The prevalence of Merkel cell polyomavirus in Japanese patients with Merkel cell carcinoma

Prevalence of Merkel Cell Polyomavirus in Normal and Lesional Skin: A Systematic Review and Meta-Analysis

The prevalence of Merkel cell polyomavirus(MCPyV) in Merkel cell carcinoma(MCC) and non-MCC skin lesions and its possible role in the etiology of other skin diseases remain controversial. To systematically assess the association between MCPyV infection and MCC, non-MCC skin lesions, and normal skin. For this systematic review and meta-analysis, a comprehensive search for eligible studies was conducted using Medline Ovid, Pubmed, Web of Science, and the Cochrane CENTRAL databases until August 2021; references were searched to identify additional studies. Observational studies that investigated the association between MCPyV infection and MCC, non-MCC skin lesions, and normal skin using polymerase chain reaction(PCR) as a detection method and provided sufficient data to calculate the prevalence of MCPyV positivity. A total of 50 articles were included in the study after exclusion criteria were applied. Two reviewers independently reviewed and assessed the eligibility of the studies, and all disagreements were resolved by consensus. To determine the association between MCPyV and MCC, overall odds ratio (OR) were calculated with 95% CI using a random-effects model. Single-arm meta-analyses were performed to examine the prevalence rate of MCPyV+ in MCC, non-MCC skin lesions, and normal skin. The primary analysis was the prevalence rate of MCPyV+ in MCC. Secondary outcomes included the prevalence rate of MCPyV+ in non-MCC skin lesions and normal skin. A total of 50 studies involving 5428 patients were reviewed based on our inclusion and exclusion criteria. Compared with the control group, MCPyV infection was significantly associated with MCC (OR = 3.51, 95% CI = 2.96 - 4.05). The global prevalence of MCPyV+ in MCC, melanoma, squamous cell carcinoma, basal cell carcinoma, Bowen's disease, actinic keratosis, keratoacanthoma, seborrheic keratosis, and normal skin was 80%, 4%, 15%, 15%, 21%, 6%, 20%, 10%, and 11%, respectively. The current results suggest that MCPyV infection is significantly associated with an increased risk of MCC. However, the low prevalence rate of MCPyV+ in non-MCC skin lesions does not exclude a pathogenic association of this virus with the development of non-MCC skin lesions.

Evidencing the presence of merkel cell polyomavirus in papillary thyroid cancer

Merkel cell polyomavirus (MCPyV) infects most people asymptomatically, but recent reports indicate that the virus may be related to carcinogenesis. This study aimed to evaluate the impact of MCPyV on the development of papillary thyroid cancer (PTC). Totally, 1057 samples, including 412 fresh biopsy samples (FBS) and 645 paraffin-embedded PTC biopsy samples (PEBS), and 1057 adjacent non-cancerous samples were assessed for the presence of MCPyV DNA and RNA. MCPyV DNA was positive in 215 (20.3%) of samples, including 126 (30.6%) in FBS and 89 (13.8%) in PEBS. In MCPyV-positive samples, the mean MCPyV copy number was higher in the patients with FBS (2.3 × 10-1 ± 0.5 × 10-1 copies/cell) compared to PEBS (0.7 × 10-4 ± 0.1 × 10-4 copies/cell) and adjacent non-PTC normal samples (0.3 × 10-5 ± 0.02 × 10-5 copies/cell), indicating a statistically significant difference (P < 0.001). The LT-Ag RNA expression was higher in FBS compared to PEBS, while VP1 gene transcript was not detected in any samples. Although our findings showed the presence of MCPyV in a subset of PTC Iranian patients, further research is required to confirm these findings.

Tissue Pathogens and Cancers: A Review of Commonly Seen Manifestations in Histo- and Cytopathology

Tissue pathogens are commonly encountered in histopathology and cytology practice, where they can present as either benign mimickers of malignancy or true malignancies. The aim of this review is to provide a timely synthesis of our understanding of these tissue pathogens, with an emphasis on pertinent diagnostic conundrums associated with the benign mimickers of malignancy that can be seen with viral infections and those which manifest as granulomas. The oncogenic pathogens, including viruses, bacteria, and parasites, are then discussed with relationship to their associated malignancies. Although not exhaustive, the epidemiology, clinical manifestations, pathogenesis, and histological findings are included, along with a short review of emerging therapies.

