CD8+ lymphocyte intratumoral infiltration as a stage-independent predictor of Merkel cell carcinoma survival: a population-based study

Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine skin cancer that is highly radiosensitive and immunogenic. Immunotherapy is the primary treatment of advanced disease, and immune checkpoint inhibitors show promise as neoadjuvant or adjuvant therapy in patients with high-risk resectable MCC. Emerging biomarkers of tumor burden are becoming increasingly important in identifying high-risk patients and in post-treatment surveillance. Further research is needed to determine the optimal duration of anti-PD-(L)1 treatment and second-line options for patients with MCC refractory to immunotherapy. This review covers the characteristics and management of MCC including recent innovations and areas of active investigation.

Development of a Multiplex Immunofluorescence Assay for Tumor Microenvironment Studies of Human and Murine Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine carcinoma. Checkpoint inhibitor immunotherapy plays an essential role in management of advanced MCC; however, predictors of immunotherapy response remain poorly defined. Syngeneic mouse models suitable for testing novel immunotherapy and combination therapy approaches are likely to soon become available and will require assays for evaluating the tumor microenvironment (TME). Multiplex immunofluorescence (mIF) is a powerful approach to characterize the TME for understanding immunotherapy responses and immune surveillance. In this method article, we provide detailed instructions on assay development for mIF, using as examples 2 new mIF panels for TME investigations of human and murine MCC tumors. Specifically, we demonstrate panels that allow simultaneous visualization of the Merkel cell master transcription factor SOX2 for tumor cell identification, alongside T-cell markers (CD3, CD8, and FOXP3), macrophage markers (F4/80 for mouse and CD163 for human tumors), together with the checkpoint marker PD-L1 for human tumors, and the myeloid-derived suppressor cell marker Arg1 for mouse tumors. We provide detailed protocols for investigators to incorporate these mIF panels into their investigations of human and murine MCC. We also provide fundamental guidance for mIF assay development that will be broadly useful for investigators who consider modifying the panels presented in this study or developing their own mIF panels.

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.

Merkel Cell Carcinoma: Integrating Epidemiology, Immunology, and Therapeutic Updates

Merkel cell carcinoma (MCC) is a rare skin cancer characterized by neuroendocrine differentiation. Its carcinogenesis is based either on the integration of the Merkel cell polyomavirus or on ultraviolet (UV) mutagenesis, both of which lead to high immunogenicity either through the expression of viral proteins or neoantigens. Despite this immunogenicity resulting from viral or UV-associated carcinogenesis, it exhibits highly aggressive behavior. However, owing to the rarity of MCC and the lack of epidemiologic registries with detailed clinical data, there is some uncertainty regarding the spontaneous course of the disease. Historically, advanced MCC patients were treated with conventional cytotoxic chemotherapy yielding a median response duration of only 3 months. Starting in 2017, four programmed cell death protein 1 (PD-1)/programmed cell death-ligand 1 (PD-L1) immune checkpoint inhibitors-avelumab, pembrolizumab, nivolumab (utilized in both neoadjuvant and adjuvant settings), and retifanlimab-have demonstrated efficacy in treating patients with disseminated MCC on the basis of prospective clinical trials. However, generating clinical evidence for rare cancers, such as MCC, is challenging owing to difficulties in conducting large-scale trials, resulting in small sample sizes and therefore lacking statistical power. Thus, to comprehensively understand the available clinical evidence on various immunotherapy approaches for MCC, we also delve into the epidemiology and immune biology of this cancer. Nevertheless, while randomized studies directly comparing immune checkpoint inhibitors and chemotherapy in MCC are lacking, immunotherapy shows response rates comparable to those previously reported with chemotherapy but with more enduring responses. Notably, adjuvant nivolumab has proven superiority to the standard-of-care therapy (observation) in the adjuvant setting.

Characterization of Immunosuppressive Myeloid Cells in Merkel Cell Carcinoma: Correlation with Resistance to PD-1 Pathway Blockade

PURPOSE

Merkel cell carcinoma (MCC) is a highly immunogenic skin cancer. Although essentially all MCCs are antigenic through viral antigens or high tumor mutation burden, MCC has a response rate of only approximately 50% to PD-(L)1 blockade suggesting barriers to T-cell responses. Prior studies of MCC immunobiology have focused on CD8 T-cell infiltration and their exhaustion status, while the role of innate immunity, particularly myeloid cells, in MCC remains underexplored.

EXPERIMENTAL DESIGN

We utilized single-cell transcriptomics from 9 patients with MCC and multiplex IHC staining of 54 patients' preimmunotherapy tumors, to identify myeloid cells and evaluate association with immunotherapy response.

