Clinicopathological and immunohistochemical analysis of 20 cases of Merkel cell carcinoma in search of prognostic markers

Merkel Cell Carcinoma: Current Issues Regarding Diagnosis, Management, and Emerging Treatment Strategies

Merkel cell carcinoma (MCC) is a rare but aggressive cutaneous tumor with a predilection for the head and neck of elderly Caucasian patients. Although much less common than melanoma, MCC has higher rates of sentinel lymph node involvement, local and regional recurrences, and mortality. The majority of MCC cases have been linked to the relatively newly discovered Merkel cell polyomavirus, which is a ubiquitous constituent of the skin flora. Recent discoveries regarding viral integration and carcinogenesis and the immunologic features of MCC have expanded the understanding of MCC. These discoveries have led to the development and application of emerging therapies such as somatostatin analogs, immune checkpoint inhibition, adoptive cell therapy, and other exciting possibilities for targeted therapy.

Molecular characteristics and potential therapeutic targets in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine skin tumour occurring preferentially in elderly and immunosuppressed individuals. Multiple studies have provided insight into the molecular alterations of MCC, leading to the design of several ongoing clinical trials testing chemotherapy, targeted therapy and immunotherapy in patients with recurrent or metastatic disease. The results of some of these studies are available, whereas others are eagerly awaited and will likely shed light on the understanding of MCC biology and potentially improve the clinical outcomes of patients with this rare disease.

[Merkel cell carcinoma]

Merkel cell carcinoma (MCC, cutaneous neuroendocrine carcinoma) is a rare form of tumor of unclear histogenesis which predominantly occurs in elderly patients on areas exposed to the sun. A higher incidence and occurrence in younger people is predominantly found in immunosuppressed persons which is why a pathogenetic role is also attributed to immunosuppression in addition to ultraviolet (UV) radiation. Additionally, in 80% of cases clonally integrated polyomavirus (Merkel cell polyomavirus, MCPyV) could be detected. Clinically MCC represents an uncharacteristic tumor. Histopathologically, monomorphic dermal and/or subcutaneous nodes are found consisting of round or oval medium sized cells with a vesicular nucleus and sparse cytoplasm. The neoplastic cells of MCC express cytokeratin (CK) 20 with a dot-like perinuclear accentuation. In addition, pan-CK, neuroendocrine markers (e.g. chromogranin A and synaptophysin), neurofilament proteins, CD56, CD57, Bcl-2, TdT and PAX-5 are immunohistochemically positive. In most cases CM2B4, an antibody against MCPyV is also positive. Expression of p63 has been observed in some of the cases and in some studies was associated with a favorable prognosis. The markers thyroid transcription factor 1, mammalian achaete scute complex like 1, vimentin, S-100 and CK7 are not normally expressed by MCC. The prognosis is primarily dependent on tumor size and the lymph node status. The presence of intralymphatic tumor complexes is associated with a higher rate of local recurrence and lymph node metastasis. A larger number of intratumoral cytotoxic T-lymphocytes is accompanied by a favorable prognosis and the presence of > 50% of K-67+ neoplastic cells with an unfavorable prognosis. Further morphological, phenotypical and genetic factors have not yet been validated in larger cohorts with respect to the prognostic relevance.

Both tumor depth and diameter are predictive of sentinel lymph node status and survival in Merkel cell carcinoma

BACKGROUND

The purposes of this study were 1) to determine the impact of primary tumor-related factors on the prediction of the sentinel lymph node (SLN) status and 2) to identify clinical and pathologic factors associated with survival in Merkel cell carcinoma (MCC).

METHODS

An institutional review board-approved, retrospective review of patients with MCC treated between 1988 and 2011 at a single center was performed. Patients were categorized into 5 groups: 1) negative SLN, 2) positive SLN, 3) clinically node-negative but SLN biopsy not performed, 4) regional nodal disease without a known primary tumor, and 5) primary MCC with synchronous clinically evident regional nodal disease. Factors predictive of the SLN status were analyzed with logistic regressions, and overall survival (OS) and disease-specific survival (DSS) were analyzed with Cox models and competing risk models assuming proportional hazards, respectively.

RESULTS

Three hundred seventy-five patients were analyzed, and 70% were male; the median age was 75 years. The median tumor diameter was 1.5 cm (range, 0.2-12.5 cm), and the median tumor depth was 4.8 mm (range, 0.3-45.0 mm). One hundred ninety-one patients underwent SLN biopsy, and 59 (31%) were SLN-positive. Increasing primary tumor diameter and increasing tumor depth were associated with SLN positivity (P = .007 and P = .017, respectively). Age and sex were not associated with the SLN status. Immunosuppression, increasing tumor diameter, and increasing tumor depth were associated with worse OS (P = .007, P = .003, and P = .025, respectively). DSS differed significantly by group and was best for patients with a negative SLN and worst for those with primary MCC and synchronous clinically evident nodal disease (P = .018).

CONCLUSION

For patients with MCC, increasing primary tumor diameter and increasing tumor depth are independently predictive of a positive SLN, worse OS, and worse DSS. Tumor depth should be routinely reported when primary MCC specimens are being evaluated histopathologically.

