical suspicion for this malignancy in the appropriate clinical context to avoid delays in diagnosis and management.

Assessment of Age, Period, and Birth Cohort Effects and Trends in Merkel Cell Carcinoma Incidence in the United States

Importance

Merkel cell carcinoma is an aggressive, cutaneous, neuroendocrine cancer that is increasing in incidence. Understanding why the incidence of Merkel cell carcinoma is increasing through underlying factors, such as age effects, calendar period of diagnosis effects, and birth cohort effects, can help guide resource allocation and design of screening programs.

Objectives

To evaluate the associations of patient age, calendar period of diagnosis, and birth cohort with the increasing incidence of Merkel cell carcinoma and to provide new incidence projections to 2030.

Design, Setting, and Participants

A cross-sectional retrospective study with age-period-cohort analysis and incidence projection modeling using data from the Surveillance, Epidemiology, and End Results Program database of 9 registries from 1987 to 2016 was conducted among 3720 patients with Merkel cell carcinoma. Statistical analysis was conducted from October 20, 2019, to July 29, 2020.

Exposures

Age effects (ie, physiology), period of diagnosis effects (ie, changes in diagnostics and clinical awareness), and birth cohort effects (ie, environmental risk factors) over time were assessed.

Main Outcomes and Measures

Incidence rates of Merkel cell carcinoma.

Results

Among the 3720 patients in the study (2200 male patients [59.1%]; median age, 77 years [interquartile range, 68-84 years]), during the period from 2012 to 2016, the age-adjusted Merkel cell carcinoma incidence rate was 0.66 per 100 000 (95% CI, 0.62-0.70), which represented a 3.5-times (95% CI, 3.0-4.2) increase from 1987 to 1991. The incidence of Merkel cell carcinoma increased with patient age across calendar periods and birth cohorts; the highest incidence rate was observed for those aged 85 years or older, with an age-adjusted rate from 2012 to 2016 of 14.6 per 100 000 for men and 5.5 per 100 000 for women. Although the birth cohort effect has continued to increase over time, the calendar period of diagnosis effect has started to plateau. It is projected that there will be 3023 new cases of Merkel cell carcinoma in 2020 and 5130 new cases in 2030, increased from an estimated 1933 cases in 2010.

Conclusions and Relevance

The slowing down of the period effect (ie, changes in diagnostics and awareness) found in this longitudinal cohort study suggests that part of the initial increased incidence of Merkel cell carcinoma was associated with increased detection. However, the projected increase in incidence rate is likely associated with the aging population and increasing risk factor exposure in more recent birth cohorts.

Molecular Profiling of Merkel Cell Polyomavirus-Associated Merkel Cell Carcinoma and Cutaneous Melanoma

Merkel cell carcinoma (MCC) is a rare, high-grade, aggressive cutaneous neuroendocrine malignancy most commonly associated with sun-exposed areas of older individuals. A relatively newly identified human virus, the Merkel cell polyomavirus (MCPyV) has been implicated in the pathogenesis of MCC. Our study aimed to examine nine MCC cases and randomly selected 60 melanoma cases to identify MCPyV status and to elucidate genetic differences between virus-positive and -negative cases. Altogether, seven MCPyV-positive MCC samples and four melanoma samples were analyzed. In MCPyV-positive MCC RB1, TP53, FBXW7, CTNNB1, and HNF1A pathogenic variants were identified, while in virus-negative cases only benign variants were found. In MCPyV-positive melanoma cases, besides BRAF mutations the following genes were also affected: PIK3CA, STK11, CDKN2A, SMAD4, and APC. In contrast to studies found in the literature, a higher tumor burden was detected in virus-associated MCC compared to MCPyV-negative cases. No association was identified between virus infection and tumor burden in melanoma samples. We concluded that analyzing the key morphologic and immunohistological features of MCC is critical to avoid confusion with other cutaneous malignancies. Molecular genetic investigations such as next-generation sequencing (NGS) enable molecular stratification, which may have future clinical impact.