RESULTS

Single-cell transcriptomics identified tumor-associated macrophages (TAM) as the dominant myeloid component within MCC tumors. These TAMs express an immunosuppressive gene signature characteristic of monocytic myeloid-derived suppressor cells and importantly express several targetable immune checkpoint molecules, including PD-L1 and LILRB receptors, that are not present on tumor cells. Analysis of 54 preimmunotherapy tumor samples showed that a subset of TAMs (CD163+, CD14+, S100A8+) selectively infiltrated tumors that had significant CD8 T cells. Indeed, higher TAM prevalence was associated with resistance to PD-1 blockade. While spatial interactions between TAMs and CD8 T cells were not associated with response, myeloid transcriptomic data showed evidence for cytokine signaling and expression of LILRB receptors, suggesting potential immunosuppressive mechanisms.

CONCLUSIONS

This study further characterizes TAMs in MCC tumors and provides insights into their possible immunosuppressive mechanism. TAMs may reduce the likelihood of treatment response in MCC by counteracting the benefit of CD8 T-cell infiltration. See related commentary by Silk and Davar, p. 1076.

Merkel cell polyomavirus-specific and CD39+CLA+ CD8 T cells as blood-based predictive biomarkers for PD-1 blockade in Merkel cell carcinoma

Merkel cell carcinoma is a skin cancer often driven by Merkel cell polyomavirus (MCPyV) with high rates of response to anti-PD-1 therapy despite low mutational burden. MCPyV-specific CD8 T cells are implicated in anti-PD-1-associated immune responses and provide a means to directly study tumor-specific T cell responses to treatment. Using mass cytometry and combinatorial tetramer staining, we find that baseline frequencies of blood MCPyV-specific cells correlated with response and survival. Frequencies of these cells decrease markedly during response to therapy. Phenotypes of MCPyV-specific CD8 T cells have distinct expression patterns of CD39, cutaneous lymphocyte-associated antigen (CLA), and CD103. Correspondingly, overall bulk CD39+CLA+ CD8 T cell frequencies in blood correlate with MCPyV-specific cell frequencies and similarly predicted favorable clinical outcomes. Conversely, frequencies of CD39+CD103+ CD8 T cells are associated with tumor burden and worse outcomes. These cell subsets can be useful as biomarkers and to isolate blood-derived tumor-specific T cells.

T antigen-specific CD8+ T cells associate with PD-1 blockade response in virus-positive Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a highly immunogenic skin cancer primarily induced by Merkel cell polyomavirus, which is driven by the expression of the oncogenic T antigens (T-Ags). Blockade of the programmed cell death protein-1 (PD-1) pathway has shown remarkable response rates, but evidence for therapy-associated T-Ag-specific immune response and therapeutic strategies for the nonresponding fraction are both limited. We tracked T-Ag-reactive CD8+ T cells in peripheral blood of 26 MCC patients under anti-PD1 therapy, using DNA-barcoded pMHC multimers, displaying all peptides from the predicted HLA ligandome of the oncoproteins, covering 33 class I haplotypes. We observed a broad T cell recognition of T-Ags, including identification of 20 T-Ag-derived epitopes we believe to be novel. Broadening of the T-Ag recognition profile and increased T cell frequencies during therapy were strongly associated with clinical response and prolonged progression-free survival. T-Ag-specific T cells could be further boosted and expanded directly from peripheral blood using artificial antigen-presenting scaffolds, even in patients with no detectable T-Ag-specific T cells. These T cells provided strong tumor-rejection capacity while retaining a favorable phenotype for adoptive cell transfer. These findings demonstrate that T-Ag-specific T cells are associated with the clinical outcome to PD-1 blockade and that Ag-presenting scaffolds can be used to boost such responses.

Review of Merkel cell carcinoma with solitary pancreatic metastases mimicking primary neuroendocrine tumor of the pancreas

OBJECTIVE/BACKGROUND

Merkel cell carcinoma (MCC) but metastases to the pancreas are very rare. There are only a few cases of isolated metastases of MCC to the pancreas. Because of this rarity, it can be wrongly diagnosed as a neuroendocrine tumor of the pancreas(pNET), especially the poorly differentiated neuroendocrine carcinoma (PNEC) subtype, in which the treatment is vastly different than that of MCC with isolated metastases of the pancreas.

METHODS

An electronic search of the PubMed and google scholar databases was performed to obtain the literature on MCC with pancreatic metastases, using the following search terms: Merkel cell carcinoma, pancreas, and metastases. Results are limited to the following available article types: case reports and case series. We identified 45 cases of MCC with pancreatic metastases from the PubMed and Google Scholar database search and examined their potential relevance. Only 22 cases with isolated pancreatic metastases were taken for review including one case that we encountered.