Cutaneous squamous and neuroendocrine carcinoma: genetically and immunohistochemically different from Merkel cell carcinoma

Cutaneous neuroendocrine (Merkel cell) carcinoma most often arises de novo in the background of a clonally integrated virus, the Merkel cell polyomavirus, and is notable for positive expression of retinoblastoma 1 (RB1) protein and low expression of p53 compared with the rare Merkel cell polyomavirus-negative Merkel cell carcinomas. Combined squamous and Merkel cell tumors are consistently negative for Merkel cell polyomavirus. Little is known about their immunophenotypic or molecular profile. Herein, we studied 10 combined cutaneous squamous cell and neuroendocrine carcinomas for immunohistochemical expression of p53, retinoblastoma 1 protein, neurofilament, p63, and cytokeratin 20 (CK20). We compared mutation profiles of five combined Merkel cell carcinomas and seven 'pure' Merkel cell carcinomas using targeted next-generation sequencing. Combined tumors were from the head, trunk, and leg of Caucasian males and one female aged 52-89. All cases were highly p53- and p63-positive and neurofilament-negative in the squamous component, whereas RB1-negative in both components. Eight out of 10 were p53-positive, 3/10 p63-positive, and 3/10 focally neurofilament-positive in the neuroendocrine component. Six out of 10 were CK20-positive in any part. By next-generation sequencing, combined tumors were highly mutated, with an average of 48 mutations per megabase compared with pure tumors, which showed 1.25 mutations per megabase. RB1 and p53 mutations were identified in all five combined tumors. Combined tumors represent an immunophenotypically and genetically distinct variant of primary cutaneous neuroendocrine carcinomas, notable for a highly mutated genetic profile, significant p53 expression and/or mutation, absent RB1 expression in the context of increased RB1 mutation, and minimal neurofilament expression.

[Merkel cell carcinoma]

Merkel cell carcinoma is a rare aggressive malignant neuroendocrine skin tumor, which can metastasize to lymph nodes early and often shows local recurrence. The prognosis depends on tumor size and disease stage. The majority of recurrences appear during the first 2 years after the primary diagnosis. The 5-year survival rate for primary tumor < 2 cm is 66-75 % and for primary tumors > 2 cm is 50-60 %. With lymph node metastases the 5-year survival rate is 42-52 %, while with distant metastases it drops to 17-12 %. Extensive staging inclusive sentinel lymph node biopsy is essential to assess the risk for distant metastasis and to allow the best recommendations for therapy. After surgical treatment with adequate safety margin, subsequent adjuvant radiation therapy of the tumor region and lymphatic draining basin is recommended to reduce the risk of local recurrence and lymphatic spread.

Immunohistochemistry in dermatopathology

CONTEXT

Immunohistochemistry is not a diagnostic test but a highly valuable tool that requires interpretation within a context.

OBJECTIVE

To review the current status and limitations of immunohistochemistry in dermatopathology.

DATA SOURCES

English-language literature published between 1980 and 2014.

CONCLUSIONS

Although immunohistochemistry is rarely completely specific or sensitive, it is an important adjunctive technique in dermatopathology and can be helpful in a series of diagnostic dilemmas.

Diagnostic Immunohistochemistry in Cutaneous Neoplasia: An Update

Immunohistochemistry (IHC) is an important adjunct in the diagnosis of neoplastic skin diseases. In addition to the many established IHC markers currently in use, new markers continue to emerge, although their general acceptance and routine application requires robust validation. Here, we summarize the most well-established and commonly used biomarkers along with an array of newer ones reported in the past several decades that either demonstrate or hold high clinical promise in the field of cutaneous pathology. We also highlight recent applications of novel IHC markers in melanoma diagnosis including genetic mutation status markers [e.g. BRAF (v-raf murine sarcoma viral oncogene homolog B) and NRAS (neuroblastoma RAS viral oncogene homolog)] and an epigenetic alteration marker (e.g. 5-hydroxymethylcytosine). We specifically focus on the role of IHC in the differential diagnosis of cutaneous lesions that fall under the following categories: melanoma, epidermal tumors with an intraepidermal epitheliomatous pattern, spindle cell lesions of the dermis, small round blue cell tumors of the dermis, and cutaneous adnexal tumors. While IHC is a valuable tool in diagnostic dermatopathology, marker selection and interpretation must be highly informed by clinical context and the histologic differential diagnosis. With rapid progress in our understanding of the genetic and epigenetic mechanisms of tumorigenesis, new IHC markers will continue to emerge in the field of diagnostic dermatopathology.

Merkel cell carcinoma in the left groin: A case report and review of the literature

Merkel cell carcinoma (MCC) is a relatively rare but aggressive primary neuroendocrine carcinoma of the skin. MCC frequently occurs on sun-exposed areas in elderly Caucasian patients and has a propensity for local recurrence, regional lymph node invasion and distant metastases. However, MCC occurring on sites that are not sun-exposed in Asian patients is extremely uncommon. The current study describes the case of a 66-year-old Chinese male who presented with an asymptomatic, smooth lesion in the left inguinal region, which was initially diagnosed as a malignant lymphoma. Upon histological and immunohistochemical analysis, the tumor was consistent with the diagnosis of an MCC. In conclusion, due to its low incidence rate and lack of characteristic clinical manifestations, the final diagnosis of MCC relies on the analysis of histological findings and immunohistochemical markers following lesion biopsy or resection. The present study aimed to report a case of MCC and present a brief literature review in order to bring attention to the diagnosis of this condition.