Merkel Cell Polyomavirus and Human Merkel Cell Carcinoma

Merkel cell polyomavirus (MCPyV) is the most recently discovered human oncogenic virus. MCPyV asymptomatically infects most of the human population. In the elderly and immunocompromised, however, it can cause a highly lethal form of human skin cancer called Merkel cell carcinoma (MCC). Distinct from the productive MCPyV infection that replicates the viral genome as episomes, MCC tumors contain replication-incompetent, integrated viral genomes. Mutant MCPyV tumor antigen genes expressed from the integrated viral genomes are essential for driving the oncogenic development of MCPyV-associated MCC. In this chapter, we summarize recent discoveries on MCPyV virology, mechanisms of MCPyV-mediated oncogenesis, and the current therapeutic strategies for MCPyV-associated MCCs.

The changing paradigm of managing Merkel cell carcinoma in Australia: An expert commentary

Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine tumor of the skin with an estimated disease-associated mortality of 15-33%. Australia has a higher incidence of MCC compared to the rest of the world, thought to be due to a higher ultraviolet index. The Australian MCC population is distinct from the MCC population of the Northern hemisphere, characterized by a predominantly viral negative etiology with high tumor mutational burden. The optimal management of MCC and the choice of treatment modality vary significantly across the world and even between institutions within Australia. Historically, the treatment for MCC has been resection followed by radiotherapy (RT), though definitive RT is an alternative treatment used commonly in Australia. The arrival of immune checkpoint inhibitors and the mounting evidence that MCC is a highly immunogenic disease is transforming the treatment landscape for MCC. Australia is playing a key role in the further development of treatment options for MCC with two upcoming Australian/New Zealand investigator-initiated clinical trials that will explore the interplay of RT and immunotherapy in the treatment of early and late stage MCC.

Immunologic Characteristics of Nonmelanoma Skin Cancers: Implications for Immunotherapy

In this review, we summarize the immunology of nonmelanoma skin cancers (NMSCs) and the clinical data with immunotherapy in this heterogeneous group of cancers that include basal cell carcinoma (BCC), cutaneous squamous cell carcinoma (CSCC), and Merkel cell carcinoma (MCC). NMSCs are exceedingly common, and their treatment consumes substantial health care resources. Annual global mortality from NMSCs is comparable to that from malignant melanoma. Although the majority of NMSCs are localized at diagnosis and are treated effectively with surgery, metastases (nodal and distant) can sometimes arise and require systemic therapy. Given the success of immunotherapy in treating cutaneous melanoma, there has been an increasing interest in studying the immunology of NMSCs. Immunocompromised patients have a substantially higher risk of developing NMSCs (particularly CSCC and MCC), suggesting a role of the immune system in the pathogenesis of these cancers. Similar to cutaneous melanoma, the pathogenesis of BCC, CSCC, and virus-negative MCC is related to DNA damage from ultraviolet radiation exposure, and these cancers have a very high tumor mutational burden, which likely results in higher levels of tumor neoantigens that may be targets for the immune system. Viral antigens in virus-positive MCC are also strongly immunogenic. Emerging data from clinical trials of immune checkpoint inhibitors in NMSCs look very promising and are rapidly changing the treatment landscape of these cancers. Specifically, pembrolizumab and avelumab are U.S. Food and Drug Administration-approved for treatment of metastatic MCC and cemiplimab for metastatic CSCC. Several ongoing trials are investigating novel immunotherapies (monotherapies as well as combination) for treatment of NMSCs.

Decreased survival and increased recurrence in Merkel cell carcinoma significantly linked with immunosuppression

BACKGROUND

Merkel cell carcinoma (MCC) is a rare and aggressive form of skin cancer. It is an immunogenic tumor as evident by its association with Polyomavirus, immunotherapy response, and increased prevalence in the immunosuppressed population.

OBJECTIVE

We sought to evaluate the impact of known clinicopathological determinants and immunosuppression on the risk of recurrence and mortality of MCC patients.

METHODS

A retrospective, observational cohort study of patients diagnosed and/or treated with MCC at two tertiary academic institutions. We compared clinicopathological determinants, treatment modalities, and immunosuppression status on clinical outcomes of recurrence, disease-specific survival, and overall survival.