RESULTS

The results from our review of cases of isolated pancreatic metastases of MCC were compared to the characteristics of the poorly differentiated pancreatic neuroendocrine tumor (PNEC). We found the following: (a) MCC with isolated pancreatic metastases occurred at an older age than PNEC and with male gender predominance (b) Most of the metastases occurred within 2 years of initial diagnosis of MCC (c) Resection of pancreatic mass was the first line treatment in case of resectable PNECs whereas resection of metastases was infrequently performed in MCC with pancreatic metastases.

Clinical significance of the expression of FOXP3 and TIGIT in Merkel cell carcinoma

The pathogenesis of 80% of Merkel cell carcinoma (MCC) cases is associated with Merkel cell polyomavirus (MCPyV). Forkhead helix transcription factor P3 (FOXP3) and the T cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibition motif domains (TIGIT)-CD155 pathway, which are targets for immunotherapy, were assessed as prognostic factors of MCC. We analyzed mRNA expression data of 111 patients with MCC and performed immunohistochemical analysis to detect the expression of programmed death ligand 1 (PD-L1), CD8, FOXP3, TIGIT, and CD155 in 65 cases of MCC. In CD8 and FOXP3 immunostaining, the number of expressing-infiltrating cells was determined by dividing the region into tumor center and invasive front areas. FOXP3 expression was evaluated separately in cells with high and low intensities. Aberrant TIGIT expression and weak CD155 staining were observed in MCC cells. CD8- and FOXP3-positive cell infiltrations were higher in the invasive front than in the tumor center. Multivariate Cox hazard analysis revealed that high infiltration of cells with low-intensity FOXP3 expression in the invasive front is a favorable prognostic factor (p = 0.025). Thus, targeting TIGIT-CD155 signaling and FOXP3 as well as PD-L1 may be a therapeutic strategy for MCC.

Current and preclinical treatment options for Merkel cell carcinoma

INTRODUCTION

Merkel cell carcinoma (MCC) is a rare, highly aggressive form of skin cancer with neuroendocrine features. The origin of this cancer is still unclear, but research in the last 15 years has demonstrated that MCC arises via two distinct etiologic pathways, i.e. virus and UV-induced. Considering the high mortality rate and the limited therapeutic options available, this review aims to highlight the significance of MCC research and the need for advancement in MCC treatment.

AREAS COVERED

With the advent of the immune checkpoint inhibitor therapies, we now have treatment options providing a survival benefit for patients with advanced MCC. However, the issue of primary and acquired resistance to these therapies remains a significant concern. Therefore, ongoing efforts seeking additional therapeutic targets and approaches for MCC therapy are a necessity. Through a comprehensive literature search, we provide an overview on recent preclinical and clinical studies with respect to MCC therapy.

EXPERT OPINION

Currently, the only evidence-based therapy for MCC is immune checkpoint blockade with anti-PD-1/PD-L1 for advanced patients. Neoadjuvant, adjuvant and combined immune checkpoint blockade are promising treatment options.

Merkel Cell Carcinoma-Update on Diagnosis, Management and Future Perspectives

MCC is a rare but highly aggressive skin cancer. The identification of the driving role of Merkel cell polyomavirus (MCPyV) and ultraviolet-induced DNA damage in the oncogenesis of MCC allowed a better understanding of its biological behavior. The presence of MCPyV-specific T cells and lymphocytes exhibiting an 'exhausted' phenotype in the tumor microenvironment along with the high prevalence of immunosuppression among affected patients are strong indicators of the immunogenic properties of MCC. The use of immunotherapy has revolutionized the management of patients with advanced MCC with anti-PD-1/PD L1 blockade, providing objective responses in as much as 50-70% of cases when used in first-line treatment. However, acquired resistance or contraindication to immune checkpoint inhibitors can be an issue for a non-negligible number of patients and novel therapeutic strategies are warranted. This review will focus on current management guidelines for MCC and future therapeutic perspectives for advanced disease with an emphasis on molecular pathways, targeted therapies, and immune-based strategies. These new therapies alone or in combination with anti-PD-1/PD-L1 inhibitors could enhance immune responses against tumor cells and overcome acquired resistance to immunotherapy.