Somatostatin Receptors 2A and 5 Are Expressed in Merkel Cell Carcinoma with No Association with Disease Severity

BACKGROUND/AIMS

Merkel cell carcinoma (MCC) is a rare high-grade neuroendocrine tumour of the skin. It has been speculated that MCCs express somatostatin receptors (SSTRs), but this has never been assessed in a large series of MCCs. The main aim of this study was to assess the expression of SSTR2A and SSTR5 in MCC tumours. The secondary aims were to assess whether expression of SSTR was associated with the Ki67 proliferative index, Merkel cell polyomavirus (MCPyV) status, clinical characteristics and outcome.

METHODS

Clinical data and tumours were collected from an ongoing cohort of French patients with MCC. Immunohistochemistry was performed with anti-SSTR2A and anti-SSTR5 monoclonal antibodies, and tumours were classified into 3 groups: 'no expression', 'low expression' and 'moderate expression' using an SSTR staining score.

RESULTS

SSTR expression was assessed for 105 MCC tissue samples from 98 patients, and clinical characteristics were available for 87 of them. SSTR expression was consistent between the primary skin tumour and the corresponding metastases for SSTR2A and SSTR5 in 3/7 and 6/7 cases, respectively. SSTR2A and SSTR5 were expressed in 58 cases (59.2%) and in 44 cases (44.9%), respectively. Overall, at least one SSTR was expressed in 75 tumours (76.5%). SSTR expression was not associated with clinical characteristics, Ki67 proliferative index, recurrence-free survival or MCC-specific survival. Expression of SSTR2A was associated with MCPyV status in MCC tumours but not SSTR5.

CONCLUSION

SSTRs were expressed in a high proportion of MCCs, although expression was heterogeneous between tumours and was not associated with disease severity.

Detection of mitotic figures and G2+ tumor nuclei with histone markers correlates with worse overall survival in patients with Merkel cell carcinoma

BACKGROUND

High mitotic figure count (MFC) correlates with low survival rate in Merkel cell carcinoma (MCC). However, the prognostic impact of histone biomarkers as surrogates of MFC in MCC is unknown. We evaluated the prognostic significance of the immunodetection of mitotic figures and of G2+ tumor nuclei with histone-associated mitotic markers H3K79me3T80ph (H3KT) and phosphohistone H3 (PHH3) in MCC.

METHODS

Immunohistochemical analyses of H3KT and PHH3 and proliferative marker Ki-67 were performed in a series of 21 cases of MCC. The significance of the pathologic data and immunoreactivity with these markers was evaluated with Pearson correlation and paired Student t-test. Univariate Cox proportional hazards regression models were performed to assess the relationships between these markers and survival.

RESULTS

H3KT detected a higher number of mitotic figure (p<0.0001) and G2+ tumor nuclei (p<0.0052) than did PHH3. Furthermore, the MFC combined with G2+ tumor nuclei detected with H3KT compared to PHH3 and manual MFC was a significant predictor of impaired survival in patients with MCC (p=0.035; HR=1.0172), corresponding to a 1.72% increased risk of death for each unit increase in H3KT.

CONCLUSIONS

Biomarker analysis of proliferative rates with histone markers may have relevance in stratifying risk in patients with MCC.

Mutational analysis of merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine malignancy that is associated with a poor prognosis. The pathogenesis of MCC is not well understood, and despite a recent plethora of mutational analyses, we have yet to find a set of signature mutations implicated in the majority of cases. Mutations, including TP53, Retinoblastoma and PIK3CA, have been documented in subsets of patients. Other mechanisms are also likely at play, including infection with the Merkel cell polyomavirus in a subset of patients, dysregulated immune surveillance, epigenetic alterations, aberrant protein expression, posttranslational modifications and microRNAs. In this review, we summarize what is known about MCC genetic mutations and chromosomal abnormalities, and their clinical significance. We also examine aberrant protein function and microRNA expression, and discuss the therapeutic and prognostic implications of these findings. Multiple clinical trials designed to selectively target overexpressed oncogenes in MCC are currently underway, though most are still in early phases. As we accumulate more molecular data on MCC, we will be better able to understand its pathogenic mechanisms, develop libraries of targeted therapies, and define molecular prognostic signatures to enhance our clinicopathologic knowledge.