RESULTS

We evaluated 90 patients within our study and 34% had a cancer recurrence during follow-up. Patients with recurrence were significantly more likely to be immunosuppressed (32% vs 5%; P = .001). Estimated 5-year recurrence was 43%, and immunosuppressed patients were significantly more likely to recur (Hazard ratio [HR] 3.67 [1.80-7.51]; P < .0001). Immunosuppressed patients had significantly elevated cancer-specific mortality (HR 6.11[1.61-23.26]; P = .008).

LIMITATIONS

Retrospective review with a prolonged observation period and changing treatment modalities.

CONCLUSION

Immunocompromised patients had a threefold increased incidence of 5-year mortality and over twofold increased incidence of any recurrence as non-immunocompromised patients. Patients' immunosuppressive status should be considered when making decisions regarding treatment, surveillance, and prognostication.

miR-205: A Potential Biomedicine for Cancer Therapy

microRNAs (miRNAs) are a class of small non-coding RNAs that regulate the expression of their target mRNAs post transcriptionally. miRNAs are known to regulate not just a gene but the whole gene network (signaling pathways). Accumulating evidence(s) suggests that miRNAs can work either as oncogenes or tumor suppressors, but some miRNAs have a dual nature since they can act as both. miRNA 205 (miR-205) is one such highly conserved miRNA that can act as both, oncomiRNA and tumor suppressor. However, most reports confirm its emerging role as a tumor suppressor in many cancers. This review focuses on the downregulated expression of miR-205 and discusses its dysregulation in breast, prostate, skin, liver, gliomas, pancreatic, colorectal and renal cancers. This review also confers its role in tumor initiation, progression, cell proliferation, epithelial to mesenchymal transition, and tumor metastasis. Restoration of miR-205 makes cells more sensitive to drug treatments and mitigates drug resistance. Additionally, the importance of miR-205 in chemosensitization and its utilization as potential biomedicine and nanotherapy is described. Together, this review research article sheds a light on its application as a diagnostic and therapeutic marker, and as a biomedicine in cancer.

Gene expression profile identifies distinct molecular subtypes and potential therapeutic genes in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare primary cutaneous neoplasm of neuroendocrine carcinoma of the skin. About 80% of the MCC occurs due to Merkel cell polyomavirus (MCPyV) and 20% of the tumors usually occur due to severe UV exposure which is a more aggressive type of MCC. It tends to have an increased incidence rate among elderly and immunosuppressed individuals. On therapeutic level, sub-classification of MCC through molecular subtyping has emerged as a promising technique for MCC prognosis. In current study, two consistent distinct molecular subtypes of MCCs were identified using gene expression profiling data. Subtypes I MCCs were associated with spliceosome, DNA replication and cellular pathways. On the other hand, genes overexpressed in subtype II were found active in TNF signalling pathway and MAPK signalling pathway. We proposed different therapeutic targets based on subtype specificity, such as PTCH1, CDKN2A, AURKA in case of subtype I and MCL1, FGFR2 for subtype II. Such findings may provide fruitful knowledge to understand the intrinsic subtypes of MCCs and the pathways involved in distinct subtype oncogenesis, and will further advance the knowledge in developing a specific therapeutic strategy for these MCC subtypes.

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Merkel cell carcinoma (MCC) a rare and highly aggressive neuroendocrine carcinoma of the skin

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Sub-classification of MCC through molecular subtyping

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Identification of two distinct molecular subtypes of MCCs using gene expression profiling data

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Classification of different therapeutic targets based on subtype specificity

Polyomavirus-driven Merkel cell carcinoma: Prospects for therapeutic vaccine development