T-Cell Mediated Immunity in Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare and frequently lethal skin cancer with neuroendocrine characteristics. MCC can originate from either the presence of MCC polyomavirus (MCPyV) DNA or chronic ultraviolet (UV) exposure that can cause DNA mutations. MCC is predominant in sun-exposed regions of the body and can metastasize to regional lymph nodes, liver, lungs, bone, and brain. Older, light-skinned individuals with a history of significant sun exposure are at the highest risk. Previous studies have shown that tumors containing a high number of tumor-infiltrating T-cells have favorable survival, even in the absence of MCPyV DNA, suggesting that MCPyV infection enhances T-cell infiltration. However, other factors may also play a role in the host antitumor response. Herein, we review the impact of tumor infiltrating lymphocytes (TILs), mainly the CD4⁺, CD8⁺, and regulatory T-cell (Tregs) responses on the course of MCC, including their role in initiating MCPyV-specific immune responses. Furthermore, potential research avenues related to T-cell biology in MCC, as well as relevant immunotherapies are discussed.

Identifying Candidates for Immunotherapy among Patients with Non-Melanoma Skin Cancer: A Review of the Potential Predictors of Response

BACKGROUND

Non-melanoma skin cancer (NMSC) stands as an umbrella term for common cutaneous malignancies, including basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC), together with rarer cutaneous cancers, such as Merkel cell carcinoma (MCC) and other forms of adnexal cancers. The majority of NMSCs can be successfully treated with surgery or radiotherapy, but advanced and metastatic stages may require systemic approaches such as immunotherapy with immune checkpoint inhibitors (ICIs).

SUMMARY

Since immunotherapy is not effective in all patients and can potentially lead to severe adverse effects, an important clinical question is how to properly identify those who could be suitable candidates for this therapeutic choice. In this paper, we review the potential features and biomarkers used to predict the outcome of ICIs therapy for NMSCs. Moreover, we analyze the role of immunotherapy in special populations, such as the elderly, immunocompromised patients, organ transplant recipients, and subjects suffering from autoimmune conditions.

KEY MESSAGES

Many clinical, serum, histopathological, and genetic features have been investigated as potential predictors of response in NMSCs treated with ICIs. Although this field of research is very promising, definitive, cost-effective, and reproducible biomarkers are still lacking and further efforts are needed to validate the suggested predictors in larger cohorts.

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.

Clinical-Pathological Evaluation and Prognostic Analysis of 228 Merkel Cell Carcinomas Focusing on Tumor-Infiltrating Lymphocytes, MCPYV Infection and ALK Expression

Merkel cell carcinoma is a rare and aggressive primary neuroendocrine carcinoma of the skin, whose pathogenesis can be traced back to UV radiation damage or Merkel cell polyomavirus (MCPyV) infection. Despite some improvements on the characterization of the disease partly due to its increased incidence, crucial pathogenetic and prognostic factors still need to be refined. A consecutive series of 228 MCC from three hospitals in Turin was collected with the aim of both analyzing the apparent increase in MCC incidence in our area and investigating the distribution and prognostic role of clinical-pathological parameters, with a focus on MCPyV status, ALK tumor expression and tumor infiltrating lymphocytes (TILs). Review of morphology and conventional immunohistochemical staining was possible in 191 cases. In 50 cases, the expression of the novel neuroendocrine marker INSM1 was additionally assessed. Fourteen cases of MCC of unknown primary skin lesion were identified and separately analyzed. While confirming an exponential trend in MCC incidence in the last decades and providing a description of histological and cytological features of a large series of MCC, the present study concludes that 1) INSM1 is a highly sensitive marker in both skin and lymph node primary MCC; 2) positive MCPyV status, brisk TILs and lower tumor size and thickness are independent positive prognostic parameters, and the combination of the former two may provide a novel tool for prognostic stratification; 3) ALK is expressed 87% of MCC and associated with positive viral status, and could represent a prognostic biomarker, if validated in larger series.

A web-based predictive model for overall survival of patients with cutaneous Merkel cell carcinoma: A population-based study

BACKGROUND

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine carcinoma with a high mortality rate, so it is necessary to create models to predict overall survival of MCC. We developed an easy-to-use web-based calculator to predict the OS of MCC patients based on the nomogram.

METHODS

MCC patients between 2004 and 2015 were collected from the Surveillance, Epidemiology, and End Results (SEER) database and randomly assigned to training and validation cohorts. Patients between 2016-2017 serve as the external validation cohort. Relevant risk factors were identified by univariate and multivariate COX hazards regression methods and combined to produce nomograms. The concordance index (C-index), area under the receiver operating characteristic (AUC) curve, and calibration plots have demonstrated the predictive power of the nomograms. Decision curve analysis (DCA) was used to measure nomograms in clinical practice. Patients were divided into three groups according to the scores of the nomogram.

