Diagnostic accuracy of a panel of immunohistochemical and molecular markers to distinguish Merkel cell carcinoma from other neuroendocrine carcinomas

TTF-1 is a highly sensitive but not fully specific marker for pulmonary and thyroidal cancer: a tissue microarray study evaluating more than 17,000 tumors from 152 different tumor entities

Thyroid transcription factor 1 (TTF-1) immunohistochemistry (IHC) is routinely used for the distinction of primary pulmonary adenocarcinomas. However, TTF-1 can also occur in other malignancies. A tissue microarray containing 17,772 samples from 152 different tumor types was analyzed. Napsin-A, CK20, SATB2, FABP1, and Villin-1 IHC data were available from previous studies. TTF-1 staining was seen in 82 of 152 tumor categories including thyroidal cancers (19-100%), adenocarcinomas (94%), neuroendocrine tumors (67%) of the lung, small cell neuroendocrine carcinomas (71-80%), mesenchymal tumors (up to 42%), and thymomas (39%). Comparative analysis of TTF-1 and Napsin-A revealed a sensitivity/specificity of 94%/86% (TTF-1), 87%/98% (Napsin-A), and 85%/99.1% (TTF-1 and Napsin-A) for the distinction of pulmonary adenocarcinomas. Combined analysis of TTF-1 and enteric markers revealed a positivity for TTF-1 and at least one enteric marker in 22% of pulmonary adenocarcinomas but also a TTF-1 positivity in 6% of colorectal, 2% of pancreatic, and 3% of gastric adenocarcinomas. TTF-1 is a marker of high sensitivity but insufficient specificity for pulmonary adenocarcinomas. A small fraction of TTF-1-positive gastrointestinal adenocarcinomas represents a pitfall mimicking enteric-type pulmonary adenocarcinoma. Combined analysis of TTF-1 and Napsin-A improves the specificity of pulmonary adenocarcinoma diagnosis.

Wnt/β-Catenin-Activated Nonpilomatrical Carcinoma of the Skin: A Case Series

Among skin epithelial tumors, recurrent mutations in the APC/CTNNB1 genes resulting in activation of the Wnt/β-catenin pathway have been reported predominantly in neoplasms with matrical differentiation. In the present study, we describe the morphologic, immunohistochemical, and genetic features of 16 primary cutaneous carcinomas harboring mutations activating the Wnt/β-catenin pathway without evidence of matrical differentiation, as well as 4 combined tumors in which a similar Wnt/β-catenin-activated carcinoma component was associated with Merkel cell carcinoma (MCC) or pilomatrical carcinoma. Among the pure tumor cases, 6 of 16 patients were women with a median age of 80 years (range, 58-98 years). Tumors were located on the head and neck (n = 7, 44%), upper limb (n = 4, 25%), trunk (n = 3, 18%), and leg (n = 2, 13%). Metastatic spread was observed in 4 cases resulting in death from disease in 1 patient. Microscopically, all cases were poorly differentiated neoplasms infiltrating the dermis and/or subcutaneous tissue. In 13 cases, solid "squamoid" areas were associated with a basophilic component characterized by rosette/pseudoglandular formation resulting in a biphasic appearance. Three specimens consisted only of poorly differentiated carcinoma lacking rosette formation. Immunohistochemical studies showed frequent expression of EMA (100%), BerEP4 (100%), cytokeratin 7 (94%), chromogranin A (44%), synaptophysin (82%), and cytokeratin 20 (69%). Complete loss of Rb expression was observed in all but 1 case. Nuclear β-catenin and CDX2 expressions were detected in all cases. Recurrent pathogenic somatic mutations were observed in APC (60%), CTNNB1 (40%), and RB1 (n = 47%). Global methylation analysis confirmed that cases with rosette formation constituted a homogeneous tumor group distinct from established skin tumor entities (pilomatrical carcinoma, MCC, and squamous cell carcinoma), although the 3 other cases lacking such morphologic features did not. In addition, we identified 4 combined neoplasms in which there was a component showing a similar poorly differentiated rosette-forming carcinoma demonstrating Rb loss and β-catenin activation associated with either MCC (n = 3) or pilomatrical carcinoma (n = 1). In conclusion, we describe a distinctive neoplasm, for which we propose the term "Wnt/β-catenin-activated rosette-forming carcinoma," morphologically characterized by the association of rosette formation, squamous and/or neuroendocrine differentiation, diffuse CDX2 expression, Rb loss, and mutations in CTNNB1/APC genes.

Paraneoplastic Neurologic Syndromes Associated With Merkel Cell Carcinoma

BACKGROUND AND OBJECTIVES

To define the clinical and immunologic profile of patients with paraneoplastic neurologic syndromes (PNSs) associated with Merkel cell carcinoma (MCC).

METHODS

Retrospective analysis was conducted on patients with suspected MCC-related PNS assessed at the French Reference Center, and cases were identified by a systematic review of the literature (MEDLINE, Embase) following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

RESULTS

A total of 17 patients were identified in our center and 30 in the systematic review, resulting in an overall cohort of 47 patients. The median age was 65 years (range 41-90), and 30 of 46 (65%) were men. Lambert-Eaton myasthenic syndrome (LEMS) (14/47, 29%), rapidly progressive cerebellar syndrome (11/47, 23%), and encephalomyelitis (EM) (8/47, 17%) were the most common associated clinical phenotypes. The most frequently associated neural antibodies (Abs) were voltage-gated calcium channel (VGCC)-Abs (14/45, 31%), followed by Hu-Abs (8/45, 17%) and neurofilament (NF)-Abs (8/45, 17%). Patients with NF-Abs only exhibited CNS disorders (8/8, 100%) and often had antibodies against >1 NF subunit (6/8, 75%). At onset, 26 of 43 patients (60%) had no identifiable primary skin tumor but had lymph node metastasis; these patients were more frequently men (21/26, 80%, vs 7/17, 41%; p = 0.007), had more frequently VGCC-Abs (12/26, 46%, vs 2/17, 11%, p = 0.02) predominantly among those with LEMS, and presented reduced mortality than patients with a known primary tumor (5/25, 20%, vs 8/15, 53%; p = 0.02).

DISCUSSION

MCC-related PNSs present as a heterogeneous clinical spectrum including central and/or peripheral nervous system disorders such as LEMS, RCPS, and EM, mainly associated with VGCC-Abs, NF-Abs, and Hu-Abs. NF-Abs were only seen among patients with CNS disorders. At onset, the absence of a primary skin tumor but presence of lymph node metastasis is frequently observed, and this particular clinical presentation is linked to reduced mortality, highlighting distinctive clinical and immunologic features of MCC-related PNS.

Aberrant positivity for BCOR immunohistochemistry in merkel cell carcinoma - a potential diagnostic pitfall

BACKRGOUND

Merkel cell carcinoma (MCC) is a rare, aggressive primary cutaneous neuroendocrine carcinoma, frequently associated with clonal Merkel cell polyomavirus integration. MCC can pose significant diagnostic challenges due to its diverse clinical presentation and its broad histological differential diagnosis. Histologically, MCC presents as a small-round-blue cell neoplasm, where the differential diagnosis includes basal cell carcinoma, melanoma, hematologic malignancies, round cell sarcoma and metastatic small cell carcinoma of any site. We here report strong aberrant immunoreactivity for BCOR in MCC, a marker commonly used to identify round cell sarcomas and other neoplasms with BCOR alterations.