Merkel Cell Polyomavirus Gene Expression and Mutational Analysis of Large Tumor Antigen in Non-Merkel Cell Carcinoma Tumors of Iranian Patients

INTRODUCTION

The presence of Merkel cell polyomavirus (MCPyV) was identified in Merkel cell carcinoma (MCC). However, there was sparse information on the link of other common nonmelanoma skin cancers - basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) - to MCPyV infection. The current study describes the phylogenetic information of MCPyV isolated from Iranian non-MCC (nonmelanoma skin cancers) focusing on tumorigenesis of mutations in large tumor (LT) antigen (LT-Ag) fragment.

METHODS

Sixty patients with BCC and 20 patients with SCC were included in this study (48 males and 32 females; average age 65 years). The MCPyV-DNA copy number in positive samples was measured by quantitative real-time PCR. Then, mutational analysis of the MCPyV LT gene was carried out by direct sequencing.

RESULTS

While MCPyV DNA was detected in 6 (10%) of 60 BCC samples, no viral genome was found in SCCs. There was no distinct association of MCPyV positivity with gender, age, or type of tumor (BCC or SCC) (p value >0.05). Quantitative real-time PCR revealed that the median number of viral DNA copies per cell was 0.7 in 6 MCPyV-positive BCC samples. Furthermore, full-length LT-Ag sequencing of positive samples indicated no stop codon or frameshift mutations compared to reference sequences.

CONCLUSION

Considering the important role of the LT-Ag in the pathogenicity of MCPyV, non-synonymous mutations compared with the reference proteins triggered relevant amino acid substitutions. Overall, the results showed no tumor-associated mutations in the LT-Ag sequence of MCPyVs from positive samples.

Merkel cell polyomavirus is implicated in a subset of Merkel cell carcinomas, in the Indian subcontinent

Merkel cell carcinoma is a rare, lethal cancer histopathologically composed of cells showing similarity with mechanoreceptor Merkel cells. Merkel cell tumors manifest in two distinct forms. While a virus called Merkel cell polyomavirus is involved in the pathogenesis of one form of Merkel tumors, the other is driven by ultraviolet (UV)-linked mutations. In this study we investigated 18 cases, from the Indian population, of Merkel cell carcinoma for immunohistochemical (IHC) expression of Merkel cell polyomavirus (MCV) T antigen, including 12 cases tested by PCR, to identify viral etiopathology. We tested the tumors with two sensitive antibodies (CM2B4 and Ab3), targeting the viral large T antigen protein and with PCR primers targeting the N terminus of T antigen. Overall, we observed 38.8% (7/18) tumors displaying positive IHC expression of Merkel cell polyomavirus T antigen and 25% (3/12) tumors showing positive results, by both, immunohistochemistry and PCR. This constitutes the first report from India showing implication of MCV in Merkel cell carcinomas. Moreover, this is one of the larger series of Merkel cell carcinomas, tested for MCV, by both immunohistochemistry and PCR, in this part of the world. These results further indicate that a slightly more number of such cases in India are likely to be caused by UV-linked damage, as opposed to Merkel cell polyomavirus mediated tumorigenesis, which is definitely implicated in a subset of cases.