RESULTS

A total of 3480 patients were randomly assigned to the training group and validation group in this study. Meaningful prognostic factors were applied to the establishment of nomograms. The C-index for OS was 0.725 (95% CI: 0.706-0.741) in the training cohort and 0.710 (95% CI: 0.683-0.737) in the validation cohort. In the external validation cohort, C-index was 0.763 (95% CI: 0.734-0.792). The C-index of training cohort, validation cohort and external validation cohort for CSS were 0.743 (95% CI:0.725-0.761), 0.739(95%CI:0.712-0.766) and 0.774 (95%CI:0.735-0.813), respectively. The AUC and calibration plots of 1-, 3-, and 5-year OS rates showed that the nomogram had good predictive power. DCA demonstrated that the nomogram constructed in this study could provide a clinical net benefit. Our calculator demonstrated excellent predictive capabilities for better risk grouping of MCC patients.

CONCLUSION

We created novel nomograms of prognostic factors for MCC, which more accurately and comprehensively predicted 1-, 3-, and 5-year OS/CSS in MCC patients. We established a calculator which can easily and quickly calculate the risk grouping of MCC patients by inputting clinically relevant characteristics. This can help clinicians identify high-risk patients as early as possible, carry out personalized treatment, follow-up, and monitoring, and improve the survival rate of MCC patients.

Merkel Cell Carcinoma: An updated review of pathogenesis, diagnosis, and treatment options

Merkel cell carcinoma is a rare neuroendocrine carcinoma that typically appears in sun-exposed areas of the elderly. It has a poor prognosis and with its incidence projected to increase, it is vital for dermatologists to remain up to date with recent updates in this malignancy's pathogenesis and treatment. In the past few decades Merkel cell carcinoma's pathogenesis, more specifically its relation to the Merkel cell polyomavirus, has sparked further interest in the study of this carcinoma. Most cases are attributed to malignant transformation secondary to the Merkel cell polyomavirus, with a minority derived from DNA damage resulting from ultraviolet radiation. Investigators have also determined that there are immunologic influences in the development and prognosis of Merkel cell carcinoma, as individuals with HIV, solid organ transplants, and lymphoproliferative malignancies are at a greater risk of developing this carcinoma. Also, this immunologic link carries treatment value, as immunologic therapies are currently being investigated. This article provides a comprehensive review of the epidemiology and pathogenesis of Merkel cell carcinoma as well as the current treatments available and clinical trials underway. We also touch upon the updated National Comprehensive Cancer Network Clinical Practice Guidelines in Oncology in respect to its diagnosis and recommended treatment modalities.

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.

Merkel Cell Carcinoma of the Head and Neck: Epidemiology, Pathogenesis, Current State of Treatment and Future Directions

Merkel cell carcinoma (MCC) is a rare, cutaneous neuroendocrine malignancy with increasing incidence. The skin of the head and neck is a common subsite for MCC with distinctions in management from other anatomic areas. Given the rapid pace of developments regarding MCC pathogenesis (Merkel cell polyoma virus (MCPyV)-positive or virus-negative, cell of origin), diagnosis, staging and treatment, and up to date recommendations are critical for optimizing outcomes. This review aims to summarize currently available literature for MCC of the head and neck. The authors reviewed current literature, including international guidelines regarding MCC pathogenesis, epidemiology, diagnosis, staging, and treatment. Subsequently recommendations were derived including the importance of baseline imaging, MCPyV serology testing, primary site surgery, nodal evaluation, radiotherapy, and the increasing role of immune modulating agents in MCC. MCPyV serology testing is increasingly important with potential distinctions in treatment response and surveillance between virus-positive and virus-negative MCC. Surgical management continues to balance optimizing local control with minimal morbidity. Similarly, radiotherapy continues to have importance in the adjuvant, definitive, and palliative setting for MCC of the head and neck. Immunotherapy has changed the paradigm for advanced MCC, with increasing work focusing on optimizing outcomes for non-responders and high-risk patients, including those with immunosuppression.

Intersection of Two Checkpoints: Could Inhibiting the DNA Damage Response Checkpoint Rescue Immune Checkpoint-Refractory Cancer?

