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

Updates on the diagnosis, current and future therapeutic options in Merkel-cell carcinoma

Merkel-cell carcinoma (MCC) is a rare and extremely aggressive nonmelanocytic cutaneous neuroendocrine carcinoma. Historically, it has been associated with limited therapy options and poor prognosis. While its incidence has been rising over the last two decades, recent discoveries and a better understanding of its pathogenesis, viral association and immunologic features have allowed for the emergence of new therapies. Surgical excision with or without radiotherapy remains the first-line therapy for primary lesions without evidence of metastatic disease. The majority of MCC cases are regrettably diagnosed at advanced stages and oftentimes require systemic therapy. There have been several significant advances in the treatment of MCC in the last decade. Among these have been the development of immune checkpoint inhibitors targeting the programmed death protein-1 (PD-1)/programmed death ligand-1 (PDL-1). Despite recent success of immunotherapy, nearly 50% of patients diagnosed with MCC still succumb to the disease. Fortunately, there has been a number of new targeted therapies that hold great promise. Among them are phosphatidylinositide-3kinase (Pl3K) inhibitors, adoptive T-cell immunotherapy, activated NK-92 cells infusions and therapeutic vaccines. Additional emerging therapeutic targets include cellular ubiquitin-specific processing protease 7 (Usp7) that restricts viral replication and IFN genes (STING), activation of which promotes an antitumor inflammatory response.

Merkel Cell Polyomavirus and Human Merkel Cell Carcinoma

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

DETECTing Merkel Cell Polyomavirus in Merkel Tumors

Merkel cell carcinoma (MCC) is a rare, aggressive skin cancer caused either by Merkel cell polyomavirus (MCV) T antigen expression, post-integration (~80% cases), or by UV-mediated DNA damage. Interestingly, overall survival of MCV-positive Merkel cell carcinoma patients is better, making this differential information of significant diagnostic and prognostic value. Also, MCV provides a direct target for therapy in MCC patients. Currently, the methods used for diagnosis of MCV in tumors are often discordant and unreliable. Here we used a guided molecular scissors based-DNA Endonuclease Targeted CRISPR Trans Reporter (DETECTR) technique to develop an in vitro molecular diagnostic tool for MCV-positive MCC. DETECTR couples recombinase polymerase based amplification of target MCV DNA with Cas12a mediated detection. CRISPR diagnostics couple specific detection followed by cutting of the pathogenic DNA by the Cas enzyme-gRNA complex, with non-specific cutting of ssDNA that provides a measurable visual cue. To detect MCV DNA in MCC, we designed Cas12a gRNAs targeting the MCV DNA and tested their targeting efficiency, and sensitivity using a fluorophore quencher labeled reporter assay. We show that MCV DETECTR system can detect MCV integrated in Merkel tumor rapidly, specifically and with femto-molar sensitivity. Our study is a preliminary, proof-of-principle analysis showing the use of CRISPR for MCV diagnosis. Further validation in human tumor samples is needed for its clinical use in the near future. This new system is promising and we hope it can be coupled with immunohistochemical studies to diagnose the viral status of MCC in clinics soon.

Favorable Response After Only One Cycle of Peptide Receptor Radionuclide Therapy With 177Lu-DOTATATE in a Patient With Metastatic Merkel Cell Carcinoma

A 77-year-old man with a history of metastatic Merkel cell carcinoma and debilitating painful cutaneous lesions was referred to our nuclear medicine department for peptide receptor radionuclide therapy with Lu-DOTATATE as ultimate therapeutic option. Post-treatment whole body scan showed multiple zones of Lu-DOTATATE uptake in the metastatic regions, which revealed significant improvement within the next 10 days of therapy. Peptide receptor radionuclide therapy in metastatic Merkel cell carcinoma is an effective therapeutic option that should be considered in earlier stages of the disease.

Cancer-testis antigens as biomarkers for Merkel cell carcinoma: Pitfalls and opportunities

BACKGROUND

The prognosis and treatment options for metastatic Merkel cell carcinoma (MCC) are poor. The immune-privileged status of cancer-testis (CT) antigens imparts tumor specificity, making them ideal candidates for targeted immunotherapy. We investigate the usefulness of the CT antigens SPA17 (sperm protein-17 [SP-17]), IGF2BP3 (insulin-like growth factor-II mRNA-binding protein 3 [IMP-3]), and transmembrane protein with epidermal growth factor (EGF)-like and two follistatin-like domains 1 (TMEFF1) as potential MCC biomarkers and evaluate their possible utility in immunotherapy and molecularly targeted image-guided treatment.

