The etiology and epidemiology of merkel cell carcinoma

Merkel cell carcinoma: 30-year experience from a single institution

BACKGROUND

Merkel cell carcinoma (MCC) is a rare cutaneous malignancy. Few single-institution series have been reported.

METHODS

Review of MCC patients treated at our institution between 1980 and 2010. Patient, tumor, and treatment variables were analyzed to determine MCC-specific outcomes.

RESULTS

We identified 161 patients with MCC. There was a 2.5-fold increase in cases over the last decade. Median length of follow-up was 36 months. Stage at diagnosis was I in 35 %, II in 21 %, IIIa in 12 %, IIIb in 23 %, and IV in 9 %. The 5-year MCC-specific survival rates were 87, 63, 42, and 0 % for stages I, II, III, and IV, respectively. Death from the disease occurred in 10 % of patients with T1 and in 50 % with larger lesions. One-third of patients presented with nodal disease. Sentinel lymph node biopsy (SLNB) identified micrometastases in 9 out of 27 (33 %) early-stage patients. Recurrence developed in 56 % of SLNB-positive and 39 % of SLNB-negative patients. Half of patients recurred after a median time of 9 months. Proportions of first recurrence location were distant (52 %), nodal (27 %), and local (21 %). Adjuvant treatments did not improve recurrence or survival rates. One-third of patients died of the disease.

CONCLUSIONS

SLNB identifies micrometastasis in one-third of early-stage patients. Negative SLNB may predict for improved but not necessarily favorable outcome. Initial tumor size and clinical nodal disease predict for poor outcome. High recurrence rates warrant the development of more effective adjuvant therapies, and better markers of recurrence and treatment response for MCC are needed.

Discovery of a novel polyomavirus in acute diarrheal samples from children

Polyomaviruses are small circular DNA viruses associated with chronic infections and tumors in both human and animal hosts. Using an unbiased deep sequencing approach, we identified a novel, highly divergent polyomavirus, provisionally named MX polyomavirus (MXPyV), in stool samples from children. The ∼5.0 kB viral genome exhibits little overall homology (<46% amino acid identity) to known polyomaviruses, and, due to phylogenetic variation among its individual proteins, cannot be placed in any existing taxonomic group. PCR-based screening detected MXPyV in 28 of 834 (3.4%) fecal samples collected from California, Mexico, and Chile, and 1 of 136 (0.74%) of respiratory samples from Mexico, but not in blood or urine samples from immunocompromised patients. By quantitative PCR, the measured titers of MXPyV in human stool at 10% (weight/volume) were as high as 15,075 copies. No association was found between the presence of MXPyV and diarrhea, although girls were more likely to shed MXPyV in the stool than boys (p=0.012). In one child, viral shedding was observed in two stools obtained 91 days apart, raising the possibility of chronic infection by MXPyV. A multiple sequence alignment revealed that MXPyV is a closely related variant of the recently reported MWPyV and HPyV10 polyomaviruses. Further studies will be important to determine the association, if any, of MXPyV with disease in humans.

Strategy for eliciting antigen-specific CD8+ T cell-mediated immune response against a cryptic CTL epitope of merkel cell polyomavirus large T antigen

Background

Merkel cell carcinoma (MCC) is a relatively new addition to the expanding category of oncovirus-induced cancers. Although still comparably rare, the number of cases has risen dramatically in recent years. Further complicating this trend is that MCC is an extremely aggressive neoplasm with poor patient prognosis and limited treatment options for advanced disease. The causative agent of MCC has been identified as the merkel cell polyomavirus (MCPyV). The MCPyV-encoded large T (LT) antigen is an oncoprotein that is theorized to be essential for virus-mediated tumorigenesis and is therefore, an excellent MCC antigen for the generation of antitumor immune responses. As a foreign antigen, the LT oncoprotein avoids the obstacle of immune tolerance, which normally impedes the development of antitumor immunity. Ergo, it is an excellent target for anti-MCC immunotherapy. Since tumor-specific CD8+ T cells lead to better prognosis for MCC and numerous other cancers, we have generated a DNA vaccine that is capable of eliciting LT-specific CD8+ T cells. The DNA vaccine (pcDNA3-CRT/LT) encodes the LT antigen linked to a damage-associated molecular pattern, calreticulin (CRT), as it has been demonstrated that the linkage of CRT to antigens promotes the induction of antigen-specific CD8+ T cells.