Metastatic cancers resistant to immunotherapy require novel management strategies. DNA damage response (DDR) proteins, including ATR (ataxia telangiectasia and Rad3-related), ATM (ataxia telangiectasia mutated) and DNA-PK (DNA-dependent protein kinase), have been promising therapeutic targets for decades. Specific, potent DDR inhibitors (DDRi) recently entered clinical trials. Surprisingly, preclinical studies have now indicated that DDRi may stimulate anti-tumor immunity to augment immunotherapy. The mechanisms governing how DDRi could promote anti-tumor immunity are not well understood; however, early evidence suggests that they can potentiate immunogenic cell death to recruit and activate antigen-presenting cells to prime an adaptive immune response. Merkel cell carcinoma (MCC) is well suited to test these concepts. It is inherently immunogenic as ~50% of patients with advanced MCC persistently benefit from immunotherapy, making MCC one of the most responsive solid tumors. As is typical of neuroendocrine cancers, dysfunction of p53 and Rb with upregulation of Myc leads to the very rapid growth of MCC. This suggests high replication stress and susceptibility to DDRi and DNA-damaging agents. Indeed, MCC tumors are particularly radiosensitive. Given its inherent immunogenicity, cell cycle checkpoint deficiencies and sensitivity to DNA damage, MCC may be ideal for testing whether targeting the intersection of the DDR checkpoint and the immune checkpoint could help patients with immunotherapy-refractory cancers.

First-line avelumab in a cohort of 116 patients with metastatic Merkel cell carcinoma (JAVELIN Merkel 200): primary and biomarker analyses of a phase II study

BACKGROUND

Avelumab (anti-programmed death ligand 1 (PD-L1)) is approved in multiple countries for the treatment of metastatic Merkel cell carcinoma (mMCC), a rare and aggressive skin cancer. We report efficacy and safety data and exploratory biomarker analyses from a cohort of patients with mMCC treated with first-line avelumab in a phase II trial.

METHODS

Patients with treatment-naive mMCC received avelumab 10 mg/kg intravenously every 2 weeks. The primary endpoint was durable response, defined as objective response (complete or partial response; assessed by independent review) lasting ≥6 months. Additional assessments included progression-free survival (PFS), overall survival (OS), safety, and biomarker analyses.

RESULTS

In 116 patients treated with avelumab, median follow-up was 21.2 months (range: 14.9-36.6). Thirty-five patients had a response lasting ≥6 months, giving a durable response rate of 30.2% (95% CI: 22.0% to 39.4%). The objective response rate was 39.7% (95% CI: 30.7% to 49.2%). Median PFS was 4.1 months (95% CI: 1.4 to 6.1) and median OS was 20.3 months (95% CI: 12.4 to not estimable). Response rates were numerically higher in patients with PD-L1+ tumors, Merkel cell polyomavirus (MCPyV)-negative tumors, and tumors with increased intratumoral CD8+ T-cell density. Exploratory analyses did not identify a biomarker that could reliably predict a response to first-line treatment with avelumab; however, a novel gene expression signature to identify the presence of MCPyV+ tumors was derived. Treatment-related adverse events (any grade) occurred in 94 (81.0%) patients, including grade 3/4 events in 21 (18.1%) patients; no treatment-related deaths occurred.

CONCLUSION

In patients with mMCC, first-line treatment with avelumab led to responses in 40% and durable responses in 30%, and was associated with a low rate of grade 3/4 treatment-related adverse events.

The prognostic significance of PD-L1 expression on tumor and immune cells in Merkel cell carcinoma

INTRODUCTION

The aim of this study was to evaluate prognostic factors in patients with non-metastatic Merkel cell carcinoma (MCC), with a particular focus on immunological markers such as TILs subtyping (CD3, CD8, CD68, FoxP3, PD-L1 and PD-1) and MCPyV.

METHODS

Patients treated for a non-metastatic MCC with oncologic surgical resection followed or not by adjuvant radiotherapy between 01/2007 and 12/2018 were analyzed. Local and regional control (LC, RC), distant metastasis-free survival (DMFS) and overall survival (OS) were evaluated. Clinical variables analyzed included age, gender, performance status, comorbidity, tumor size, location and presentation type, extension, oncologic resection and adjuvant radiotherapy. Pathological variables analyzed included type of tumor-infiltrating lymphocytes, CD3, CD8, CD68, PD-L1 expression on immune cells and tumors cells, PD-1, FoxP3 and MCPyV, assessed with immunohistochemistry (IHC).

RESULTS

77 patients were included. After a median follow-up of 18 months (range 0.2-144), the 1-year LC, RC, DMFS and OS were 83%, 60%, 82% and 75%, respectively. In multivariate analysis, a percentage of PD-L1 expression by immune cells ≥ 1% was significantly correlated with improvement of RC (p = 0.012), DMFS (p = 0.003) and OS (p = 0.006). Adjuvant radiotherapy significantly improved DMFS (p = 0.021) and OS (0.041) rates. There was a correlation between the presence of MCPyV + and the expression of PD-L1 on IC (p = 0.05) and TC (p = 0.03).