METHODS

Based on strong BCOR expression in three index cases of MCC, clinically mistaken as sarcoma, a retrospective analysis of three patient cohorts, comprising 31 MCC, 19 small cell lung carcinoma (SCLC) and 5 cases of neoplasms with molecularly confirmed BCOR alteration was conducted. Immunohistochemical staining intensity and localization for BCOR was semi-quantitatively analyzed.

RESULTS

Three cases, clinically and radiologically mimicking a sarcoma were analyzed in our soft tissue and bone pathology service. Histologically, the cases showed sheets of a small round blue cell neoplasm. A broad panel of immunohistochemistry was used for lineage classification. Positivity for synaptophysin, CK20 and Merkel cell polyoma virus large T-antigen lead to the diagnosis of a MCC. Interestingly, all cases showed strong positive nuclear staining for BCOR, which was included for the initial work-up with the clinical differential of a round cell sarcoma. We analyzed a larger retrospective MCC cohort and found aberrant weak to strong BCOR positivity (nuclear and/or cytoplasmic) in up to 90% of the cases. As a positive control, we compared the expression to a small group of BCOR-altered neoplasms. Furthermore, we investigated a cohort of SCLC as another neuroendocrine neoplasm and found in all cases a diffuse moderate to strong BCOR positivity.

CONCLUSIONS

This study demonstrates that neuroendocrine neoplasms, such as MCC and SCLC can express strong aberrant BCOR. This might represent a diagnostic challenge or pitfall, in particular when MCC is clinically mistaken as a soft tissue or a bone sarcoma.

POU4F3 Is a Sensitive and Specific Marker of Merkel Cell Carcinoma

Although of therapeutic importance, a single sensitive and specific immunostain to distinguish Merkel cell carcinoma (MCC) from mimics is not currently available. In addition, single tumor cells are difficult to detect in sentinel lymph node biopsy. Leveraging publicly available data sets of 9264 solid tumors and >600,000 single-cell transcriptomes, we identified POU4F3 to be a specific marker of MCC. Analyses of Pan-Cancer RNA bulk sequencing data of 24 tumor types from Tumor Cancer Genomic Atlas data sets as well as non-Tumor Cancer Genomic Atlas small cell lung carcinoma and MCC data sets confirmed POU4F3 specificity for MCC. Single-cell RNA-sequencing analyses also confirmed the lack of POU4F3 expression in lung small cell carcinoma as well as a variety of normal tissues. Nuclear POU4F3 immunohistochemical expression was noted in 98.7% of 153 MCCs and in only 1.7% of mimics (3 of 180 cases, including 95 small cell carcinomas, of which 55 were from lungs and the remainder from other sites). Three POU4F3-positive non-MCC cases were from lungs (2 cases) and vagina (1 case). All 153 tested MCC cases were negative for ASCL1, a key transcriptional regulator highly expressed in small cell lung carcinoma. NeuroD1 was seen in a subset of MCC cases (20.9%, 32/153). POU4F3 immunostain was performed on 29 sentinel lymph nodes, and strong POU4F3 nuclear expression facilitated the ease of metastasis detection, even single tumor cells. Our study built on prior works shows that POU4F3 is a sensitive and specific clinical marker of MCC.

Analyses of combined Merkel cell carcinomas with neuroblastic components suggests that loss of T antigen expression in Merkel cell carcinoma may result in cell cycle arrest and neuroblastic transdifferentiation

Merkel cell carcinoma (MCC) is an aggressive skin cancer frequently caused by genomic integration of the Merkel cell polyomavirus (MCPyV). MCPyV-negative cases often present as combined MCCs, which represent a distinctive subset of tumors characterized by association of an MCC with a second tumor component, mostly squamous cell carcinoma. Up to now, only exceptional cases of combined MCC with neuroblastic differentiation have been reported. Herein we describe two additional combined MCCs with neuroblastic differentiation and provide comprehensive morphologic, immunohistochemical, transcriptomic, genetic and epigenetic characterization of these tumors, which both arose in elderly men and appeared as an isolated inguinal adenopathy. Microscopic examination revealed biphasic tumors combining a poorly differentiated high-grade carcinoma with a poorly differentiated neuroblastic component lacking signs of proliferation. Immunohistochemical investigation revealed keratin 20 and MCPyV T antigen (TA) in the MCC parts, while neuroblastic differentiation was confirmed in the other component in both cases. A clonal relation of the two components can be deduced from 20 and 14 shared acquired point mutations detected by whole exome analysis in both combined tumors, respectively. Spatial transcriptomics demonstrated a lower expression of stem cell marker genes such as SOX2 and MCM2 in the neuroblastic component. Interestingly, although the neuroblastic part lacked TA expression, the same genomic MCPyV integration and the same large T-truncating mutations were observed in both tumor parts. Given that neuronal transdifferentiation upon TA repression has been reported for MCC cell lines, the most likely scenario for the two combined MCC/neuroblastic tumors is that neuroblastic transdifferentiation resulted from loss of TA expression in a subset of MCC cells. Indeed, DNA methylation profiling suggests an MCC-typical cellular origin for the combined MCC/neuroblastomas. © 2024 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Merkel cell carcinoma: updates in tumor biology, emerging therapies, and preclinical models

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine carcinoma thought to arise via either viral (Merkel cell polyomavirus) or ultraviolet-associated pathways. Surgery and radiotherapy have historically been mainstays of management, and immunotherapy has improved outcomes for advanced disease. However, there remains a lack of effective therapy for those patients who fail to respond to these established approaches, underscoring a critical need to better understand MCC biology for more effective prognosis and treatment. Here, we review the fundamental aspects of MCC biology and the recent advances which have had profound impact on management. The first genetically-engineered mouse models for MCC tumorigenesis provide opportunities to understand the potential MCC cell of origin and may prove useful for preclinical investigation of novel therapeutics. The MCC cell of origin debate has also been advanced by recent observations of MCC arising in association with a clonally related hair follicle tumor or squamous cell carcinoma in situ. These studies also suggested a role for epigenetics in the origin of MCC, highlighting a potential utility for this therapeutic avenue in MCC. These and other therapeutic targets form the basis for a wealth of ongoing clinical trials to improve MCC management. Here, we review these recent advances in the context of the existing literature and implications for future investigations.

DNA Damage Stress Control Is a Truncated Large T Antigen and Euchromatic Histone Lysine Methyltransferase 2-Dependent Central Feature of Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is an aggressive skin cancer with a high mortality rate. Merkel cell polyomavirus causes 80% of MCCs, encoding the viral oncogenes small T and truncated large T (tLT) antigens. These proteins impair the RB1-dependent G1/S checkpoint blockade and subvert the host cell epigenome to promote cancer. Whole-proteome analysis and proximal interactomics identified a tLT-dependent deregulation of DNA damage response (DDR). Our investigation revealed, to our knowledge, a previously unreported interaction between tLT and the histone methyltransferase EHMT2. T antigen knockdown reduced DDR protein levels and increased the levels of the DNA damage marker γH2Ax. EHMT2 normally promotes H3K9 methylation and DDR signaling. Given that inhibition of EHMT2 did not significantly change the MCC cell proteome, tLT-EHMT2 interaction could affect the DDR. With tLT, we report that EHMT2 gained DNA damage repair proximal interactors. EHMT2 inhibition rescued proliferation in MCC cells depleted for their T antigens, suggesting impaired DDR and/or lack of checkpoint efficiency. Combined tLT and EHMT2 inhibition led to altered DDR, evidenced by multiple signaling alterations. In this study, we show that tLT hijacks multiple components of the DNA damage machinery to enhance tolerance to DNA damage in MCC cells, which could explain the genetic stability of these cancers.