Merkel cell carcinoma of lymph node with unknown primary has a significantly lower association with Merkel cell polyomavirus than its cutaneous counterpart

Rare cases of Merkel cell carcinoma have been encountered in lymph nodes with unknown extranodal primary, which exhibit similar morphologic and immunophenotypic features to those in primary cutaneous Merkel cell carcinomas. However, it is uncertain whether the nodal Merkel cell carcinoma is a primary tumor of the lymph node or represents a metastasis from an occult or regressed extranodal lesion. To establish an accurate diagnosis of the nodal Merkel cell carcinoma can be challenging because of significant morphologic mimics, including lymphoblastic lymphoma and metastatic small cell carcinoma. Moreover, there is no consensus for a diagnostic term, and many different terms have been used, which can be confusing and may not fully reflect the nature of nodal Merkel cell carcinoma. In this study, we investigated the detailed clinicopathologic features of 22 nodal Merkel cell carcinomas, with comparison to 763 primary cutaneous cases retrieved from the literature. Overall, the nodal and cutaneous Merkel cell carcinomas shared similar clinical presentations, morphologic spectrum, and immunophenotype; both were mostly seen in elderly male with a typical neuroendocrine morphology. Most of cases expressed CK20, synaptophysin, and chromogranin A; and PAX5 and TdT were also positive in majority of cases. However, nodal Merkel cell carcinomas had a significantly lower association with Merkel cell polyomavirus than cutaneous cases (31% vs 76%, P=0.001). Therefore, these two entities may arise from overlapping but not identical biological pathways. We also recommend the use of the diagnostic term 'Merkel cell carcinoma of lymph node' to replace many other names used.

Merkel cell carcinoma - recent advances in the biology, diagnostics and treatment

Merkel cell carcinoma (MCC) is an uncommon primary cutaneous carcinoma with neuroendocrine differentiation. Since recent discovery of MCCs strong association with Merkel cell polyomavirus (MCPyV), there has been a rapid increase in the understanding of the carcinomas genetics, molecular biology and pathogenesis. In our study, we reviewed recent advances and controversies concerning MCC histogenesis, epidemiology, diagnostic and prognostic markers. We analyzed the association of MCPyV with MCC and the possible new targets for therapy. We also examined English-based literature regarding MCC pathogenesis published between 2008 and 2013, which lead to a deeper understanding of the topic. Our study showed that the association of MCPyV strongly influences the course of MCC. Additionally, it has been shown that a immunological response to MCPyV may in the future give hope to identify new therapeutic strategies in treatment of this fatal malignancy. This article is part of a Directed Issue entitled: Rare Cancers.

Expression of β-catenin and cyclin D1 in Merkel cell carcinomas of the head and neck

BACKGROUND

Merkel cell carcinomas (MCC) are very aggressive tumors of the sun-exposed skin with a high potential to metastasize. Little is known about the genesis of MCC and very few prognostic markers have been detected so far. The Wnt pathway protein β-catenin and the cell cycle protein cyclin D1 are two promotors of tumor growth and are expressed in a variety of malignant neoplasms such as lymphomas, thyroid, breast cancer, and many others.

PATIENTS AND METHODS

Tissue samples of 27 patients with MCC were immunohistochemically stained for β-catenin and cyclin D1 and correlated with overall survival of patients. In addition, western blot analysis was carried out in the two MCC cell lines MCC-13 and MCC-26.

RESULTS

β-catenin showed a cytoplasmatic expression of 10-30 % in 11 samples and an expression lower than 10 % in eight samples. Nuclear staining was visible in two samples. None of the 27 samples expressed cyclin D1.

CONCLUSION

Neither cyclin D1 nor β-catenin was expressed in a statistically significant manner, concluding that the development of MCCs is independent of β-catenin and cyclin D1 expression and these proteins are not suitable as prognostic markers. We could describe the expression pattern of cyclin D1 for the first time.

A better prognosis for Merkel cell carcinoma of unknown primary origin

BACKGROUND

There is limited evidence that Merkel cell carcinoma (MCC) arising from a nodal basin without evidence of a primary cutaneous (PC) site has better prognosis. We present our experience at 2 tertiary care referral centers with stage III MCC with and without a PC site.

METHODS

Fifty stage III MCC patients were identified between 1996 and 2011. Clinical data were analyzed, with primary endpoints being disease-free survival and overall survival.

RESULTS

Of stage III patients, 34 patients presented with a PC site and 16 patients with an unknown primary (UP) site. Treatment strategies varied; of patients with UP vs. PC sites, 25% vs. 44% underwent combined regional lymphadenectomy and radiation, with an additional 25% vs. 15% receiving chemotherapy. The median disease-free survival for a UP site was not reached vs. 15 months for a PC site (hazards ratio = .48, P = .18). The median overall survival for a UP site was not reached vs 21 months for a PC site (hazards ratio = .34, P = .03). Multivariate analysis showed that UP status was a significant factor in overall survival (P = .002).

CONCLUSIONS

Stage III MCC with a UP site portends a better prognosis than MCC with a PC site.