Great strides have been made in cancer immunotherapy including the breakthrough successes of anti-PD-(L)1 checkpoint inhibitors. In Merkel cell carcinoma (MCC), a rare and aggressive skin cancer, PD-(L)1 blockade is highly effective. Yet, ~50% of patients either do not respond to therapy or develop PD-(L)1 refractory disease and, thus, do not experience long-term benefit. For these patients, additional or combination therapies are needed to augment immune responses that target and eliminate cancer cells. Therapeutic vaccines targeting tumor-associated antigens, mutated self-antigens, or immunogenic viral oncoproteins are currently being developed to augment T-cell responses. Approximately 80% of MCC cases in the United States are driven by the ongoing expression of viral T-antigen (T-Ag) oncoproteins from genomically integrated Merkel cell polyomavirus (MCPyV). Since T-Ag elicits specific B- and T-cell immune responses in most persons with virus-positive MCC (VP-MCC), and ongoing T-Ag expression is required to drive VP-MCC cell proliferation, therapeutic vaccination with T-Ag is a rational potential component of immunotherapy. Failure of the endogenous T-cell response to clear VP-MCC (allowing clinically evident tumors to arise) implies that therapeutic vaccination will need to be potent anśd synergize with other mechanisms to enhance T-cell activity against tumor cells. Here, we review the relevant underlying biology of VP-MCC, potentially applicable therapeutic vaccine platforms, and antigen delivery formats. We also describe early successes in the field of therapeutic cancer vaccines and address several clinical scenarios in which VP-MCC patients could potentially benefit from a therapeutic vaccine.

Molecular Mechanisms of Merkel Cell Polyomavirus Transformation and Replication

Viral infection underlies a significant share of the global cancer burden. Merkel cell polyomavirus (MCPyV) is the newest member of the human oncogenic virus family. Its discovery over a decade ago marked the beginning of an exciting era in human tumor virology. Since then, significant evidence has emerged to support the etiologic role of MCPyV in Merkel cell carcinoma (MCC), an extremely lethal form of skin cancer. MCPyV infection is widespread in the general population. MCC diagnoses have tripled over the past 20 years, but effective treatments are currently lacking. In this review, we highlight recent discoveries that have shaped our understanding of MCPyV oncogenic mechanism and host cellular tropism, as well as the molecular events occurring in the viral infectious life cycle. These insights will guide future efforts in developing novel virus-targeted therapeutic strategies for treating the devastating human cancers associated with this new tumorigenic virus.

Merkel Cell Carcinoma Treatment in Finland in 1986-2016-A Real-World Data Study

Merkel cell carcinoma (MCC) is a rare cutaneous carcinoma that has gained enormous interest since the discovery of Merkel cell polyoma virus, which is a causative oncogenic agent in the majority of MCC tumours. Increased research has focused on effective treatment options with immuno-oncology. In this study, we reviewed the real-world data on different treatments given to MCC patients in Finland in 1986-2016. We used the Finnish Cancer Registry database to find MCC patients and the Hospital Discharge Register and the Cause-of-Death Register to obtain treatment data. We identified 376 MCC patients and 33 different treatment entities and/or combinations of treatment. An increase was noted in the incidence of MCC since 2005. Therefore, the cohort was divided into two groups: the "early" group with time of diagnosis between years 1986 and 2004 and the "late" group with time of diagnosis between 2005 and 2016. The multitude of different treatment combinations is a relatively new phenomenon; before the year 2005, only 11 treatments or treatment combinations were used for MCC patients. Our data show that combining radiation therapy with simple excision provided a survival advantage, which was, however, lost after adjustment for stage or age. Our registry study serves as a baseline treatment efficacy comparison as we move into the age of immunotherapy in MCC. Standardizing the treatment of MCC patients in Finland requires more work on awareness and multidisciplinary co-operation.

Landscape of current and future therapies of Merkel cell carcinoma

Merkel cell carcinoma is rare and aggressive skin cancer, which occurrence is linked to exposure to ultraviolet light and the Merkel-cell polyomavirus. In recent years, significant progress in understanding the mechanism of Merkel cell carcinoma pathogenesis has been observed. This neoplasm often expresses PD-L1, and MCPyV-specific T cells can express PD-1 thus PD-1/PD-L1 checkpoint therapies seem to be remarkably interesting treatment options. Many clinical trials are currently being conducted to confirm their effectiveness and safety for this group of patients. However, only about half of advanced Merkel cell carcinoma patients could achieve remission or disease stabilization through PD-1/PD-L1 checkpoint therapies thus innovative treatments are still needed. In this article, we have presented current and future directions in the development of Merkel cell carcinoma therapy.