Merkel-cell carcinoma: ESMO-EURACAN Clinical Practice Guideline for diagnosis, treatment and follow-up

•This ESMO Clinical Practice Guideline provides key recommendations for managing Merkel-cell carcinoma (MCC). •Recommendations are based on available scientific data and the multidisciplinary group of experts’ collective opinion. •The guideline covers clinical and pathological diagnosis, staging and risk assessment, treatment and follow-up. •Algorithms for the management of locoregional and inoperable/metastatic disease are provided. •A multidisciplinary team with a high level of expertise in MCC should diagnose and make decisions about therapy.

SATB2, CKAE1/AE3, and synaptophysin as a sensitive immunohistochemical panel for the detection of lymph node metastases of Merkel cell carcinoma

Histopathological evaluation of lymph nodes in Merkel cell carcinoma has become crucial in progression estimation and treatment modification. This study was undertaken to determine the most sensitive immunohistochemical panel for detecting MCC nodal metastases. We included 56 patients with 102 metastatic MCC lymph nodes, which were tested with seven antibodies: cytokeratin (CKAE1/AE3), CK20, chromogranin A, synaptophysin, INSM1, SATB2, and neurofilament (NF). Tissue microarrays (TMA) composed of 2-mm tissue cores from each nodal metastasis were constructed. A semiquantitative 5-tier scoring system (0%, < 25%, 25-74%, 75-99%, 100% positive MCC cells with moderate to strong reactivity) was implemented. In the statistical assessment, we included Merkel cell polyomavirus (MCPyV) status and expression heterogeneity between lymph nodes from one patient. A cumulative percentage of moderate to strong expression ≥ 75% of tumoral cells was observed for single cell markers as follows: 91/102 (89.2%) SATB2, 85/102 (83%) CKAE1/AE3, 80/102 (78.4%) synaptophysin, 75/102 (75.5%) INSM1, 68/102 (66.7%) chromogranin A, 60/102 cases (58.8%) CK20, and 0/102 (0%) NF. Three markers presented a complete lack of immunoreactivity: 8/102 (7.8%) CK20, 7/102 (6.9%) chromogranin A, and 6/102 (5.9%) NF. All markers showed expression heterogeneity in lymph nodes from one patient; however, the most homogenous was INSM1. The probability of detecting nodal MCC metastases was the highest while using SATB2 as a first-line marker (89.2%) with subsequential adding CKAE1/AE3 (99%); these results were independent of MCPyV status. Synaptophysin showed a superior significance in confirming the neuroendocrine origin of metastatic cells. This comprehensive analysis allows us to recommend simultaneous evaluation of SATB2, CKAE1/AE3, and synaptophysin in the routine pathologic MCC lymph node protocol.

Imaging of Merkel cell carcinoma of the eyelid: A case report

Merkel cell carcinoma (MCC) is a rare primary neuroendocrine carcinoma commonly found in older adults in areas of the skin that are susceptible to ultraviolet ray damage. The current study reports the case of a 79-year-old woman who presented to the Affiliated Hospital of Zunyi Medical University (Zunyi, China) with a painless lump in the lower eyelid of the left eye accompanied by photophobic tears for 4 months. Head computed tomography (CT) and magnetic resonance imaging (MRI) showed a space-occupying lesion ~2.8×2.4 cm in size outside the left orbital muscle cone, which was poorly demarcated from the surrounding normal tissues. Markedly intense and tortuous walking vascular shadows were observed within the tumor tissues. Fluorine-18-fluorodeoxyglucose positron emission tomography (18F-FDG PET)/CT revealed increased 18F-FDG uptake in the corresponding lesions. Based on these imaging features, a malignant tumor was suspected. The patient subsequently underwent surgery. Postoperative pathology and immunohistochemistry revealed MCC. The clinical presentation of MCC is usually a painless soft-tissue nodule or mass that grows rapidly over a short period and is flesh-colored, bluish red or purple. A slightly hyperdense mass on CT, with equal T1-weighted and slightly longer T2-weighted MRI signals, and mild enhancement on contrast-enhanced scans, accompanied by significantly enhanced distorted vascular shadows and increased 18F-FDG uptake on PET/CT, are valuable in the diagnosis of eyelid MCC.

Detection of wildtype Merkel cell polyomavirus genomic sequence and VP1 transcription in a subset of Merkel cell carcinoma

AIMS

Merkel cell carcinoma (MCC) is frequently caused by the Merkel cell polyomavirus (MCPyV). Characteristic for these virus-positive (VP) MCC is MCPyV integration into the host genome and truncation of the viral oncogene Large T antigen (LT), with full-length LT expression considered as incompatible with MCC growth. Genetic analysis of a VP-MCC/trichoblastoma combined tumour demonstrated that virus-driven MCC can arise from an epithelial cell. Here we describe two further cases of VP-MCC combined with an adnexal tumour, i.e. one trichoblastoma and one poroma.

METHODS AND RESULTS

Whole-genome sequencing of MCC/trichoblastoma again provided evidence of a trichoblastoma-derived MCC. Although an MCC-typical LT-truncating mutation was detected, we could not determine an integration site and we additionally detected a wildtype sequence encoding full-length LT. Similarly, Sanger sequencing of the combined MCC/poroma revealed coding sequences for both truncated and full-length LT. Moreover, in situ RNA hybridization demonstrated expression of a late region mRNA encoding the viral capsid protein VP1 in both combined as well as in a few cases of pure MCC.

CONCLUSION

The data presented here suggest the presence of wildtype MCPyV genomes and VP1 transcription in a subset of MCC.

Merkel Cell Polyomavirus T Antigen-Mediated Reprogramming in Adult Merkel Cell Progenitors

Whether Merkel cells regenerate in adult skin and from which progenitor cells they regenerate are a subject of debate. Understanding Merkel cell regeneration is of interest to the study of Merkel cell carcinoma, a rare neuroendocrine skin cancer hypothesized to originate in a Merkel cell progenitor transformed by Merkel cell polyomavirus small and large T antigens. We sought to understand what the adult Merkel cell progenitors are and whether they can give rise to Merkel cell carcinoma. We used lineage tracing to identify SOX9-expressing cells (SOX9+ cells) as Merkel cell progenitors in postnatal murine skin. Merkel cell regeneration from SOX9+ progenitors occurs rarely in mature skin unless in response to minor mechanical injury. Merkel cell polyomavirus small T antigen and functional imitation of large T antigen in SOX9+ cells enforced neuroendocrine and Merkel cell lineage reprogramming in a subset of cells. These results identify SOX9+ cells as postnatal Merkel cell progenitors that can be reprogrammed by Merkel cell polyomavirus T antigens to express neuroendocrine markers.