Human Merkel cell polyomavirus: virological background and clinical implications

The Merkel cell polyomavirus (MCPyV), identified in humans in 2008, is associated with a relatively rare but aggressive neuroendocrine skin cancer, the Merkel cell carcinoma (MCC). MCC incidence is increasing due to the advancing age of the population, the increase in damaging sun exposure and in the number of immunocompromised individuals. MCPyV must be considered as the etiological agent of MCC and thus is the first example of a human oncogenic polyomavirus. MCPyV infection is common, and seroprevalence studies indicate that widespread exposure begins early in life. The majority of adults have anti-MCPyV antibodies and there is a growing body of evidence that healthy human skin harbors resident or transient MCPyV suggesting that MCPyV infection persists throughout life. However, the mode of transmission, the host cells, and the latency characteristics of this virus remain to be elucidated. In addition, it is still not clear whether MCPyV is associated with diseases or lesions other than Merkel cell carcinoma. The etiologic role of MCPyV in MCC opens up opportunities to improve the understanding of this cancer and to potentially improve its treatment.

Specific analysis of KIT and PDGFR-alpha expression and mutational status in Merkel cell carcinoma

BACKGROUND

The purpose of this study was to explore the immunohistochemical and mutational status of the tyrosine kinases KIT and platelet derived growth receptor-alpha (PDGFRA) in Merkel cell carcinoma (MCC). Specifically, we examined the mutated exons in gastrointestinal stromal cell tumors that may confer a treatment response to imatinib mesylate.

METHODS

We evaluated KIT and PDGFRA immunostaining in 23 examples of MCC utilizing laser capture microdissection to obtain pure samples of tumor genomic DNA from 18 of 23 examples of MCC. PCR amplification and sequencing of KIT exons 9, 11, 13 and 17, and PDGFRA exons 10, 12, 14 and 18 for mutations was performed.

RESULTS

Fifteen of 23 tumors (65%) demonstrated CD117 expression and 22 of 23 tumors (95%) demonstrated PDGFRA expression. A single heterozygous KIT exon 11 base change resulting in an E583K mutation was discovered in 12 of 18 (66%) examples of MCC. In addition, a single nucleotide polymorphism was detected in eight of 18 tumors (44%) in exon 18 of PDGFRA (codon 824; GTC > GTT).

CONCLUSIONS

We discovered a novel somatic KIT exon 11 E583K mutation in 66% of tumors. This mutation has been previously described in a human with piebaldism and appears to represent an inactivating mutation. Therefore, despite expression of CD117 and PDGFRA, the absence of activating mutations in these tyrosine kinases makes KIT and PDGFRA unlikely candidates of MCC oncogenesis.

Clinicopathologic features of primary Merkel cell carcinoma: a detailed descriptive analysis of a large contemporary cohort

BACKGROUND

Little uniformity exists in the clinical and histologic variables reported with primary Merkel cell carcinoma (MCC).

OBJECTIVE

To provide a rigorous descriptive analysis of a contemporary cohort and promote the prospective collection of detailed data on MCC for future outcome studies.

METHODS AND MATERIALS

A detailed descriptive analysis was performed for clinical and histologic features of 147 patients with 150 primary MCC tumors in a prospectively collected database from 2006 to 2010.

RESULTS

The majority (73.5%) of patients were at American Joint Committee on Cancer clinical stage I or II at presentation, 20.4% at stage III, and 6.1% at stage IV. Detailed descriptive clinical and histologic findings are presented.

CONCLUSION

Clinical and histologic profiling of primary MCC in the literature is variable and limited. Systematic prospective collection of MCC data is needed for future outcome studies and the ability to compare and share data from multiple sources for this relatively rare tumor.

The role of the immune response in merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine skin cancer. The Merkel cell polyomavirus (MCPyV) is implicated in its pathogenesis. Immune mechanisms are also implicated. Patients who are immunosuppressed have an increased risk. There is evidence that high intratumoral T-cell counts and immune transcripts are associated with favorable survival. Spontaneous regressions implicate immune effector mechanisms. Immunogenicity is also supported by observation of autoimmune paraneoplastic syndromes. Case reports suggest that immune modulation, including reduction of immune suppression, can result in tumor regression. The relationships between MCPyV infection, the immune response, and clinical outcome, however, remain poorly understood. Circulating antibodies against MCPyV antigens are present in most individuals. MCPyV-reactive T cells have been detected in both MCC patients and control subjects. High intratumoral T-cell counts are also associated with favorable survival in MCPyV-negative MCC. That the immune system plays a central role in preventing and controlling MCC is supported by several observations. MCCs often develop, however, despite the presence of humoral and cellular immune responses. A better understanding on how MCPyV and MCC evade the immune response will be necessary to develop effective immunotherapies.

Value of thyroid transcription factor-1 immunostaining in tumor diagnosis: a review and update

Thyroid transcription factor-1 (TTF-1) is a tissue-specific transcription factor that plays a critical role in the normal development of embryonic epithelial cells of the thyroid and lung. Because TTF-1 expression is highly restricted to epithelial tumors arising in these organs, it is, at present, one of the immunohistochemical markers most commonly used to assist in the differential diagnosis of carcinomas of the lung and thyroid. Recent studies, however, have reported that TTF-1 is not as specific for lung and thyroid carcinomas as was previously thought as it can be found to be expressed, although much less frequently, in some carcinomas arising in other organs, such as the ovaries, endometrium, colon, and breast, as well as in some tumors of the central nervous system. Even though this unexpected TTF-1 positivity has been reported more frequently with the recently available SPT24 anti-TTF-1 monoclonal antibody, it has also been shown to occur with the commonly used 8G7G3/1 clone, albeit in a lower percentage of cases. Despite these findings, TTF-1 remains a very useful immunohistochemical marker in diagnostic pathology.