Results

The present study shows that DNA vaccine-induced generation of LT-specific CD8+ T cells is augmented by linking CRT to the LT antigen. This is relevant since the therapeutic effects of the pcDNA3-CRT/LT DNA vaccine is mediated by LT-specific CD8+ T cells. Mice vaccinated with the DNA vaccine produced demonstrably more LT-specific CD8+ T cells. The DNA vaccine was also able to confer LT-specific CD8+ T cell-mediated protective and therapeutic effects to prolong the survival of mice with LT-expressing tumors. In the interest of determining the LT epitope which most MCC-specific CD8+ T cells recognize, we identified the amino acid sequence of the immunodominant LT epitope as aa19-27 (IAPNCYGNI) and found that it is H-2k^b-restricted.

Conclusion

The results of this study can facilitate the development of other modes of MCC treatment such as peptide-based vaccines and adoptive transfer of LT-specific CD8+ T cells. Likewise, the MCC DNA vaccine has great potential for clinical translation as the immunologic specificity is high and the treatment strategy can be exported to address other virus-induced tumors.

Uncommon cutaneous neoplasms of the head and neck

This article concentrates on the less-common cutaneous malignancies such as merkel cell, atypical fibroxanthoma, malignant fibrous histiocytoma, dermatofibrosarcoma protuberans, microcystic adnexal carcinoma, and sebaceous carcinoma. The clinical and histopathologic descriptions of each, most current and emerging etiologies, diagnosis, staging, treatment, and prognosis are discussed.

Defective DNA repair and cell cycle arrest in cells expressing Merkel cell polyomavirus T antigen

The pathways by which Merkel cell polyomavirus (MCV) infection contributes to the formation of Merkel cell carcinomas are important for understanding the pathogenesis of these cancers. We hypothesized that MCV T antigen suppresses normal responses to ultraviolet radiation (UVR)-induced DNA damage. An MCV-infected cell line (MKL-1) exhibited UVR hypersensitivity, impaired repair of DNA lesions and cell cycle arrest after UVR, as well as reduced levels of the DNA damage recognition protein, XPC. When ectopically expressed in uninfected UISO cells, mutant but not wild-type T antigen resulted in loss of repair of UVR-induced cyclobutane pyrimidine dimers and reductions in XPC, p53 and p21 levels, whereas both wild-type and mutant T antigen inhibited cell cycle arrest after UVR. Similarly, only mutant T antigen in normal fibroblasts inhibited DNA repair and XPC expression, while both mutant and wild-type T antigens produced cell cycle dysregulation. Wild-type T antigen expression produced large T, 57 kT and small T antigens while mutant T antigen was only detectable as a truncated large T antigen protein. Expression of wild-type large T antigen but not small T antigen inhibited the G1 checkpoint in UISO cells, but neither wild-type large T nor small T antigens affected DNA repair, suggesting that large T antigen generates cell cycle defects, and when mutated may also impair DNA repair. These results indicate that T antigen expression by MCV can inhibit key responses to UVR-induced DNA damage and suggest that progressive MCV-mediated abrogation of genomic stability may be involved in Merkel cell carcinogenesis.

Merkel cell carcinoma: recent insights and new treatment options

PURPOSE OF REVIEW

Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine carcinoma of the skin demonstrating a high propensity of recurrence and metastasis. Its 5-year disease-specific survival rate is only about 60%. Although MCC is still regarded as a very rare tumor entity, its incidence is rapidly increasing. In this regard, the American Cancer Society estimated almost 1500 new cases in the United States in 2008.

RECENT FINDINGS

The newly identified Merkel cell polyomavirus (MCV) has been found associated to most MCC cases. Nevertheless, the distinct molecular pathogenesis of MCC and its link to MCV is not yet fully understood. Moreover, the impact of MCV positivity on the course of disease and prognosis of MCC patients is controversially discussed.

SUMMARY

This review summarizes recent findings on MCC pathogenesis with a special emphasis on the impact of MCV, presents an overview of clinical aspects, and discusses treatment options.