A review of Merkel cell carcinoma

ABSTRACT

Merkel cell carcinoma (MCC) is a rare and aggressive type of metastatic, nonmelanoma skin cancer derived from Merkel cells in the epidermis. MCC can be induced by sun exposure or via Merkel cell polyomavirus (MCV) gene expression. MCV is found in most patients with MCC and is associated with a lower recurrence rate of MCC. MCC has a wide range of clinical presentations that make diagnosis challenging. Histologic examination is performed using unique markers to differentiate it from other diagnoses. This article reviews the pathogenesis, clinical presentation, histopathology, differential diagnosis, and treatment of MCC.

Merkel cell carcinoma: an update

Merkel cell carcinoma (MCC) is an uncommon primary cutaneous neuroendocrine carcinoma associated with an adverse prognosis. In recent years, our understanding of MCC biology has markedly progressed. Since the discovery of the Merkel cell polyomavirus, it has become clear that MCC represents an ontogenetically dichotomous group of neoplasms with overlapping histopathology. Specifically, most MCCs arise secondary to viral oncogenesis, while a smaller subset is the direct result of UV-associated mutations. The distinction of these groups bears relevance in their immunohistochemical and molecular characterization, as well as in disease prognosis. Further recent developments relate to the landmark utilization of immunotherapeutics in MCC, providing optimistic options for the management of this aggressive disease. In this review, we discuss both fundamental and emerging concepts in MCC, with a particular focus on topics of practical relevance to the surgical or dermatopathologist.

Distinct Regulation of EZH2 and its Repressive H3K27me3 Mark in Polyomavirus-Positive and -Negative Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is an aggressive skin cancer for which Merkel cell polyomavirus integration and expression of viral oncogenes small T and Large T have been identified as major oncogenic determinants. Recently, a component of the PRC2 complex, the histone methyltransferase enhancer of zeste homolog 2 (EZH2) that induces H3K27 trimethylation as a repressive mark has been proposed as a potential therapeutic target in MCC. Because divergent results have been reported for the levels of EZH2 and trimethylation of lysine 27 on histone 3, we analyzed these factors in a large MCC cohort to identify the molecular determinants of EZH2 activity in MCC and to establish MCC cell lines' sensitivity to EZH2 inhibitors. Immunohistochemical expression of EZH2 was observed in 92% of MCC tumors (156 of 170), with higher expression levels in virus-positive than virus-negative tumors (P = 0.026). For the latter, we showed overexpression of EZHIP, a negative regulator of the PRC2 complex. In vitro, ectopic expression of the large T antigen in fibroblasts led to the induction of EZH2 expression, whereas the knockdown of T antigens in MCC cell lines resulted in decreased EZH2 expression. EZH2 inhibition led to selective cytotoxicity on virus-positive MCC cell lines. This study highlights the distinct mechanisms of EZH2 induction between virus-negative and -positive MCC.

Updates in histopathological classification and tissue biomarkers of digestive neuroendocrine neoplasms: What the clinician should know

Histopathological classifications of neuroendocrine neoplasms (NEN) change regularly and the latest WHO classification published in 2022, which concerns all NEN in the body, attempts to standardize classifications in the different locations. Differentiation and proliferation mainly assessed by Ki-67 index are still the cornerstone of those classifications. However, many markers are now used for diagnostic (to check neuroendocrine differentiation, to identify the site of origin of a metastasis, to help separating high-grade neuroendocrine tumors/NET and neuroendocrine carcinoma/NEC), prognostic or theranostic purposes. NENs are often heterogeneous and this can lead to difficulties in classifications, biomarker and prognostic assessment. These different points are discussed successively in this review, insisting especially on the frequent digestive, gastro-entero-pancreatic (GEP) localizations.

Detection of Merkel Cell Polyomavirus (MCPyV) DNA and Transcripts in Merkel Cell Carcinoma (MCC)

Merkel cell polyomavirus (MCPyV) is the etiological agent of the majority of Merkel cell carcinoma (MCC): a rare skin tumor. To improve our understanding of the role of MCPyV in MCCs, the detection and analysis of MCPyV DNA and transcripts were performed on primary tumors and regional lymph nodes from two MCC patients: one metastatic and one non-metastatic. MCPyV-DNA was searched by a quantitative polymerase chain reaction (qPCR), followed by the amplification of a Large T Antigen (LTAg), Viral Protein 1 (VP1) and Non-Coding Control Region (NCCR). LTAg and VP1 transcripts were investigated by reverse-transcription PCR (RT-PCR). Viral integration was also studied, and full-length LTAg sequencing was performed. qPCR revealed that the primary tumor of both patients and the lymph node of one patient was positive for the small t-antigen, with an average value of 7.0 × 10² copies/µg. The same samples harbored LTAg, NCCR and VP1 DNA. Sequencing results showed truncated LTAg with the conserved retinoblastoma (Rb) protein binding motif and VP1 and NCCR sequences identical to the MCC350 strain. RT-PCR detected LTAg but not VP1 transcripts. The MCPyV genome was integrated into the primary tumor of both patients. The results confirmed the connection between MCPyV and MCC, assuming integration, LTAg truncation and Rb sequestration as key players in MCPyV-mediated oncogenesis.

S2k Guideline - Merkel cell carcinoma (MCC, neuroendocrine carcinoma of the skin) - Update 2022

Merkel cell carcinoma (MCC, ICD-O M8247/3) is a rare, malignant, primary skin tumor with epithelial and neuroendocrine differentiation. The tumor cells share many morphologic, immunohistochemical, and ultrastructural features with cutaneous Merkel cells. Nevertheless, the cell of origin of MCC is unclear. MCC appears clinically as a reddish to purple spherical tumor with a smooth, shiny surface and a soft to turgid, elastic consistency, usually showing rapid growth. Spontaneous and often complete regressions of the tumor are observed. These likely immunologically-mediated regressions explain the cases in which only lymph node or distant metastases are found at the time of initial diagnosis and why the tumor responds very well to immunomodulatory therapies even at advanced stages. Due to its aggressiveness, the usually given indication for sentinel lymph node biopsy, the indication of adjuvant therapies to be evaluated, as well as the complexity of the necessary diagnostics, clinical management should already be determined by an interdisciplinary tumor board at the time of initial diagnosis.

Dataset for the Reporting of Merkel Cell Carcinoma: Recommendations From the International Collaboration on Cancer Reporting (ICCR)

Accurate and complete pathology reports are critical for the optimal management of cancer patients. Protocols for the pathologic reporting of Merkel cell carcinoma (MCC) have been developed independently by the Royal College of Pathologists (UK) and the College of American Pathologists. In this study, data elements for pathologic reporting of MCC were analyzed by an international panel of pathologists and clinicians with the aim of developing a common, internationally agreed upon dataset useful for clinical practice. The International Collaboration on Cancer Reporting expert review panel developed a protocol containing "core" (required) and "noncore" (recommended) elements. Core elements were defined as those that had evidentiary support and were unanimously agreed upon by the review panel as essential for the clinical management, staging, and/or assessment of prognosis in patients with MCC. Noncore elements were those considered to be clinical of interest, but with lesser degrees of supportive evidence or nonactionable implications. Ten core data elements for pathology reports on primary MCC were defined. Development and agreement on this evidence-based protocol at an international level was accomplished in a timely and efficient manner. The template developed for melanoma reporting was used as a structural base for this initiative. It is applicable to, and may facilitate the development of, protocols for other tumor types. Widespread utilization of an internationally agreed upon structured pathology dataset for MCC can be expected to lead to improved patient management. It should also facilitate collaborative clinical research.