[A probable etiological role of Merkel cell polyomavirus in the development of Merkel cell carcinoma]

Approximately 20% of the tumours in humans are associated with contagious viral agents. Merkel cell carcinoma is a rare and highly aggressive tumour which may originate from the epidermal stratum basale, although the origin is still controversial. This tumour is most commonly found in elderly and immunocompromised patients in sun exposed areas, especially in the head and neck regions. Merkel cell carcinoma often causes a diagnostic challenge with a dramatically increasing incidence. In 2008, a DNA tumour virus, a polyomavirus (Merkel cell polyomavirus) was detected in Merkel cell carcinomas, and this finding helped to understand the etiological background of the disease. The infectious - probably viral - etiology resulted in a paradigm shift in pathogenesis and, hopefully, in therapy as well. This review summarizes the current knowledge related to Merkel cell carcinoma and the first oncogenic human polyomavirus, the Merkel cell polyomavirus, to promote the clinical adaptation of the information.

Which are the cells of origin in merkel cell carcinoma?

Merkel cell carcinoma (MCC), a highly aggressive skin tumour with increasing incidence, is associated with the newly discovered Merkel cell polyomavirus (MCPyV). Studies on MCC and MCPyV as well as other risk factors have significantly increased our knowledge of MCC pathogenesis, but the cells of origin, which could be important targets in future therapies, are still unknown. Merkel cells (MCs), the neuroendocrine cells of the skin, were believed to be at the origin of MCC due to their phenotypic similarities. However, for several reasons, for example, heterogeneous differentiation of MCCs and postmitotic character of MCs, it is not very likely that MCC develops from differentiated MCs. Skin stem cells, probably from the epidermal lineage, are more likely to be cells of origin in MCC. Future studies will have to address these questions more directly in order to identify the physiological cells which are transformed to MCC cells.

Immunohistochemical endothelial markers: a review

A relatively large number of new endothelial markers that can assist in the diagnosis and classification of endothelial and vascular neoplasms have become available over the past few years. The expression of these markers, however, differs considerably among the various tumors. A selection of markers that have potential diagnostic utility or are of current interest among pathologists are reviewed and compared with some of the more traditional markers that have been employed in diagnostic pathology.

Increasing tumor thickness is associated with recurrence and poorer survival in patients with Merkel cell carcinoma

BACKGROUND

Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous neuroendocrine tumor usually occurring on sun-exposed skin in elderly patients. Clinical and pathologic factors associated with disease progression and mortality in patients with MCC are poorly defined. Recently, it has been reported that p63 expression in primary MCC is strongly associated with clinical outcome.

METHODS

MCC patients diagnosed between July 1, 1993 and July 31, 2009 were identified from the surgical pathology records of the Sydney South West Area Health Service. Clinical, pathologic, treatment, and survival data were obtained and immunohistochemical analyses for p53, p63, and Ki-67 were performed. The associations of clinical and pathologic features with disease-free and disease-specific survival were analyzed.

RESULTS

Ninety-five patients were identified (67 males, 28 females; median age at diagnosis of primary MCC 76 [range, 42-93] years). Increasing primary tumor thickness was significantly associated with poorer disease-free survival (5-year survival 18 % in tumors >10 mm thick compared with 69 % for patients with tumors ≤10 mm thick, p = 0.002) and disease-specific survival (5-year survival 74 % in tumors >10 mm thick compared with 97 % for patients with tumors ≤10 mm thick, p = 0.006). There was a strong positive correlation between the Ki-67 index (proportion of Ki-67-positive tumor nuclei) and tumor thickness (r = 0.39, n = 45, p = 0.008). Positive staining for p63 in MCC was infrequent (9 % of primary MCC) and showed no significant association with disease outcome.

CONCLUSIONS

Tumor thickness is significantly associated with disease-free survival in MCC. We recommend that primary tumor thickness be routinely recorded in the pathology reports of patients with primary MCC.

Tumor infiltrating immune cells and outcome of Merkel cell carcinoma: a population-based study

PURPOSE

Merkel cell carcinoma (MCC) is a rare skin cancer that often harbors Merkel cell polyomavirus (MCPyV) DNA. The clinical importance of intratumoral immune cells and their associations with MCPyV infection are poorly understood.

EXPERIMENTAL DESIGN

We identified T lymphocytes (CD3-positive cells), T-cell subsets (CD4, CD8, and FoxP3-positive cells), natural killer cells (small CD16-positive cells), and macrophages (CD68 and CD163-positive cells) in tumors of 116 individuals diagnosed with MCC in Finland from 1979 to 2004 using immunohistochemistry and detected MCPyV DNA with quantitative PCR. The associations between immune cell counts, MCPyV DNA, patient and tumor characteristics, and patient outcome were examined.