Significant overexpression of the Merkel cell polyomavirus (MCPyV) large T antigen in Merkel cell carcinoma

BACKGROUND

The purpose of this study was to determine the expression pattern of the Merkel cell polyomavirus (MCPyV) large T-protein antigen in patients with Merkel cell carcinoma.

METHODS

A tissue microarray (TMA) containing 30 specimens was constructed and stained for the MCPyV large T protein. Immunohistochemical expression was determined semiquantitively and was compared to patients' outcome.

RESULTS

Nuclear expression of MCPyV large T protein was detected in 29 of 30 specimens (97%). In particular, 60% to 100%, 30% to 60%, and 10% to 30% of tumor cells were positive in 27 specimens (90%), 1 (3%), and 1 (3%), respectively. There was no difference in positivity between primary and metastatic lesions. Clinical data could not be correlated to MCPyV large T-protein expression.

CONCLUSION

MCPyV large T protein was significantly overexpressed in 97% of all specimens. Although we could not demonstrate a predictive effect, MCPyV large T protein may represent a molecular marker with utility in pathological diagnosis as well as a potential new therapeutic target in patients with Merkel cell carcinoma.

Human polyomavirus related to African green monkey lymphotropic polyomavirus

TOC summary: This virus is shed at the human skin surface.

While studying the virome of the skin surface of a patient with a Merkel cell carcinoma (MCC) by using unbiased, high-throughput sequencing, we identified a human polyomavirus nearly identical to human polyomavirus 9, a virus recently reported in blood and urine of renal transplantion patients and closely related to the African green monkey lymphotropic polyomavirus. Specific PCR analysis further identified this virus in 2/8 patients with MCC but in only 1/111 controls without MCC. This virus was shed for >20 months by the MCC index patient and was on the skin of the spouse of the index patient. These results provide information on the viral ecology of human skin and raise new questions regarding the pathology of virus-associated skin disorders.

Prevalence of polyomaviruses and links with human diseases

The simian virus 40 and murine polyomaviruses were shown to be DNA tumor viruses in their natural hosts and/or heterologous experimental hosts in the mid-20th Century. The first two human polyomaviruses, the BK polyomavirus and JC polyomavirus, were discovered in 1971 and were shown to induce severe disease in immunocompromised patients, but their involvement in human cancers is still a matter for debate. The discovery of a polyomavirus associated with Merkel cell carcinoma (Merkel cell polyomavirus) in 2008 resulted in a renewed interest in the Polyomaviridae family, leading to the discovery of new human polyomaviruses. This review addresses the involvement of the nine human polyomaviruses and simian virus 40 in human diseases, with a particular focus on their prevalence and the humoral response directed against structural antigens in the general population and in subjects presenting specific diseases.

Merkel cell carcinoma: a population-based study on mortality and the association with other cancers

Background

Few population-based epidemiological data are available on Merkel cell carcinoma (MCC), a rare lethal non-melanoma skin cancer. We analysed multiple-cause-of-death records to describe MCC mortality and trends and the association with other primary cancers.

Methods

We reviewed all 6,713,059 death certificates in Italy (1995–2006) to identify those mentioning MCC. We evaluated the association with other primary cancers by calculating the ratio of observed to expected deaths, using a standardized mortality ratio (SMR)-like analysis. We also evaluated the geographic distribution of deaths.

Results

We identified 351 death certificates with the mention of MCC. The age-adjusted mortality was 0.031/100,000, with a significant trend of increase and a slight north–south gradient. There was a significant deficit for solid cancers (SMR = 0.15) and a non-significant excess for lymphohematopoietic malignancies (SMR = 1.62). There were significant excesses for chronic lymphocytic leukemia (SMR = 4.07) and Waldenström’s macroglobulinemia (SMR = 27.2) and a non-significant excess for chronic myeloid leukemia (SMR = 5.12).

Conclusions

The increase in MCC mortality reflects the incidence trend in the literature. The association with chronic lymphocytic leukemia confirms the importance of immunologic factors in MCC. Regarding Waldenström’s macroglobulinemia, an association with MCC has never been reported.