Glypican-3 (GPC3) is associated with MCPyV-negative status and impaired outcome in Merkel cell carcinoma

Introduction: Merkel cell carcinoma (MCC) is an aggressive skin cancer, related to the Merkel Cell Polyomavirus (MCPyV) in 80% of cases. Immune checkpoint inhibitors provide sustained benefit in about 50% of MCC patients with advanced disease. Glypican-3 (GPC3) is an oncofetal tumor antigen that is an attractive target for chimeric antigen receptor T cell therapy due to its highly restricted expression on normal tissue and high prevalence in several solid tumors. GPC3 is known to be expressed in MCC but its association with tumor characteristics or prognosis has not been reported. We investigated MCC GPC3 expression by immunohistochemistry (IHC) and its association with tumor characteristics, MCPyV status, and patient outcome.

Methods: The GC33 antibody clone was validated for GPC3 IHC staining of tumor specimens in comparison to an established GPC3 IHC antibody. An MCC tissue microarray was stained for GPC3 by IHC using GC33 antibody. Association of GPC3+ IHC with baseline characteristics, MCPyV status (qPCR) and outcome (death from MCC/recurrence) were assessed.

Results: Forty-two of 62 samples (67.7%) were GPC3+. GPC3 expression was more frequently observed in females (p = 0.048) and MCPyV-negative tumors (p = 0.021). By multivariate analysis, GPC3 expression was associated with increased death from disease (CSS) (hazard ratio [HR] 4.05, 95% CI 1.06–15.43), together with advanced age (HR 4.85, 95% CI 1.39–16.9) and male gender (HR 4.64, 95% CI 1.31–16.41).

Conclusions: GPC3 expression is frequent in MCC tumors, especially MCPyV-negative cases, and is associated with increased risk of death. High prevalence of surface GPC3 makes it a putative drug target.

Merkel Cell Carcinoma of the Upper Eye Lid with Atypical Clinical Appearance

Merkel cell carcinoma (MCC) is a rare aggressive neuroendocrine skin tumor that occurs mainly in the sun-exposed head and neck region, but rarely in the eyelid region. Early lymphogenic spread often leads to locoregional metastases, which is why early diagnosis is crucial. Classically, periocular MCC presents as a reddish-livid nodule in elderly patients, a visual diagnosis. However, given its low incidence and variable appearance, diagnosis can also be challenging. In both cases presented here, the MCC presented as a skin-colored swelling. In patient 1, the tumor showed a partially deep subaponeurotic localization and mimicked a B-cell lymphoma histopathologically, whereas in patient 2 it imitated a diffuse chalazion clinically. After immunohistochemical characterization and exclusion of metastases, the initial clinically benign appearing lesions in both patients were classified as CK20 negative MCC. The extensive upper eyelid defects were reconstructed by Cutler-Beard plastic surgery, a particular challenge in patient 1 given the oculus unicus situation. Our two cases demonstrate that Merkel cell carcinomas not only manifest as deep red cherry-shaped tumors, but can be skin-colored and mimic benign changes when atypical in location or infiltration pattern.

Diagnosis and treatment of Merkel cell carcinoma: European consensus-based interdisciplinary guideline - Update 2022

Merkel cell carcinoma (MCC) is a rare skin cancer, accounting for less than 1% of all cutaneous malignancies. It is found predominantly in white populations and risk factors include advanced age, ultraviolet exposure, male sex, immunosuppression, such as AIDS/HIV infection, haematological malignancies or solid organ transplantation, and Merkel cell polyomavirus infection. MCC is an aggressive tumour with 26% of cases presenting lymph node involvement at diagnosis and 8% with distant metastases. Five-year overall survival rates range between 48% and 63%. Two subsets of MCC have been characterised with distinct molecular pathogenetic pathways: ultraviolet-induced MCC versus virus-positive MCC, which carries a better prognosis. In both subtypes, there are alterations in the retinoblastoma protein and p53 gene structure and function. MCC typically manifests as a red nodule or plaque with fast growth, most commonly on sun exposed areas. Histopathology (small-cell neuroendocrine appearance) and immunohistochemistry (CK20 positivity and TTF-1 negativity) confirm the diagnosis. The current staging systems are the American Joint Committee on Cancer/Union for international Cancer control 8th edition. Baseline whole body imaging is encouraged to rule out regional and distant metastasis. For localised MCC, first-line treatment is surgical excision with postoperative margin assessment followed by adjuvant radiation therapy (RT). Sentinel lymph node biopsy is recommended in all patients with MCC without clinically detectable lymph nodes or distant metastasis. Adjuvant RT alone, eventually combined with complete lymph nodes dissection is proposed in case of micrometastatic nodal involvement. In case of macroscopic nodal involvement, the standard of care is complete lymph nodes dissection potentially followed by post-operative RT. Immunotherapy with anti-PD-(L)1 antibodies should be offered as first-line systemic treatment in advanced MCC. Chemotherapy can be used when patients fail to respond or are intolerant for anti-PD-(L)1 immunotherapy or clinical trials.

Merkel cell polyomavirus and associated Merkel cell carcinoma

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

Transcription Factor Expression in Sinonasal Neuroendocrine Neoplasms and Olfactory Neuroblastoma (ONB): Hyams' Grades 1-3 ONBs Expand the Spectrum of SATB2 and GATA3-Positive Neoplasms

Sinonasal neuroendocrine neoplasms (SN-NENs) are rare and mostly include neuroendocrine carcinoma (NEC), whereas neuroendocrine tumor (NET) is exceptional in this site. Olfactory neuroblastoma (ONB) is a malignant neuroectodermal neoplasm arising in the nasal cavity. Albeit crucial for correct patients' management, the distinction of high grade ONB from NEC is challenging and requires additional diagnostic markers. The transcription factor SATB2 has been recently introduced in routine diagnostics as an immunohistochemical marker of distal intestine differentiation. No specific data are available about SATB2 and GATA3 expression in SN-NENs. GATA3, SATB2, and, for comparison, CDX2 expression were investigated in a series of epithelial and non-epithelial SN-NENs. We collected 26 cases of ONB and 7 cases of epithelial SN-NENs diagnosed and treated in our Institution. ONBs were graded according to Hyams' system and epithelial NENs were reclassified into 5 NECs, 1 MiNEN, and 1 amphicrine carcinoma. Immunohistochemistry was performed using standard automated protocols. Hyams' grades 1-3 ONBs stained diffusely and intensely for SATB2, whereas grade 4 ONBs and NECs were globally negative. The non-neuroendocrine component of MiNEN and the amphicrine carcinoma were strongly positive. GATA3 was heterogeneously and unpredictably expressed in Hyams' grades 1-3 ONBs, whereas grade 4 ONBs and NECs were completely negative. CDX2 was negative in all cases. Our study identifies, for the first time, SATB2 and GATA3 expression as features of Hyams' grades 1-3 ONBs, expands the spectrum of SATB2 and GATA3-positive neoplasms, and suggests that Hyams' grade 4 ONBs are not only clinically but also biologically different from low graded ONBs.