METHODS

The CT antigens SP-17, IMP-3, and TMEFF1 were selected using transcriptome profiling to identify CT antigens expressed in MCC tumors. Antibodies directed against these CT antigens were stained. Twelve normal skin tissue samples were used as a control. The average percentage of positive cells in each tumor was computed.

RESULTS

Twelve of 14 (86%) MCC cases showed crisp nuclear staining for SP-17, with 2.06% of cells staining positive. IMP-3 showed crisp, perinuclear staining in all 14 MCC cases, with 52.93% MCC cells staining positive. TMEFF1 showed perinuclear staining in all 14 MCC cases, with 96.51% of tumor cells staining positive.

CONCLUSIONS

CT antigens were found to be expressed in both MCC and some control tissues. SP-17 was the most specific yet the least sensitive. IMP-3 and TMEFF1 were both sensitive but not specific. CT antigens may represent valuable treatment targets in MCC.

Unusual Neuroendocrine Differentiation in a Small Round Cell Angiosarcoma: A Potential Histologic Mimicker of Superficial Ewing Sarcoma

Neuroendocrine differentiation or aberrant expression of neuroendocrine markers is very uncommon in angiosarcomas (AS) and creates a challenging differential diagnosis with other superficial or soft tissue tumors. Herein, we report a new case of superficial AS presenting as a tumor lesion on the little finger of the right hand of a 52-year-old man. The tumor displayed CD56, chromogranin-A, and synaptophysin immunoreactivity. Tumor cells were positive for vascular markers (CD31, FLI1, ERG, D2-40, VE-cadherin, VEGR1,2, and 3), CD99, and EMA, but were negative for S100, CK (AE1/AE3), CK20, polyomavirus, and myogenic (desmin and myogenin) and melanocyte markers (melan-A and HMB45). Ki67 immunostains indicated high proliferative activity (>50%). The whole-body computed tomography did not reveal distant disease. The initial assessment considered several tumor subtypes as possible histological diagnoses, including Ewing sarcoma, Ewing-like sarcoma, Merkel cell carcinoma, and undifferentiated "small round cell sarcoma". Fluorescence in situ hybridization analysis was negative for EWSR1 translocation and molecular analysis failed to detect any EWSR1, CIC, SYT or BCOR rearrangement. As a follow-up investigation, we tested 17 cutaneous/superficial AS for neuroendocrine markers; however, only one of these showed focal CD56 and synaptophysin expression. In conclusion, the present findings indicate that neuroendocrine differentiation is a very infrequent feature in AS. We report an AS of the finger with an uncommon histological appearance and immunohistochemical profile: predominant round cell tumor proliferation and neuroendocrine differentiation. Pathologists should be aware of these potential histological and immunohistochemical pitfalls in AS.

A rare case of Merkel cell carcinoma presenting as a giant intra-thoracic mass: A case report and review of the literature

RATIONALE

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine-derived cutaneous cancer. Ectopic or single metastatic MCC located in thorax is extremely rare; meanwhile, its definite management has not been elucidated yet.

PATIENT CONCERNS

A 64-year-old female patient with a giant mass located in her left thorax was presented for stuffy pain of left chest for 6 months and fever for half a month. She underwent radical resection of vulvar MCC 10 years ago.

DIAGNOSES

Computed tomography (CT)-guided biopsy of the intrathoracic mass revealed a diagnosis of MCC, without synchronous urogenital lesions on pelvic CT images.

INTERVENTIONS

This bulky tumor was completely resected via thoracotomy, along with the adjacent pulmonary lobe, pericardium, pleura, and diaphragm.

OUTCOMES

The patient survived without local-regional recurrence or distant metastasis during the follow-up of 1 year up to now.

LESSONS

Ectopic or single metastatic MCC should be considered in the differential diagnosis of intrathoracic tumors, especially in patients with a history of MCC. Besides, a timely surgery combined with chemotherapy is effective for this disease.