An intact retinoblastoma protein-binding site in Merkel cell polyomavirus large T antigen is required for promoting growth of Merkel cell carcinoma cells

Merkel cell carcinoma (MCC) is a highly aggressive skin cancer that frequently harbours Merkel cell polyomavirus (MCV) DNA integrated in the genome of the tumor cells. In our study, we elaborate our recent finding that MCV-positive MCC cell lines require the expression of the viral T antigens (TA). Indeed, in a xeno-transplantation model, we prove that TA expression is essential also in an in vivo situation, as knock down of TA leads to tumor regression. Moreover, rescuing TA short hairpin RNA (shRNA)-treated MCV-positive MCC cells by ectopic expression of shRNA-insensitive TAs clearly demonstrates that the observed effect is caused by TA knockdown. Notably, introduction of a mutation in the LTA protein interfering with LTA binding to the retinoblastoma protein (RB) ablated this rescue. The importance of this interaction was further confirmed as LTA-specific knockdown leads to explicit cell growth inhibition. In summary, the presented data demonstrate that established MCV-positive MCC tumors critically depend on TA expression, in particular the LTA and RB interaction, for sustained tumor growth. Consequently, interference with LTA/RB interaction appears as promising strategy to treat MCC.

High Levels of Antibodies Against Merkel Cell Polyomavirus Identify a Subset of Patients With Merkel Cell Carcinoma With Better Clinical Outcome

Purpose

A new human polyomavirus, Merkel cell polyomavirus (MCV), was identified in 2008 in tumor tissue of patients with Merkel cell carcinoma (MCC), a relatively rare human skin cancer. In this study, we investigated patients with MCC and controls for the presence of antibodies against MCV and their association with clinical characteristics.

Patients and Methods

Antibodies against MCV were investigated by enzyme-linked immunosorbent assay in 68 patients with MCC and 82 controls using VP1 virus-like particles produced in insect cells.

Results

Antibodies against MCV were detected in all patients with MCC and in 85% of controls. However, high antibody titers (> 10,000) were rarely observed in controls (7.3%) and they were detected in 64.7% of patients with MCC (P < .001) in contrast to the absence of VP1 expression in tumor samples. In addition, the geometric mean titer of anti-MCV in patients with MCC was around 14 times higher than that observed in MCV-positive controls (P < .001) and was not correlated with tumor viral load. High antibody titers were not found to be associated with any subject or tumor characteristics, but better progression-free survival was observed in patients with high antibody titers (hazard ratio, 4.6; 95% CI, 1.7 to 12.2; P = .002).

Conclusion

High titers of MCV antibodies in a much higher proportion of patients with MCC than in controls confirmed the association between MCV infection and MCC. The findings also indicated that a better progression-free survival occurred in patients with high MCV antibody titers and suggested that there are at least two distinct etiologic causes of MCC.

Immunohistochemistry for Merkel cell polyomavirus is highly specific but not sensitive for the diagnosis of Merkel cell carcinoma in the Australian population

Recent studies have demonstrated a high frequency of detection of Merkel cell polyomavirus in Merkel cell carcinoma. However, most of these studies are from European or North American centers that have relatively low sun exposure and may have a higher incidence of virus-driven oncogenesis compared with the highly sun-exposed but predominantly fair-skinned Australian population. We performed immunohistochemistry for Merkel cell polyomavirus on 104 cases of Merkel cell carcinoma and 74 cases of noncutaneous small cell-undifferentiated carcinoma from 3 major Australian centers. Nineteen (18.3%) cases of Merkel cell carcinoma showed positive staining for Merkel cell polyomavirus versus 1 (1.3%) of small cell-undifferentiated carcinoma. All 15 cases (14.3%) of Merkel cell carcinoma with areas of mixed squamous differentiation showed negative staining. We found positive staining in only 3 (7.7%) of 39 Merkel cell carcinoma from the head and neck (the most sun-exposed area) versus 16 (24.6%) of 65 of tumors from other sites (P < .05). Our findings support the concept of a Merkel cell polyomavirus-driven and a non-Merkel cell polyomavirus-driven (primarily sun-dependent) pathway in Merkel cell carcinoma carcinogenesis, with the latter being significantly more frequent in Australia and in mixed squamous-Merkel cell carcinoma (which is also more frequent in Australia). Although immunohistochemistry for Merkel cell polyomavirus seems to be highly specific in all populations, the low incidence of Merkel cell polyomavirus-positive Merkel cell carcinoma in a highly sun-exposed population limits its diagnostic utility in this setting.