Investigation of the RB1-SOX2 axis constitutes a tool for viral status determination and diagnosis in Merkel cell carcinoma

MCC (Merkel cell carcinoma) is an aggressive neuroendocrine cutaneous neoplasm. Integration of the Merkel cell polyomavirus (MCPyV) is observed in about 80% of the cases, while the remaining 20% are related to UV exposure. Both MCPyV-positive and -negative MCCs-albeit by different mechanisms-are associated with RB1 inactivation leading to overexpression of SOX2, a major contributor to MCC biology. Moreover, although controversial, loss of RB1 expression seems to be restricted to MCPyV-negative cases.The aim of the present study was to assess the performances of RB1 loss and SOX2 expression detected by immunohistochemistry to determine MCPyV status and to diagnose MCC, respectively.Overall, 196 MCC tumors, 233 non-neuroendocrine skin neoplasms and 70 extra-cutaneous neuroendocrine carcinomas (NEC) were included. SOX2 and RB1 expressions were assessed by immunohistochemistry in a tissue micro-array. Diagnostic performances were determined using the likelihood ratio (LHR).RB1 expression loss was evidenced in 27% of the MCC cases, 12% of non-neuroendocrine skin tumors and 63% of extra-cutaneous NEC. Importantly, among MCC cases, RB1 loss was detected in all MCPyV(-) MCCs, while MCPyV( +) cases were consistently RB1-positive (p < 0.001). SOX2 diffuse expression was observed in 92% of the MCC cases and almost never observed in non-neuroendocrine skin epithelial neoplasms (2%, p < 0.0001, LHR +  = 59). Furthermore, SOX2 diffuse staining was more frequently observed in MCCs than in extra-cutaneous NECs (30%, p < 0.001, LHR +  = 3.1).These results confirm RB1 as a robust predictor of MCC viral status and further suggest SOX2 to be a relevant diagnostic marker of MCC.

An update on the development of concepts, diagnostic criteria, and challenging issues for neuroendocrine neoplasms across different digestive organs

Digestive neuroendocrine neoplasms (NENs) are a group of heterogeneous neoplasms found throughout the digestive tract, with different behaviour and genetic background. In the last few years, nomenclature and WHO/UICC classifications of digestive NENs have changed, and molecular classifications have emerged, especially in pancreatic locations. Increasing patho-molecular details are needed to diagnose the different categories of NEN, including the use of helpful immunohistochemical markers. In this review, we address these topics in three successive chapters. We first briefly review recent updates in classifications, discuss important grading and proliferating issues and advances in the molecular understanding of NEN. Then, we provide an update on diagnosis, including the most important differential diagnoses of NEN, with a focus on high-grade neoplasms and mixed tumours. Finally, we highlight a variety of currently used and next-generation predictive and prognostic biomarkers as well as biomarkers of tumour origin and describe some site specificities of gastrointestinal NEN. We specifically focus on biomarkers available to pathologists with the potential to change the way patients with NEN are diagnosed and treated.

Update from the 5th Edition of the World Health Organization Classification of Head and Neck Tumors: Overview of the 2022 WHO Classification of Head and Neck Neuroendocrine Neoplasms

This review article provides a brief overview of the new WHO classification by adopting a question-answer model to highlight the spectrum of head and neck neuroendocrine neoplasms which includes epithelial neuroendocrine neoplasms (neuroendocrine tumors and neuroendocrine carcinomas) arising from upper aerodigestive tract and salivary glands, and special neuroendocrine neoplasms including middle ear neuroendocrine tumors (MeNET), ectopic or invasive pituitary neuroendocrine tumors (PitNET; formerly known as pituitary adenoma) and Merkel cell carcinoma as well as non-epithelial neuroendocrine neoplasms (paragangliomas). The new WHO classification follows the IARC/WHO nomenclature framework and restricts the diagnostic term of neuroendocrine carcinoma to poorly differentiated epithelial neuroendocrine neoplasms. In this classification, well-differentiated epithelial neuroendocrine neoplasms are termed as neuroendocrine tumors (NET), and are graded as G1 NET (no necrosis and < 2 mitoses per 2 mm²; Ki67 < 20%), G2 NET (necrosis or 2-10 mitoses per 2 mm², and Ki67 < 20%) and G3 NET (> 10 mitoses per 2 mm² or Ki67 > 20%, and absence of poorly differentiated cytomorphology). Neuroendocrine carcinomas (> 10 mitoses per 2 mm², Ki67 > 20%, and often associated with a Ki67 > 55%) are further subtyped based on cytomorphological characteristics as small cell and large cell neuroendocrine carcinomas. Unlike neuroendocrine carcinomas, head and neck NETs typically show no aberrant p53 expression or loss of RB reactivity. Ectopic or invasive PitNETs are subtyped using pituitary transcription factors (PIT1, TPIT, SF1, GATA3, ER-alpha), hormones and keratins (e.g., CAM5.2). The new classification emphasizes a strict correlation of morphology and immunohistochemical findings in the accurate diagnosis of neuroendocrine neoplasms. A particular emphasis on the role of biomarkers in the confirmation of the neuroendocrine nature of a neoplasm and in the distinction of various neuroendocrine neoplasms is provided by reviewing ancillary tools that are available to pathologists in the diagnostic workup of head and neck neuroendocrine neoplasms. Furthermore, the role of molecular immunohistochemistry in the diagnostic workup of head and neck paragangliomas is discussed. The unmet needs in the field of head and neck neuroendocrine neoplasms are also discussed in this article. The new WHO classification is an important step forward to ensure accurate diagnosis that will also form the basis of ongoing research in this field.

Overview of the 2022 WHO Classification of Neuroendocrine Neoplasms

In this review, we detail the changes and the relevant features that are applied to neuroendocrine neoplasms (NENs) in the 2022 WHO Classification of Endocrine and Neuroendocrine Tumors. Using a question-and-answer approach, we discuss the consolidation of the nomenclature that distinguishes neuronal paragangliomas from epithelial neoplasms, which are divided into well-differentiated neuroendocrine tumors (NETs) and poorly differentiated neuroendocrine carcinomas (NECs). The criteria for these distinctions based on differentiation are outlined. NETs are generally (but not always) graded as G1, G2, and G3 based on proliferation, whereas NECs are by definition high grade; the importance of Ki67 as a tool for classification and grading is emphasized. The clinical relevance of proper classification is explained, and the importance of hormonal function is examined, including eutopic and ectopic hormone production. The tools available to pathologists for accurate classification include the conventional biomarkers of neuroendocrine lineage and differentiation, INSM1, synaptophysin, chromogranins, and somatostatin receptors (SSTRs), but also include transcription factors that can identify the site of origin of a metastatic lesion of unknown primary site, as well as hormones, enzymes, and keratins that play a role in functional and structural correlation. The recognition of highly proliferative, well-differentiated NETs has resulted in the need for biomarkers that can distinguish these G3 NETs from NECs, including stains to determine expression of SSTRs and those that can indicate the unique molecular pathogenetic alterations that underlie the distinction, for example, global loss of RB and aberrant p53 in pancreatic NECs compared with loss of ATRX, DAXX, and menin in pancreatic NETs. Other differential diagnoses are discussed with recommendations for biomarkers that can assist in correct classification, including the distinctions between epithelial and non-epithelial NENs that have allowed reclassification of epithelial NETs in the spine, in the duodenum, and in the middle ear; the first two may be composite tumors with neuronal and glial elements, and as this feature is integral to the duodenal lesion, it is now classified as composite gangliocytoma/neuroma and neuroendocrine tumor (CoGNET). The many other aspects of differential diagnosis are detailed with recommendations for biomarkers that can distinguish NENs from non-neuroendocrine lesions that can mimic their morphology. The concepts of mixed neuroendocrine and non-neuroendocrine (MiNEN) and amphicrine tumors are clarified with information about how to approach such lesions in routine practice. Theranostic biomarkers that assist patient management are reviewed. Given the significant proportion of NENs that are associated with germline mutations that predispose to this disease, we explain the role of the pathologist in identifying precursor lesions and applying molecular immunohistochemistry to guide genetic testing.