A case of Merkel cell carcinoma of the head and neck

Merkel cell carcinoma (MCC) is a relatively rare and aggressive cutaneous neuroendocrine malignancy. It is characterized by high rates of recurrence and metastasis, both to regional lymph nodes and to distant locations. Its characteristic clinical manifestation is a single, painless, hard, erythematous nodule on a sun-exposed area, particularly in older men. Surgical management of both the primary site and the sentinel lymph node is the standard of care. In this article, we describe the diagnosis and treatment of a case of MCC in the left cheek.

Merkel Cell Carcinoma in the HIV-1/AIDS Patient

Merkel cell carcinoma (MCC) is a highly aggressive, primary neuroendocrine cancer of the skin. The majority of MCC cases are associated with the recently discovered Merkel cell polyomavirus (MCPyV), while the remaining are caused by ultraviolet (UV) light-induced mutations from excessive sunlight exposure. The risk of developing MCC is much higher in the white population relative to all other races. Approximately 10% of all patients with MCC have some form of immunosuppression including HIV-1/AIDS, chronic inflammatory conditions, solid organ transplantation, or hematological malignancies. The age of onset of MCC is lower and the mortality is higher in immunosuppressed individuals than in immune-competent patients. It is plausible that HIV-1/AIDS predisposes to virus-positive MCC, but it should be noted that HIV-1/AIDS increases the risk for developing of UV-induced skin cancers such as cutaneous squamous cell carcinoma and basal cell carcinoma and therefore may also increase the risk for virus-negative MCC. Surgical management is considered standard of care for localized Merkel cell carcinoma with current recommendations advising a wide local excision of the lesion. Most international guidelines support the use of local adjuvant radiotherapy coupled with tumor staging to improve the frequency of cure. For advanced, metastatic, and recurrent MCC, checkpoint blockade inhibitors targeting PD-1 and PD-L1 have shown remarkable activity including durable long-term. MCC in patients living with HIV-1/AIDS are treated with similar modalities as HIV-1 uninfected individuals with MCC.

Molecular and immune targets for Merkel cell carcinoma therapy and prevention

Merkel cell carcinoma (MCC) is a rare neuroendocrine carcinoma of the skin, for which the exact mechanisms of carcinogenesis remain unknown. Therapeutic options for this highly aggressive malignancy have historically been limited in both their initial response and response durability. Recent improvements in our understanding of MCC tumor biology have expanded therapeutic options for these patients, namely through the use of immunotherapies such as immune checkpoint inhibitors. Further elucidation of the tumor mutational landscape has identified molecular targets for therapies, which have demonstrated success in other cancer types. In this review, we discuss both current and investigational immune and molecular targets of therapy for MCC.

The biology and treatment of Merkel cell carcinoma: current understanding and research priorities

Merkel cell carcinoma (MCC) is a rare and aggressive skin cancer associated with advanced age and immunosuppression. Over the past decade, an association has been discovered between MCC and either integration of the Merkel cell polyomavirus, which likely drives tumorigenesis, or somatic mutations owing to ultraviolet-induced DNA damage. Both virus-positive and virus-negative MCCs are immunogenic, and inhibition of the programmed cell death protein 1 (PD-1)–programmed cell death 1 ligand 1 (PD-L1) immune checkpoint has proved to be highly effective in treating patients with metastatic MCC; however, not all patients have a durable response to immunotherapy. Despite these rapid advances in the understanding and management of patients with MCC, many basic, translational and clinical research questions remain unanswered. In March 2018, an International Workshop on Merkel Cell Carcinoma Research was held at the US National Cancer Institute, at which academic, government and industry experts met to identify the highest-priority research questions. Here, we review the biology and treatment of MCC and report the consensus-based recommendations agreed upon during the workshop.

Merkel cell carcinoma (MCC) is a rare and aggressive form of nonmelanoma skin cancer. The availability of immune checkpoint inhibition has improved the outcomes of a subset of patients with MCC, although many unmet needs continue to exist. In this Consensus Statement, the authors summarize developments in our understanding of MCC while also providing consensus recommendations for future research.