Merkel Cell Polyomavirus: A New DNA Virus Associated with Human Cancer

Merkel cell polyomavirus (MCPyV or MCV) is a novel human polyomavirus that has been discovered in Merkel cell carcinoma (MCC), a highly aggressive skin cancer. MCPyV infection is widespread in the general population. MCPyV-associated MCC is one of the most aggressive skin cancers, killing more patients than other well-known cancers such as cutaneous T-cell lymphoma and chronic myelogenous leukemia (CML). Currently, however, there is no effective drug for curing this cancer. The incidence of MCC has tripled over the past two decades. With the widespread infection of MCPyV and the increase in MCC diagnoses, it is critical to better understand the biology of MCPyV and its oncogenic potential. In this chapter, we summarize recent discoveries regarding MCPyV molecular virology, host cellular tropism, mechanisms of MCPyV oncoprotein-mediated oncogenesis, and current therapeutic strategies for MCPyV-associated MCC. We also present epidemiological evidence for MCPyV infection in HIV patients and links between MCPyV and non-MCC human cancers.

Merkel cell carcinoma cardiac metastasis causing cardiac tamponade

We describe an unusual presentation of Merkel cell carcinoma (MCC), a rare neuroendocrine cutaneous tumour. A 59-year-old man presented with a 2-week history of dyspnoea on a background of MCC of the left elbow that was diagnosed after an axillary lymph node metastasis had appeared. He was clinically diagnosed with cardiac tamponade and received urgent pericardiocentesis. Thoracic CT imaging revealed a large infiltrating mass within the inferior aspect of the heart, confirmed to be MCC via immunohistochemistry of the pericardial fluid. On review of prior fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) imaging, avid uptake was evident at the corresponding site of disease. This case has several important illustrative aspects, including the clinical manifestations of cardiac metastases, the challenges of MCC histopathological diagnosis and the role of imaging (in particular FDG-PET) in this aggressive disease.

Seeking Standards for the Detection of Merkel Cell Polyomavirus and its Clinical Significance

Merkel cell carcinoma is a rare skin cancer associated with Merkel cell polyomavirus in most cases. Prior studies associating Merkel cell carcinoma viral status with prognosis have inconsistent findings. Moshiri et al. used multimodal virus detection to determine that the 81% of patients with virus-positive Merkel cell carcinoma tumors had earlier stage disease and better outcomes relative to virus-negative cases.

EUS-FNA of the Merkel cell carcinoma metastasis to the pancreas: Cytomorphology and immunocytochemistry on direct cytological smears

OBJECTIVE

To report two cases of Merkel cell carcinoma (MCC) metastatic to the pancreas diagnosed with endoscopic ultrasound-guided-fine needle aspiration (EUS-FNA) and to add the case of concomitant chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL/SLL) and MCC to the literature. The aim is to alert the cytopathologists once more to the problems of differential diagnosis of pancreatic metastasis of MCC and to describe the possibilities of ancillary methods performed on direct cytological smears.

METHODS

EUS-FNA procedures were performed according to standard institution protocol, using 22-G needles with cytopathologist on-site. Based on rapid on-site evaluation (ROSE), additional passes were made for immunocytochemistry (ICC). A mini panel of antibodies was used to aid the differential diagnosis.

RESULTS

Smears revealed a dispersed pattern of small round cells with scant cytoplasm, round nuclei with inconspicuous nucleoli and occasional nuclear moulding, suspicious of small cell carcinoma. Results of ICC applied to the direct cytological smears were as follows: LCA negative, Cytokeratin (clone MNF116) positive, TTF-1 negative, CD 56 positive, NSE weakly positive, Chromogranin A weakly positive and CK20 positive, in one case in a dot-like perinuclear pattern. The diagnosis of MCC was made.

CONCLUSION

Increasing incidence of MCC warrants the inclusion of MCC in the differential diagnosis of tumours of small round blue cell morphology even in unusual sites. The cytomorphological features coupled with an ICC panel are usually enough to make a confident diagnosis of MCC. EUS-FNA is a minimally invasive technique which enables sampling adequate tissue for all the ancillary methods eventually needed to support the diagnosis.