SATB2 is expressed in neuroendocrine carcinoma of the uterine cervix

Neuroendocrine carcinoma (NEC) of the uterine cervix is less characterized than neuroendocrine neoplasms of other sites such as of the digestive system and the lung. Special AT-rich sequence-binding protein 2 (SATB2) recently emerged as a marker of well-differentiated neuroendocrine tumors of the lower gastrointestinal (GI) tract. Among NECs, SATB2 is more frequently expressed in cutaneous Merkel cell carcinoma than in NEC of other anatomical sites. In our study, we performed an immunohistochemical study of SATB2 in 16 NECs of the uterine cervix, where the expression of these markers is still undefined. SATB2 was expressed in 12/16 cervical NECs (75%), with 7/16 cases (44%) showing SATB2 positivity in ≥ 50% of cells. In 7 cervical NECs associated with a non-neuroendocrine component, the expression of SATB2 was restricted to the neuroendocrine component. SATB2 was positive in all cases that expressed CDX2 (n = 7) and TTF1 (n = 5), with no evident association with p16 and p53. Our study demonstrated that SATB2 is often expressed in NECs of the uterine cervix. This information should be taken into account when assessing the origin of a NEC.

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

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

Merkel Cell Carcinoma: An Immunotherapy Fairy-Tale?

Merkel cell carcinoma (MCC) is a rare, highly aggressive, neuroendocrine cutaneous tumor. The incidence of MCC is growing worldwide, and the disease-related mortality is about three-fold higher than melanoma. Since a few years ago, very little has been known about this disease, and chemotherapy has been the standard of care. Nowadays, new discoveries about the pathophysiology of this neoplasm and the introduction of immunotherapy allowed to completely rewrite the history of these patients. In this review, we provide a summary of the most important changes in the management of Merkel cell carcinoma, with a focus on immunotherapy and a landscape of future treatment strategies.

Adcitmer® , a new CD56-targeting monomethyl auristatin E-conjugated antibody, is a potential therapeutic approach in Merkel cell carcinoma

BACKGROUND

Merkel cell carcinoma (MCC) is an aggressive skin cancer, whose tumour cells often express CD56. While immune checkpoint inhibitors constitute a major advance for treating patients with MCC with advanced disease, new therapeutic options are still urgently required.

OBJECTIVES

To produce and evaluate the therapeutic performance of a new antibody-drug conjugate (Adcitmer^® ) targeting CD56 in preclinical models of MCC.

METHODS

CD56 expression was evaluated in a MCC cohort (immunohistochemistry on a tissue microarray of 90 tumour samples) and MCC cell lines. Interaction of an unconjugated CD56-targeting antibody with CD56⁺ MCC cell lines was investigated by immunohistochemistry and imaging flow cytometry. Adcitmer^® product was generated by the bioconjugation of CD56-targeting antibody to a cytotoxic drug (monomethyl auristatin E) using the McSAF Inside^® bioconjugation process. The chemical properties and homogeneity of Adcitmer^® were characterized by hydrophobic interaction chromatography. Adcitmer^® cytotoxicity was evaluated in vitro and in an MCC xenograft mice model.

RESULTS

Similar to previous reports, CD56 was expressed by 66% of MCC tumours in our cohort, confirming its relevance as a therapeutic target. Specific binding and internalization of the unconjugated CD56-targeting antibody was validated in MCC cell lines. The high homogeneity of the newly generated Adcitmer^® was confirmed by hydrophobic interaction chromatography. The CD56-mediated cytotoxicity of Adcitmer^® was demonstrated in vitro in MCC cell lines. Moreover, Adcitmer^® significantly reduced tumour growth in a MCC mouse model.

CONCLUSIONS

Our study suggests that Adcitmer^® should be further assessed as a therapeutic option in patients with MCC, as an alternative therapy or combined with immune checkpoint inhibitors.

Characterizing DNA methylation signatures and their potential functional roles in Merkel cell carcinoma

BACKGROUND

Merkel cell carcinoma (MCC) is a rare but aggressive skin cancer with limited treatment possibilities. Merkel cell tumors display with neuroendocrine features and Merkel cell polyomavirus (MCPyV) infection in the majority (80%) of patients. Although loss of histone H3 lysine 27 trimethylation (H3K27me3) has been shown during MCC tumorigenesis, epigenetic dysregulation has largely been overlooked.

METHODS

We conducted global DNA methylation profiling of clinically annotated MCC primary tumors, metastatic skin tumors, metastatic lymph node tumors, paired normal tissues, and two human MCC cell lines using the Illumina Infinium EPIC DNA methylation BeadArray platform.

RESULTS

Significant differential DNA methylation patterns across the genome are revealed between the four tissue types, as well as based on MCPyV status. Furthermore, 964 genes directly regulated by promoter or gene body DNA methylation were identified with high enrichment in neuro-related pathways. Finally, our findings suggest that loss of H3K27me3 occupancy in MCC is attributed to KDM6B and EZHIP overexpression as a consequence of promoter DNA hypomethylation.

CONCLUSIONS

We have demonstrated specific DNA methylation patterns for primary MCC tumors, metastatic MCCs, and adjacent-normal tissues. We have also identified DNA methylation markers that not only show potential diagnostic or prognostic utility in MCC management, but also correlate with MCC tumorigenesis, MCPyV expression, neuroendocrine features, and H3K27me3 status. The identification of DNA methylation alterations in MCC supports the need for further studies to understand the clinical implications of epigenetic dysregulation and potential therapeutic targets in MCC.

Clinicopathologic features of cutaneous metastases from internal malignancies

Background

Cutaneous metastasis (CM) is the spread of cancer cells from a primary site to the skin and is rarely the first sign of silent cancer. We investigated the clinicopathological characteristics of CM from internal malignancies in Korean patients treated at our institution over 20 years.

Methods

The clinicopathological findings of 112 patients (62 females, 50 males) with CM diagnosed at Yeungnam University Hospital between 2000 and 2020 were retrospectively reviewed.

Results

Mean patient age was 58.6 years (range, 26 to 87 years), and the most common primary cancer site was breast (74.2%) in women and lung (36.0%) in men. Ninety-six patients (85.7%) presented with CM after primary tumor diagnosis. CM from the lung or biliary tract usually occurred within 2 years of primary tumor diagnosis, whereas metastases from the breast and kidney occurred several years later. The chest, abdomen, and scalp were common sites of CM. Breast cancer usually metastasized to chest skin, while gastrointestinal tract cancers commonly metastasized to the abdomen. The scalp was a common location for CM from various tumors. The most common dermatologic presentations were nodules and masses. Immunohistochemical studies helped identify underlying malignancies when primary tumors were unknown.