RESULTS

MCPyV DNA-positive cancers contained higher numbers of CD3(+), CD8(+), CD16(+), FoxP3(+), and CD68(+) cells as compared with MCPyV DNA-negative carcinomas (all P values < 0.05). High intratumoral numbers of CD3(+), CD8(+), or FoxP3(+) cells, and high CD8(+)/CD4(+) or FoxP3(+)/CD4(+) ratios, were significantly associated with favorable overall survival. Individuals with a high tumor CD3(+) count had metastases less often and survived longer, irrespective of the tumor MCPyV status. Tumor CD3(+) count and MCPyV DNA status had independent influence on survival in a Cox multivariable model that also included presence of locoregional metastases at diagnosis and gender as covariates.

CONCLUSIONS

High intratumoral T-lymphocyte counts are associated with favorable survival in MCC. Although the numbers of T cells are generally higher in MCPyV-positive than in MCPyV-negative MCC, high intratumoral T-cell counts are also associated with favorable survival in MCPyV-negative MCC.

Selective radiotherapy for the treatment of head and neck Merkel cell carcinoma

BACKGROUND

The role of radiotherapy (RT) in the management of Merkel cell carcinoma (MCC) is controversial. The authors of this report evaluated the rates and patterns of failure in a selected group of patients who underwent RT for MCC of the head and neck (HN).

METHODS

The records of 145 consecutive patients with MCC of the HN who presented to the authors' institution between 1988 and 2009 were reviewed. Only patients who received RT at the institution were included. The cumulative incidence of locoregional failure (LRF), distant metastatic failure (DMF), disease progression (DP) and disease-specific death (DSD) were estimated with death as a competing risk.

RESULTS

Forty-eight patients were identified. The median follow-up was 51 months (range, 6-220 months) for living patients. LRF developed in 5 patients (10%), and those patients had a median time to recurrence of 3 months. Two of the 5 LRFs were local and developed at the edge of the treatment field; the remaining 3 LRFs were in lymph nodes and occurred outside the treatment field. DMF developed in 12 patients (25%). The estimated 5-year cumulative incidences of LRF, DP, and DSD were 10%, 30%, and 21%, respectively. Acute toxicities included 5 episodes (10%) of grade 3 dermatitis and 1 episode (2%) of grade 3 mucositis.

CONCLUSIONS

The authors report a site-specific series of patients with HN MCC who received RT. In this group of patients with adverse features, RT was well tolerated, and LRF was low. The propensity for MCC to recur at the edge of the treatment field suggests that generous margins are appropriate when RT is administered.

Advances in Merkel cell carcinoma pathogenesis and management: a recently discovered virus, a new international consensus staging system and new diagnostic codes

Merkel cell carcinoma is a rare but aggressive neuroendocrine carcinoma of the skin with a rising incidence and a high mortality rate. It occurs primarily in sun-exposed skin of older individuals. It is characterized by a high rate of local recurrence, regional lymph node metastases and distant metastases, occurring even after prompt treatment. Many controversies exist regarding its pathogenesis and optimal management. The discovery of Merkel cell polyomavirus has been a major breakthrough in understanding the aetiology of the disease. A recently adopted new international consensus staging system in combination with new international diagnostic codes are expected to facilitate future clinical trials and improve the management of patients. According to recent (2010) guidelines, most patients should be managed with a combination of surgery and radiotherapy.

Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine carcinoma of the skin. The incidence of this rare tumor is increasing rapidly; the American Cancer Society estimates for 2008 almost 1500 new cases in the USA. Thus, the incidence of MCC will exceed the incidence of cutaneous T-cell lymphoma. Moreover, the mortality rate of MCC at 33% is considerably higher than that of cutaneous melanoma. These clinical observations are especially disturbing as we are only recently beginning to understand the pathogenesis of MCC. For the same reason, the therapeutic approach is often unclear; reliable data are only available for the therapy of locoregional disease.

[Merkel cell carcinoma revisited: a new example of viro-induced human tumour]

Merkel cell carcinoma (MCC) is a neuroendocrine carcinoma of the skin of poor outcome. A new type of virus, isolated in 2008, was found to be strongly associated with CCM. This virus, belonging to the family of polyomavirus, was called MCPyV for Merkel Carcinoma Polyomavirus. Recent data favour a causative role of MCPyV in oncogenesis. MCC represents thus a new model for the understanding of the mechanisms of oncogenesis. The distinct molecular viral signature in every case of MCC represents an original tool for the follow-up of the disease. New therapeutic perspectives are to be drawn using this model.

Merkel cell carcinoma - a population-based epidemiological study in Finland with a clinical series of 181 cases

BACKGROUND

Merkel cell carcinoma (MCC) is a rare malignancy of the skin, and its incidence is reported to be rising. The purpose of this study was to calculate its incidence and survival ratios, and to describe the clinical characteristics of Merkel cell carcinoma patients in Finland.

METHODS

We calculated the incidence of MCC based on data from the Finnish Cancer Registry. In addition, patient files from hospitals and primary health care centres were reviewed for detailed data on the treatment and disease recurrence of 181 patients diagnosed with MCC in Finland during 1983-2004, and relative survival ratios were calculated for them.