Merkel cell carcinoma in Taiwan: A series of 24 cases and literature review

Merkel cell carcinoma (MCC) is a rare but aggressive neuroendocrine carcinoma of the skin. The available reports of MCC in Asia are limited; in this study, we report the largest series of MCC in Taiwan to date.The series is composed by 24 pathologically proven MCC cases, which were retrospectively reviewed in Chang Gung Memorial Hospital in Taiwan between 2000 and 2018.The tumor occurred predominantly in men (80%) and in the elderly (median 74.8 years). Twenty-one patients had locoregional MCC and 3 had metastatic MCC at the time of diagnosis. Patients with pathologically proven negative nodes by sentinel lymph node biopsy (SLNB) showed better survival time than those without SLNB in 16 clinically node-negative MCC cases undergoing primary surgery. Salvage surgery for loco-regional recurrence lengthened the survival time and possibly cured recurrent MCC. Palliative chemotherapy with cisplatin and etoposide showed a response rate of 25%, progression-free survival of 3.6 months, and overall survival of 14.8 months in 4 metastatic/recurrent MCC. Avelumab treatment was effective in 1 patient, who achieved a durable disease control.This observational cohort of MCC patients in Taiwan suggests aggressive surgical intervention including wide excision and lymph node management, salvage operation is critical for early MCC patients, and palliative chemotherapy and immunotherapy showed their efficacy for advanced MCC patients.

Merkel Cell Carcinoma: An Update and Immunotherapy

Merkel cell carcinoma (MCC) is a rare but aggressive skin cancer with frequent metastasis and death. MCC has a mortality rate of 30%, making it more lethal than malignant melanoma, and incidence of MCC has increased almost fourfold over the past 20 years in the USA. MCC has long been considered to be an immunogenic cancer because it occurs more frequently in immunosuppressed patients from organ transplant and HIV infection than in those with immunocompetent. Chronic UV light exposure and clonal integration of Merkel cell polyomavirus (MCPyV) are two major causative factors of MCC. Approximately 80% of MCC are associated with MCPyV, and T cells specific for MCPyV oncoproteins are present in the blood and tumors of patients. Several studies have shown that a subset of MCCs express PD-1 on tumor-infiltrating lymphocytes and express PD-L1 on tumor cells, which suggests an endogenous tumor-reactive immune response that might be unleashed by anti-PD-1 or anti-PD-L1 drugs.

Low viral load of Merkel cell polyomavirus in Iranian patients with head and neck squamous cell carcinoma: Is it clinically important?

Recent studies show that the human Merkel cell polyomavirus (MCPyV) may be involved in causing cancer. The objective of this study was to assess the impact of MCPyV on the development of head and neck squamous cell carcinoma (HNSCC). In total, 50 paraffin-embedded HNSCC biopsy samples and 50 adjacent non-cancerous samples were evaluated for the presence of MCPyV DNA and RNA. Among patients, the five most frequent histopathologic sites were the tongue (22.0%), lip (16.0%), submandibular (14.0%), cheek (14.0%), and throat (14.0%). MCPyV DNA was positive in eight (16.0%) samples. The median MCPyV LT-Ag copy number in the eight positive samples and in one non-cancerous sample was 4.8 × 10-3 and 2.6 × 10-5  copies/cell, respectively. Quantification of MCPyV LT-Ag revealed increased expression in stage III (5.6 × 10-3  copies/cell) than in the other stages. The MCPyV DNA load in different stages of HNSCC was also statistically significant (P = 0.027). The viral load was low, suggesting that only a fraction of cancerous cells is infected. This result provides evidence confirming the presence of MCPyV in a subset of Iranian patients with HNSCCs, but further studies needed to confirm our findings.

Prevalence of cutaneous viral infections in incident cutaneous squamous cell carcinoma detected among chronic lymphocytic leukemia and hematopoietic stem cell transplant patients

The role of cutaneous viral infections in the development of non-melanoma skin cancer (NMSC), including cutaneous squamous cell carcinoma (SCC), among chronic lymphocytic leukemia (CLL) and blood and marrow transplant (BMT) patients is not established. CLL (n = 977) and BMT (n = 3587) patients treated at the Moffitt Cancer Center were included in a retrospective cohort study. Human papillomavirus (HPV) and human polyomavirus (HPyV) DNA were examined in a subset of incident SCC tumors. Five-year cumulative incidence of NMSC was 1.42% in both BMT (n = 31 NMSCs) and CLL (n = 18 NMSCs) cohorts. Of the nine SCC tumors examined from each cohort, 22.2% and 33.3% were positive for viral DNA in the transplant (HPV 65, MCV) and CLL (HPV 38, HPV 15, HPyV6) cohort, respectively. Enhanced skin cancer screening of BMT/CLL patients should be conducted to better capture incident NMSCs and examine the role of viral infections in these tumors.