CONCLUSION

PD-L1 expression by immune and tumor cells in non-metastatic MCC seems to significantly improve outcome in patients who did not received PD-1/PD-L1 inhibitors. Prospective studies are needed to confirm our hypothesis.

Virus-Driven Carcinogenesis

Cancer arises from the accumulation of genetic and epigenetic alterations. Even in the era of precision oncology, carcinogens contributing to neoplastic process are still an important focus of research. Comprehensive genomic analyses have revealed various combinations of base substitutions, referred to as the mutational signatures, in cancer. Each mutational signature is believed to arise from specific DNA damage and repair processes, including carcinogens. However, as a type of carcinogen, tumor viruses increase the cancer risk by alternative mechanisms, including insertional mutagenesis, viral oncogenes, and immunosuppression. In this review, we summarize virus-driven carcinogenesis to provide a framework for the control of malignant cell proliferation. We first provide a brief overview of oncogenic viruses and describe their implication in virus-related tumors. Next, we describe tumor viruses (HPV, Human papilloma virus; HBV, Hepatitis B virus; HCV, Hepatitis C virus; EBV, Epstein-Barr virus; Kaposi sarcoma herpesvirus; MCV, Merkel cell polyoma virus; HTLV-1, Human T-cell lymphotropic virus, type-1) and tumor virus-related cancers. Lastly, we introduce emerging tumor virus candidates, human cytomegalovirus (CMV), human herpesvirus-6 (HHV-6) and adeno-associated virus-2 (AAV-2). We expect this review to be a hub in a complex network of data for virus-associated carcinogenesis.

Immunotherapy and Gene Therapy for Oncoviruses Infections: A Review

Immunotherapy has been shown to be highly effective in some types of cancer caused by viruses. Gene therapy involves insertion or modification of a therapeutic gene, to correct for inappropriate gene products that cause/may cause diseases. Both these types of therapy have been used as alternative ways to avoid cancers caused by oncoviruses. In this review, we summarize recent studies on immunotherapy and gene therapy including the topics of oncolytic immunotherapy, immune checkpoint inhibitors, gene replacement, antisense oligonucleotides, RNA interference, clustered regularly interspaced short palindromic repeats Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based gene editing, transcription activator-like effector nucleases (TALENs) and custom treatment for Epstein-Barr virus, human T-lymphotropic virus 1, hepatitis B virus, human papillomavirus, hepatitis C virus, herpesvirus associated with Kaposi's sarcoma, Merkel cell polyomavirus, and cytomegalovirus.

Quality Is King: Fundamental Insights into Tumor Antigenicity from Virus-Associated Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare skin malignancy that is a paradigm cancer for solid tumor immunotherapy. MCCs associated with Merkel cell polyomavirus (virus-positive MCC [VP-MCC]) or chronic UV exposure (virus-negative MCC [VN-MCC]) are anti-PD(L)1 responsive, despite VP-MCC's low mutational burden. This suggests that antigen quality, not merely mutation quantity, dictates immunotherapy responsiveness, and cell-based therapies targeting optimal antigens may be effective. Despite VP-MCC's antigenic homogeneity, diverse T-cell infiltration patterns are observed, implying microenvironment plasticity and multifactorial contributions to immune recognition. Moreover, VP-MCC exemplifies how antitumor adaptive immunity can provide tumor burden biomarkers for early detection and disease monitoring.

γδ T Cells in Merkel Cell Carcinomas Have a Proinflammatory Profile Prognostic of Patient Survival

Merkel cell carcinomas (MCC) are immunogenic skin cancers associated with viral infection or UV mutagenesis. To study T-cell infiltrates in MCC, we analyzed 58 MCC lesions from 39 patients using multiplex-IHC/immunofluorescence (m-IHC/IF). CD4⁺ or CD8⁺ T cells comprised the majority of infiltrating T lymphocytes in most tumors. However, almost half of the tumors harbored prominent CD4/CD8 double-negative (DN) T-cell infiltrates (>20% DN T cells), and in 12% of cases, DN T cells represented the majority of T cells. Flow cytometric analysis of single-cell suspensions from fresh tumors identified DN T cells as predominantly Vδ2^- γδ T cells. In the context of γδ T-cell inflammation, these cells expressed PD-1 and LAG3, which is consistent with a suppressed or exhausted phenotype, and CD103, which indicates tissue residency. Furthermore, single-cell RNA sequencing (scRNA-seq) identified a transcriptional profile of γδ T cells suggestive of proinflammatory potential. T-cell receptor (TCR) analysis confirmed clonal expansion of Vδ1 and Vδ3 clonotypes, and functional studies using cloned γδ TCRs demonstrated restriction of these for CD1c and MR1 antigen-presenting molecules. On the basis of a 13-gene γδ T-cell signature derived from scRNA-seq analysis, gene-set enrichment on bulk RNA-seq data showed a positive correlation between enrichment scores and DN T-cell infiltrates. An improved disease-specific survival was evident for patients with high enrichment scores, and complete responses to anti-PD-1/PD-L1 treatment were observed in three of four cases with high enrichment scores. Thus, γδ T-cell infiltration may serve as a prognostic biomarker and should be explored for therapeutic interventions.See related Spotlight on p. 600.