RESULTS

The incidence (per 100,000) of MCC in Finland in 1989-2008 was 0.11 for men and 0.12 for women, adjusted for age to the world standard population. The mean age at diagnosis was 76 years (range 27-100), and 69% of the patients were women. The most common site of the primary tumour was the head and neck (53%). No extra benefit was gained from a wide surgical margin (≥ 2 cm) compared to a margin of 0.1-0.19 cm, but an intralesional excision was more often associated with local recurrence. None of the patients with Stage I-II disease who had received postoperative radiotherapy to the tumour bed had a local recurrence. The 5-year relative survival ratio amongst men was 36% (95% confidence interval 20-54%), and amongst women 69% (56 to -82%).

CONCLUSIONS

MCC is a rare disease in Finland, with incidence rates similar to those in the other Nordic countries. Our results support the view that complete excision with clear margins and post operative radiotherapy decrease local recurrences.

Giant Merkel cell carcinoma of the eyelid: a case report and review of the literature

Merkel cell carcinoma (MCC) is a rare cutaneous tumor and cases located in the eyelid have been described, but still its rarity may lead to difficulty in diagnosis and delay in treatment. A 51-year-old female patient that presented with large lesions in the eyelid underwent surgery after the diagnosis of acute chalazion. Following respiratory distress secondary to pulmonary metastasis, the patient's condition deteriorated and was not fit for complete excision treatment. Histopathological investigation of the biopsies, taken from the tumor, revealed that it was undifferentiated small cell carcinoma. Our aim with this paper is to point out that more cases should be reported for more effective diagnosis, histopathological study, clinical investigation, treatment and prognosis of this specific neoplasm.

Features predicting sentinel lymph node positivity in Merkel cell carcinoma

PURPOSE

Merkel cell carcinoma (MCC) is a relatively rare, potentially aggressive cutaneous malignancy. We examined the clinical and histologic features of primary MCC that may correlate with the probability of a positive sentinel lymph node (SLN).

METHODS

Ninety-five patients with MCC who underwent SLN biopsy at the University of Michigan were identified. SLN biopsy was performed on 97 primary tumors, and an SLN was identified in 93 instances. These were reviewed for clinical and histologic features and associated SLN positivity. Univariate associations between these characteristics and a positive SLN were tested for by using either the χ(2) or the Fisher's exact test. A backward elimination algorithm was used to help create a best multiple variable model to explain a positive SLN.

RESULTS

SLN positivity was significantly associated with the clinical size of the lesion, greatest horizontal histologic dimension, tumor thickness, mitotic rate, and histologic growth pattern. Two competing multivariate models were generated to predict a positive SLN. The histologic growth pattern was present in both models and combined with either tumor thickness or mitotic rate.

CONCLUSION

Increasing clinical size, increasing tumor thickness, increasing mitotic rate, and infiltrative tumor growth pattern were significantly associated with a greater likelihood of a positive SLN. By using the growth pattern and tumor thickness model, no subgroup of patients was predicted to have a lower than 15% to 20% likelihood of a positive SLN. This suggests that all patients presenting with MCC without clinical evidence of regional lymph node disease should be considered for SLN biopsy.

Association of Merkel cell polyomavirus infection with morphologic differences in Merkel cell carcinoma

Recently, it has been shown that approximately 80% of Merkel cell carcinomas harbor a novel polyomavirus named Merkel cell polyomavirus, thought to be a carcinogenic agent. However, it is not fully elucidated whether Merkel cell carcinomas differ with regard to the presence or absence of Merkel cell polyomavirus. To address this, we investigated morphologic differences between Merkel cell polyomavirus-positive and -negative Merkel cell carcinomas by morphometry. Using polymerase chain reaction and real-time quantitative polymerase chain reaction, Merkel cell polyomavirus was detected in 20 (77%) of 26 Merkel cell carcinoma cases, including 4 Merkel cell carcinomas combined with squamous cell carcinomas. Interestingly, Merkel cell polyomavirus was detected only in ordinary (pure) Merkel cell carcinomas; none of the 4 combined Merkel cell carcinomas + squamous cell carcinomas was positive for Merkel cell polyomavirus (P = .001). Morphometric analyses revealed that Merkel cell polyomavirus-negative Merkel cell carcinomas had more irregular nuclei (P < .001) and more abundant cytoplasm (P = .001) than Merkel cell polyomavirus-positive Merkel cell carcinomas, which had uniform round nuclei and scant cytoplasm. Reliability of the morphometry was confirmed using intraobserver and interobserver reliability tests. These results demonstrated statistically significant differences in tumor cell morphology between Merkel cell polyomavirus-positive and -negative Merkel cell carcinomas and reconfirmed the absence of Merkel cell polyomavirus in combined tumors. Furthermore, the results strongly suggest fundamental biological differences between Merkel cell polyomavirus-positive and -negative Merkel cell carcinomas, supporting that Merkel cell polyomavirus plays an important role in the pathogenesis of Merkel cell polyomavirus-positive Merkel cell carcinoma.