ALK and EGFR expression by immunohistochemistry are associated with Merkel cell polyomavirus status in Merkel cell carcinoma

AIMS

Merkel cell carcinoma, a rare cutaneous neuroendocrine tumour of the skin, can be categorised into two groups according to Merkel cell polyomavirus (MCV) presence. MCV-negative tumours are more aggressive and frequently associated with gene mutations. Some of the genes are potential therapeutic targets. We have previously reported EGFR mutations in six of 27 MCC tumours and overexpression of ALK and EZH2 at mRNA level in MCC tumours. In this study, we sought to determine expression of ALK, EGFR and EZH2 in MCC samples and assess their correlation to MCV status and clinical parameters.

METHODS AND RESULTS

Tissue microarrays were utilised and stained with primary antibodies. Staining data were statistically compared to patient sex, tumour location and development of metastasis and MCC-specific death; 112 tumours and their corresponding patient data were included. We found strong expression of ALK in 51% and strong expression of EZH2 in 76% of the tumours. There was evident correlation of ALK expression with MCV-positivity. Expression of EGFR was infrequent, presenting only in seven MCV-negative tumours. None of the proteins associated with development of metastasis or MCC specific death.

CONCLUSIONS

ALK and EZH2 expression are frequent in MCC and ALK expression correlates to MCV positivity. EGFR positive tumours might respond to EGFR inhibiting treatment.

Spontaneous Regression of Merkel Cell Carcinoma of the Male Breast with Ongoing Immune Response

Merkel cell carcinoma (MCC) is a rare cutaneous neuroendocrine tumor arising predominantly on sun-exposed skin among the elderly. The most common location is the head and neck, followed by the extremities. MCCs are highly aggressive tumors and rarely undergo spontaneous regression. We report a case of MCC which presented as a painless breast lump in an elderly male where the tumor regressed spontaneously after a biopsy.

MicroRNAs as Potential Biomarkers in Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare and aggressive type of skin cancer associated with a poor prognosis. This carcinoma was named after its presumed cell of origin, the Merkel cell, which is a mechanoreceptor cell located in the basal epidermal layer of the skin. Merkel cell polyomavirus seems to be the major causal factor for MCC because approximately 80% of all MCCs are positive for viral DNAs. UV exposure is the predominant etiological factor for virus-negative MCCs. Intracellular microRNA analysis between virus-positive and virus-negative MCC cell lines and tumor samples have identified differentially expressed microRNAs. Comparative microRNA profiling has also been performed between MCCs and other non-MCC tumors, but not between normal Merkel cells and malignant Merkel cells. Finally, Merkel cell polyomavirus encodes one microRNA, but its expression in virus-positive MCCs is low, or non-detectable or absent, jeopardizing its biological relevance in tumorigenesis. Here, we review the results of microRNA studies in MCCs and discuss the potential application of microRNAs as biomarkers for the diagnosis, progression and prognosis, and treatment of MCC.

Merkel cell polyomavirus and Merkel cell carcinoma

Merkel cell polyomavirus (MCPyV) causes the highly aggressive and relatively rare skin cancer known as Merkel cell carcinoma (MCC). MCPyV also causes a lifelong yet relatively innocuous infection and is one of 14 distinct human polyomaviruses species. Although polyomaviruses typically do not cause illness in healthy individuals, several can cause catastrophic diseases in immunocompromised hosts. MCPyV is the only polyomavirus clearly associated with human cancer. How MCPyV causes MCC and what oncogenic events must transpire to enable this virus to cause MCC is the focus of this essay.This article is part of the themed issue 'Human oncogenic viruses'.

A short-term in vivo model for Merkel Cell Carcinoma

In vivo tumor models are essential for studying the biology of cancer, identifying tumor targets and evaluating antitumor drugs. Considering the request for the minimisation of animal experiments and following the "3R"-rule ("replacement," "refinement," "reduction"), it has become crucial to develop alternative experimental models in cancer biology. Several studies have already described the avian chorioallantoic membrane (CAM) model as an alternative to rodents, suitable to investigate growth, progression and metastasis of various types of cancer. In the present work, we grafted three Merkel cell carcinoma (MCC) cell lines onto the avian CAM and monitored tumor growth and development of solid tumor nodules. Morphology of xenograft was characterised histologically and immunohistochemically. Our results demonstrate CAM assay as a useful tool to study MCC pathophysiology.