Conclusions

The relative frequency of CM parallels the overall incidence of primary malignant tumors, and CMs usually occur at anatomic sites close to the primary tumor. CM can be diagnosed based on clinical, radiological, and histological features; however, immunohistochemical study is required in some cases.

Morphologic Diversity of Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare and highly aggressive neuroendocrine carcinoma of unknown origin. We performed a retrospective histologic review of primary cutaneous MCCs diagnosed from 1997 to 2018 in several clinical institutions and literature review to determine the frequency of various unusual morphologic appearances of MCC. Of the 136 primary MCCs identified, intraepidermal carcinoma or epidermotropism was noted in 11/136 (8%) cases. An association with pilar cyst in 1/136 (0.7%) case, with actinic keratosis in 2/136 (1.5%) cases, with either invasive or in situ squamous cell carcinoma (SCC) in 14/136 (10%) cases, with poroma in 1/136 (0.7%), and with basal cell carcinoma in 1/136 (0.7%) case was noted. Trabecular pattern and rosettes were noted in 7/136 (5%) and 3/136 (2%) cases, respectively. There was one case of metastatic MCC in a lymph node with chronic lymphocytic leukemia and one rare case of metastatic MCC and SCC in a lymph node. Although uncommon, differentiation toward other cell lineage can be observed in both primary and metastatic MCCs. The tumor can assume a variety of histologic appearances including association with SCC, basal cell carcinoma, melanocytic neoplasm, and follicular cyst; as well as exhibit glandular, sarcomatous, and mesenchymal differentiation. This diversity of morphologic appearance of MCC reflects the complexity of its underlying pathogenesis.

High-grade Neuroendocrine Carcinomas of the Vulva: A Clinicopathologic Study of 16 Cases

Vulvar high-grade neuroendocrine carcinomas (HGNECs) are rare and primarily thought to represent Merkel cell carcinoma (MCC). We present the clinicopathologic features of 16 such cases, the largest series to date. Patients were most often White, postmenopausal, and symptomatic from a palpable vulvar mass/nodule. Tumors ranged from 0.7 to 6 cm and most commonly involved the labium majus. Majority of the cases were pure HGNECs (15/16) with small cell (SC) morphology (14/16); 2 were large cell neuroendocrine carcinomas, of which 1 was combined with moderately differentiated adenocarcinoma. All tumors expressed synaptophysin. Of the 14 HGNECs with SC morphology, 6 were CK20-positive MCCs with characteristic CAM5.2 and neurofilament (NF) expression. Five of these MCCs were positive for Merkel cell polyoma virus large T-antigen (MCPyVLTAg). In contrast, 6 HGNECs with SC morphology were negative for CK20, NF, and MCPyVLTAg and classified as SCNECs. High-risk human papilloma virus was positive in all SCNECs and negative in all MCCs. One case of HGNEC with SC morphology could not be entirely characterized due to lack of tissue for ancillary testing. Five of 12 (42%) cases had a discrepant diagnosis initially rendered. Most patients (10/15) presented with International Federation of Gynecology and Obstetrics stage III or IV disease. Usual sites of metastasis included inguinal lymph node, liver, bone, and lung. Twelve patients underwent surgery with adjuvant chemotherapy and/or radiation therapy, 1 received adjuvant immunotherapy, and 1 patient received neoadjuvant chemotherapy followed by surgery and adjuvant radiation therapy. Median overall survival was 24 months (range: 7 to 103 mo), and overall 5-year survival was 12% (95% confidence interval: 1% to 39%). In summary, vulvar HGNECs are rare, aggressive neoplasms that can be further subclassified into MCC, SCNEC, and large cell neuroendocrine carcinoma. CK20, CAM5.2, NF, TTF-1, MCPyVLTAg, and high-risk human papilloma virus facilitate the distinction of MCC from SCNEC. Proper identification of vulvar HGNECs is critical for patient management.

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

Importance

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

Objectives

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

Design, Setting, and Participants

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

Exposures

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

Main Outcomes and Measures

Incidence rates of Merkel cell carcinoma.

Results

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

Conclusions and Relevance

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

Merkel cell carcinoma

Merkel cell carcinoma (MCC) of the skin is a rare, aggressive form of skin cancer that metastasizes to other parts of the body. This cutaneous neuroendocrine tumour mainly affects older people, with most cases generally occurring over the age of 50 years. Merkel cell polyomavirus has been shown to induce gene mutations resulting in this skin cancer, with immunosuppression and ultraviolet radiation being other key risk factors in its pathogenesis. MCC is clinically seen as a rapidly enlarging, isolated, irregular erythematous nodule typically found on sun-exposed sites. Diagnosis is through clinical examination followed by tissue biopsy, which demonstrates characteristic histopathological neuroendocrine features. Immunohistochemistry plays a crucial role in diagnosis with the characteristic perinuclear staining with cytokeratin-20 helping to differentiate it from other morphologically similar tumours. Sentinel lymph node biopsy and imaging is essential for staging and determining prognosis. Surgical excision is the mainstay of treatment for localized disease although adjuvant radiotherapy is often required. Metastatic disease involves a very poor prognosis, and immune checkpoint inhibitors have recently shown promise in the treatment of metastatic disease. Avelumab, a monoclonal antibody that binds to the programmed death-1 receptor, has been approved by the National Institute for Health and Care Excellence and shown encouraging survival outcomes. It provides an option for treating metastatic carcinoma in adults after they have failed ≥ 1 line of chemotherapy for metastatic disease.

Merkel cell carcinoma of the eyelid and periocular region: A review

Merkel cell carcinoma (MCC) is a rare primary cutaneous neuroendocrine carcinoma with a high mortality rate. It typically affects elderly Caucasians, with a slight predilection for males. It is associated with chronic sun exposure and/or immunosuppression. Almost half of all cases occur on the head or neck and an estimated 2.5%–10% arise on the eyelids or periocular skin. It ranks as the 5^th most common malignant tumor at these sites, preceded in frequency by basal cell, squamous cell and sebaceous carcinoma, as well as melanoma. Its clinical presentation as a violaceous nodule/plaque lacks specificity, and it can be mistaken for cysts, chalazia or basal cell carcinomas. Sub-specialized histopathological and immunohistochemical evaluations are required for diagnosis. Clinical staging defines the extent of disease and governs management. This includes surgery and adjuvant radiotherapy for localized tumors and of late, immunotherapy for metastatic disease. Significant advances in our understanding of the dual etiopathogenesis (Merkel cell polyomavirus- and Ultraviolet radiation-induced) and the biology of the neoplasm have been achieved in recent years. Issuing from the tumor's known susceptibility to host immunity, a recent therapeutic breakthrough has occurred whereby immune checkpoint inhibition has been shown to mitigate advanced disease. These factors and the increased global incidence of the tumor have brought it to the forefront of medical attention. This review provides a clinically relevant update on MCC, with special reference to cases arising on the eyelid/periocular region.

Merkel cell carcinoma: A review

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