Age and Gender Associations of Virus Positivity in Merkel Cell Carcinoma Characterized Using a Novel RNA In Situ Hybridization Assay

Purpose: Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine tumor of the skin. Merkel cell polyomavirus (MCPyV) plays an oncogenic role in the majority of MCCs. Detection of MCPyV in MCCs has diagnostic utility and prognostic potential. We investigated whether RNAscope, an RNA in situ hybridization (ISH) assay for detection of RNA transcripts in tissues, is useful for MCPyV detection.Experimental Design: We applied an RNAscope probe targeting MCPyV T antigen transcripts on tissue microarrays (TMA) and whole-tissue sections encompassing 87 MCCs from 75 patients, 14 carcinomas of other types, and benign tissues. For comparison, qPCR was performed on 57 cases of MCC from 52 patients.Results: RNA-ISH demonstrated the presence of MCPyV in 37 of 75 cases (49.3%). Notably, tumors from younger patients (<73 years) had a significantly higher virus positivity than those from elderly patients (≥73 years; 64.9% vs. 34.2%, P = 0.011). Female patients had a higher positive rate of MCPyV than male patients (66.7% vs. 39.6%, P = 0.032). Data from both RNA-ISH and qPCR were available for 57 samples. Considering MCPyV qPCR as the gold standard for determining MCPyV status, RNAscope had 100% sensitivity and 100% specificity. There was a strong correlation between qPCR copy number and RNA-ISH product score (Spearman correlation coefficient R² = 0.932, P < 0.0001).Conclusions: RNA-ISH is comparably sensitive to qPCR for detection of MCPyV and allows for correlation with tissue morphology. This study also reveals a significant association between age, gender, and MCPyV positivity. Clin Cancer Res; 23(18); 5622-30. ©2017 AACR.

Merkel cell carcinoma: Epidemiology, prognosis, therapy and unmet medical needs

Merkel cell carcinoma (MCC) is a rare skin cancer that is associated with Merkel cell polyomavirus infection in most cases. Incidence rates of MCC have increased in past decades. Risk factors for MCC include ultraviolet light exposure, immunosuppression and advanced age. MCC is an aggressive malignancy with frequent recurrences and a high mortality rate, although patient outcomes are generally more favourable if the patient is referred for treatment at an early stage. Although advances have been made recently in the MCC field, large gaps remain with regard to definitive biomarkers and prognostic indicators. Although MCC is chemosensitive, responses in advanced stages are mostly of short duration, and the associated clinical benefit on overall survival is unclear. Recent nonrandomised phase 2 clinical trials with anti-PD-L1/PD-1 antibodies have demonstrated safety and efficacy; however, there are still no approved treatments for patients with metastatic MCC. Patients with advanced disease are encouraged to participate in clinical trials for treatment, indicating the largely unmet need for durable, safe treatment within this population.

Merkel cell carcinoma: Do you know your guidelines?

BACKGROUND

Merkel cell carcinoma (MCC) is a cutaneous neuroendocrine malignancy that exhibits clinically aggressive features and is associated with a poor prognosis. The incidence of MCC seems to be increasing for reasons unknown, and is estimated to be 0.32/100,000 in the United States.

METHODS

This article will review the current literature and National Comprehensive Cancer Network practice guidelines in the treatment of MCC.

RESULTS

Resection of MCC with negative margins remains the mainstay of therapy. Positive nodal disease should be treated with neck dissection and adjuvant radiotherapy. High-risk patients should undergo adjuvant radiotherapy, which improves oncologic outcomes. The role of chemotherapy is less clear and is currently reserved for advanced-stage MCC and palliative therapy.

CONCLUSION

The pathogenesis of MCC has recently been impacted with the discovery of the Merkel cell polyomavirus (MCPyV). Research to establish targeted and immunologic therapeutic options are ongoing.