Merkel cell carcinoma: An update and review: Pathogenesis, diagnosis, and staging

Merkel cell carcinoma (MCC) is an uncommon primary cutaneous neuroendocrine cancer. It most commonly presents as an indurated plaque or nodule on sun-damaged skin in elderly patients and is characterized by high rates of local recurrence and nodal metastasis. Survival at 5 years is 51% for local disease and as low as 14% for distant disease, which underscores the aggressive nature of this tumor and challenges in management. Advances in immunology and molecular genetics have broadened our understanding of the pathophysiology of MCC and expanded our therapeutic arsenal. With this comprehensive review, we provide an update of MCC epidemiology, pathogenesis, clinical presentation, diagnostic evaluation and prognostic markers. The second article in this continuing medical education series explores the evolving landscape in MCC management.

Merkel Cell Carcinoma of the Head and Neck: Recommendations for Diagnostics and Treatment

Background

Merkel cell carcinoma (MCC) is a rare, aggressive tumor that often occurs in the head and neck region. Because of these features, the classifications and diagnostic and treatment regimens are frequently modified. Especially in the anatomically complex head and neck region, it is crucial to be aware of the current recommendations for diagnostics and treatment of MCC to ensure appropriate treatment. This overview aims to summarize the currently available literature.

Methods

The authors reviewed the relevant literature and international guidelines for MCC from 2012 to 2017 with respect to epidemiology and prognosis, diagnostic procedures and imaging, surgery, radiation, systemic treatment, and aftercare. These results were compared with existing guidelines, some of them current, and recommendations were derived.

Results

Marked developments in imaging have resulted in an increased use of functional imaging. The surgical concepts have changed regarding safety margins and the use of sentinel node biopsies. In systemic treatment, a move from conventional agents toward immuno-oncology can be observed.

Conclusions

For staging, it is important to be as exact as possible using functional imaging (e.g., positron emission tomography/computed tomography scan), especially in the head and neck area with its complex lymph drainage. This often plays an especially important role in early stages of the tumor, when the resection margin can be reduced to preserve the organ. Aftercare also should include functional imaging. In an advanced, metastatic stage, immuno-oncology (PD-1, PD-L1, CTLA-4) is superior to the previous methods of systemic treatment.

Increased expression of EZH2 in Merkel cell carcinoma is associated with disease progression and poorer prognosis

Enhancer of zeste homolog 2 (EZH2) is a histone methyltransferase that affects tumorigenesis by epigenetic gene silencing. Merkel cell carcinoma (MCC) is a rare cutaneous neuroendocrine carcinoma that has a high risk of disease progression with nodal and distant metastases. Here, we evaluated EZH2 expression by immunohistochemistry in a cohort of 85 MCC tumors (29 primary tumors, 41 lymph node metastases, 13 in-transit metastases, and 2 distant metastases) with clinical follow-up. We show strong/moderate EZH2 expression in 54% of tumors. Importantly, weak expression of EZH2 in the primary tumor, but not nodal metastases, correlated with improved prognosis compared to moderate/strong EZH2 expression (5-year MCC-specific survival of 68% versus 22%, respectively, P=.024). In addition, EZH2 was expressed at higher levels in nodal metastases compared to primary tumors (P=.005). Our data demonstrate that EZH2 has prognostic value and may play an oncogenic role in MCC.

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.

Update on Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous neuroendocrine malignancy. Merkel cell polyomavirus, a tumorigenic DNA virus, is present in most MCC tumors, with implications for tumor biology, diagnosis, and management. Merkel cell polyomavirus-negative tumors have a high burden of UV-signature mutations, similar to melanoma. The histopathologic diagnosis of MCC requires immunohistochemistry to exclude morphologically similar entities. Therapies for advanced disease are currently lacking. Here, the features of MCC are reviewed, including recent molecular discoveries with implications for improved therapy for advanced disease.