Merkel cell polyomavirus (MCV) T-antigen seroreactivity, MCV DNA in eyebrow hairs, and squamous cell carcinoma

Background

The role of Merkel cell polyomavirus (MCV) infection in the etiology of non-melanoma skin cancers, other than Merkel cell carcinoma, is unclear. Previously, we reported a significant association between seropositivity to MCV capsid antigen and MCV DNA-positive cutaneous squamous cell carcinoma (SCC). Here we present associations between SCC and seroreactivity to MCV T-antigen (T-Ag) oncoprotein, as well as MCV DNA detected in eyebrow hairs.

Findings

A clinic-based case–control study, including 171 SCC cases and 300 controls without skin cancer, was conducted at Moffitt Cancer Center in Tampa, Florida. Multiplex assays were used to measure serum antibodies against MCV small and large T-Ag and MCV DNA in both eyebrow hairs and SCC tumors (n = 144). Odds ratios (ORs) and 95 % confidence intervals (CIs) were estimated using logistic regression to evaluate the associations between MCV and SCC. No significant association was observed between seroreactivity to MCV full-length large or small T-Ag and SCC, overall [OR_{large T-Ag} = 0.99 (0.48-2.08), OR_{small T-Ag} = 0.31 (0.06–1.62)] or when comparing tumor MCV DNA-positive cases to controls [OR_{large T-Ag} = 1.06 (0.38–2.93)]. Only presence of MCV DNA in eyebrow hairs was significantly associated with MCV DNA-positive SCC [OR = 4.05 (2.01–8.18)].

Conclusion

MCV infection is unlikely to play a direct role in SCC.

Merkel cell carcinoma of the head and neck: pathogenesis, current and emerging treatment options

Merkel cell carcinoma (MCC) is a relatively uncommon, neuroendocrine, cutaneous malignancy that often exhibits clinically aggressive features and is associated with a poor prognosis. It typically presents as a painless, rapidly enlarging, dome-shaped red or purplish nodule in a sun-exposed area of the head and neck or upper extremities. Our understanding of MCC has increased dramatically over the last several years and the pathogenesis continues to be an area of active research. The etiology is likely multifactorial with immunosuppression, UV-induced skin damage, and viral factors contributing to the development of MCC. The recent discovery of Merkel cell polyomavirus has allowed for at least one aspect of disease development to be much better understood. In most cases, treatment consists of wide local excision with adjuvant radiation therapy. The role of chemotherapeutics is still being defined. The recent advancement of knowledge regarding the pathogenesis of MCC has led to an explosion research into novel therapeutic agents and strategies. This review seeks to summarize the current body of literature regarding the pathogenesis of MCC and potential targets for future therapies.

Merkel cell carcinoma and Merkel cell polyomavirus: a systematic review and meta-analysis

Several observational studies have assessed the correlation between Merkel cell carcinoma and Merkel cell polyomavirus with variable results. The objective of this systematic review was to determine whether there is a correlation between Merkel cell carcinoma and Merkel cell polyomavirus. Studies assessing the relationship between Merkel cell carcinoma and Merkel cell polyomavirus from January 2008 to August 2014 were pooled from Medline, Embase, PubMed, Cochrane Database of Systemic Reviews and Google Scholar. From each study we collected the first author's last name, publication year, country of origin, type of study design, characteristics of participants, possible variables incorporated into the multivariable analyses and the risk ratio (RR) for Merkel cell carcinoma associated with Merkel cell polyomavirus combined with the corresponding 95% confidence interval (CI). Methodological assessment of the study was evaluated using the Newcastle-Ottawa scale. Crude RR was calculated from the data provided in each article. Meta-analyses for the global RR and for the proportion of positives in both case and control samples were performed. In addition, in order to explore the sources of heterogeneity among the studies, meta-regression and sensitivity analyses are also provided. A total of 22 studies were identified for the analysis. The pooled RR from random-effects analysis was determined to be 6.32 (95% CI, 4.02-9.93). Global proportions of positive samples were 0.79 (95% CI, 0.72-0.84) and 0.12 (95% CI, 0.08-0.19) in the case and control groups, respectively. The findings support the association between Merkel cell carcinoma and Merkel cell polyomavirus. However, a non-negligible percentage of positive results have been identified in controls. Some caution must be taken in the interpretation of these results because heterogeneity between studies was found.

Natural history of polyomaviruses in men: the HPV infection in men (HIM) study

BACKGROUND

Several new polyomaviruses have been discovered in the last decade, including Merkel cell polyomavirus (MCPyV). Little is known about the natural history of the more recently discovered polyomaviruses. We estimated the incidence, prevalence, and persistence of 9 polyomaviruses (MCPyV, BK polyomavirus, KI polyomavirus, JC polyomavirus, WU polyomavirus, Human polyomavirus 6 [HPyV6], HPyV7, HPyV9, and Trichodysplasia spinulosa-associated polyomavirus) and examined factors associated with MCPyV infection in a prospective cohort of 209 men initially enrolled in the HPV Infection in Men (HIM) study.

METHODS

Participants enrolled at the US site of the HIM study were recruited into a substudy of cutaneous viral infections and followed for a median of 12.6 months. Eyebrow hair and normal skin swab specimens were obtained at each study visit, and the viral DNA load was measured using multiplex polymerase chain reaction.

RESULTS

MCPyV infection showed the highest prevalence (65.1% of normal skin swab specimens and 30.6% of eyebrow hair specimens), incidence (81.7 cases per 1000 person-months among normal skin swab specimens, and 24.1 cases per 1000 person-months among eyebrow hair specimens), and persistence (85.8% of normal skin swab specimens and 58.9% of eyebrow hair specimens) among all polyomaviruses examined. Age of >44 years (odds ratio [OR], 2.11; 95% confidence interval [CI], 1.03-4.33) and Hispanic race (OR, 2.64; 95% CI, 1.01-6.88) were associated with an increased prevalence of MCPyV infection in eyebrow hair and normal skin swab specimens, respectively.

CONCLUSION

MCPyV infection is highly prevalent in adults, with age and race being predisposing factors.

Molecular epidemiology of merkel cell polyomavirus: evidence for geographically related variant genotypes

Merkel cell polyomavirus (MCPyV) is linked to a cutaneous cancer mainly occurring in Caucasians. DNA from skin swabs of 255 adults, originating from the 5 continents, were subjected to MCPyV PCRs. Phylogenetic analyses demonstrate the existence of 5 major geographically related MCPyV genotypes (Europe/North America, Africa [sub-Saharan], Oceania, South America, and Asia/Japan).

Phylogenetic analysis of Merkel cell polyomavirus based on full-length LT and VP1 gene sequences derived from neoplastic tumours in Japanese patients

Most Merkel cell polyomavirus (MCPyV) gene sequences have been reported from Western countries and few data are available for the virus sequences from other geographical areas, especially Asia. Thus, we performed phylogenetic analyses based on the nucleotide sequences of the full-length large T-antigen (LT) and viral protein 1 (VP1) genes derived from a variety of cancers in Japanese patients and compared them with sequences from Caucasians. The LT and VP1 gene-based phylogenetic trees identified two main genetic clades. One clade comprised strains isolated from Caucasians, whereas all of the Japanese tumour-derived MCPyV strains belonged to another clade. These findings confirm that most of the MCPyV strains present in Japan form a clade, distinct from Caucasian strains.

Merkel cell polyomavirus (MCPyV) strains in Japanese merkel cell carcinomas (MCC) are distinct from Caucasian type MCPyVs: genetic variability and phylogeny of MCPyV genomes obtained from Japanese MCPyV-infected MCCs

Most of merkel cell carcinomas (MCC), a rare, aggressive skin cancer with neuroendocrine features, harbor merkel cell polyomavirus (MCPyV). Seroepidemiological studies suggested high prevalence of MCPyV in the human population. More than ten sequence data on MCPyV strains in Japan have been available, whereas most sequence data were detected from patients living in Europe or European ancestry. Analysis of nine almost complete and 19 partial sequences from two oncogenes, small T antigen (ST) and large T antigen (LT) genomes obtained from 32 Japanese MCPyV-infected MCC revealed that each Japanese MCPyV-infected MCC harbored a specific MCPyV strain with some synonymous or, silent mutations and stop codons or deletions, but functional domains of T antigen had no amino acid changes. All stop codons were localized after retinoblastoma protein-binding domain. These Japanese MCPyV strains were very closely interrelated to themselves and a consensus sequence of Japanese strain was generated. Phylogenetic analysis of our nine sequences and 70 other sequences for ST and LT gene registered in GenBank indicated that Japanese or Asian MCPyV strains formed distinct clades from Caucasian clade, and phylogenetic tree of our nine and 75 other sequences for ST gene formed characteristic three clades and showed that all Japanese or Asian strains were included in the dominant clade. These suggested the possibility of geographically related genotypes of MCPyV. The genomic characterization of MCPyV variants will provide an important database and insights for illuminating their evolutional and biological differences.

Merkel cell polyomavirus detection in Merkel cell cancer tumors in Northern Germany using PCR and protein expression

Merkel cell carcinoma is a highly malignant skin cancer which predominantly occurs in elderly and immunocompromised persons. The identification of the Merkel cell polyomavirus (MCPyV) has inaugurated a new understanding of Merkel cell carcinoma pathogenesis. The frequent detection of the virus in Merkel cell carcinoma tissue (70-90%), its monoclonal integration in the tumor cells and the expression of viral oncogenes highly suggest that MCPyV is causally linked to the pathogenesis of the majority of Merkel cell cancer (MCC) cases. Using qualitative and quantitative PCR together with immunohistochemical staining this study aimed at characterizing the presence of MCPyV sequences and viral early gene expression in a cohort of MCC cases (n = 32) selected in Northern Germany. 40-57% of the cases were identified as MCPyV positive with 40.6% of the cases positive by immunohistochemical staining and 51.6-57.6% positive by PCR. Interestingly, in the majority (64%) of LT-Antigen positive tumors only 25-50% of tumor cells express LT-Antigen. These data are in accord with published studies describing heterogeneity in MCPyV viral loads and suggest that detection of MCPyV in Merkel cell carcinoma by PCR should be undertaken using multiple primer pairs.

The Utility of Immunohistochemistry for Providing Genetic Information on Tumors

With advances in immunohistochemical technology and growing knowledge of the molecular genetics of tumors, immunohistochemistry is playing an increasingly important role in providing genetic information for tumors. Specific chromosomal translocations can be demonstrated through detection of the protein product of one of the genes involved in gene fusion (such as BCL2, cyclin D, and ALK). Some mutations can be detected by (1) aberrant localization of the protein product (such as β-catenin and nucleophosmin), (2) abnormal accumulation of the protein product as a result of stabilization of the protein (such as p53), and (3) mutation-specific antibodies directed against the mutant protein (such as isocitrate dehydrogenase gene R132H mutation, epidermal growth factor receptor gene L858R and exon 19 deletion mutations, and BRAF gene V600E mutation). Gene deletion or loss of function can be demonstrated by the loss of immunostaining for the protein product (such as mismatch repair proteins in microsatellite-unstable tumors, E-cadherin in lobular carcinoma of the breast, and INI1 in rhabdoid tumors, atypical teratoid/rhabdoid tumors, and epithelioid sarcomas). Gene amplification can be demonstrated by overexpression of the protein product (such as HER2 in breast and gastric cancers, and MDM2 or CDK4 in well-differentiated/dedifferentiated liposarcomas). Viruses associated with tumors can be demonstrated directly (such as Epstein-Barr virus latent membrane protein-1 in Hodgkin lymphomas, human herpesvirus 8 in Kaposi sarcomas, and Merkel cell polyomavirus in Merkel cell carcinomas) or by a surrogate marker (such as p16 in human papillomavirus infection). In this review, examples are given to illustrate the principles and pitfalls of these applications.