Surgical Management of Merkel Cell Carcinoma

The incidence of Merkel cell carcinoma (MCC) continues to increase. Understanding of MCC biology has advanced rapidly, with current staging providing valuable prognostic information. MCC treatment often is multidisciplinary. Surgery remains an important component in the staging and treatment, most commonly involving wide excision of the cancer and sentinel lymph node biopsy. Lymphadenectomy is used to treat nodal disease. Radiotherapy enhances locoregional control and possibly survival. Systemic therapies, in particular novel immunotherapies, may be promising in the treatment of advanced or recurrent and metastatic disease.

Virus-positive Merkel Cell Carcinoma Is an Independent Prognostic Group with Distinct Predictive Biomarkers

PURPOSE

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine carcinoma that can be divided into two classes: virus-positive (VP) MCC, associated with oncogenic Merkel cell polyomavirus (MCPyV); and virus-negative (VN) MCC, associated with photodamage.

EXPERIMENTAL DESIGN

We classified 346 MCC tumors from 300 patients for MCPyV using a combination of IHC, ISH, and qPCR assays. In a subset of tumors, we profiled mutation status and expression of cancer-relevant genes. MCPyV and molecular profiling results were correlated with disease-specific outcomes. Potential prognostic biomarkers were further validated by IHC.

RESULTS

A total of 177 tumors were classified as VP-MCC, 151 tumors were VN-MCC, and 17 tumors were indeterminate. MCPyV positivity in primary tumors was associated with longer disease-specific and recurrence-free survival in univariate analysis, and in multivariate analysis incorporating age, sex, immune status, and stage at presentation. Prioritized oncogene or tumor suppressor mutations were frequent in VN-MCC but rare in VP-MCC. TP53 mutation developed with recurrence in one VP-MCC case. Importantly, for the first time we find that VP-MCC and VN-MCC display distinct sets of prognostic molecular biomarkers. For VP-MCC, shorter survival was associated with decreased expression of immune markers including granzyme and IDO1. For VN-MCC, shorter survival correlated with high expression of several genes including UBE2C.

CONCLUSIONS

MCPyV status is an independent prognostic factor for MCC. Features of the tumor genome, transcriptome, and microenvironment may modify prognosis in a manner specific to viral status. MCPyV status has clinicopathologic significance and allows for identification of additional prognostic subgroups.

Merkel cell carcinoma-derived exosome-shuttle miR-375 induces fibroblast polarization by inhibition of RBPJ and p53

Merkel cell carcinoma (MCC) is a highly invasive and metastatic skin cancer. While high expression of miR-375 is a characteristic of MCC, it seems not to contribute to the malignant phenotype of MCC cells. miR-375 enrichment in MCC-derived extracellular vesicles suggests its intercellular signaling function. Here, we demonstrate that horizontally transferred miR-375 causes fibroblast polarization toward cancer-associated fibroblasts (CAFs). The polarization is evidenced by phenotypic changes and induction of α-SMA, CXCL2, and IL-1β. Fibroblast polarization is inhibited by specific antagomirs and mimicked by experimental miR-375 expression. Mechanistically, miR-375 downregulates RBPJ and p53, two key players regulating fibroblast polarization. In clinical MCC samples, in situ hybridization located miR-375 in CAFs, which correlated with high α-SMA protein and low RBPJ and TP53 expression; single-cell RNAseq revealed a disparate fibroblast polarization negatively correlating with p53 pathway-related gene expression. Thus, the functional role of miR-375 in MCC is to generate a pro-tumorigenic microenvironment by inducing fibroblast polarization.

Tumor infiltrating lymphocyte grade in Merkel cell carcinoma: relationships with clinical factors and independent prognostic value

INTRODUCTION

Surrogate markers of the host immune response are not currently included in AJCC staging for Merkel cell carcinoma (MCC), and have not been consistently associated with clinical outcomes. We performed an analysis of a large national database to investigate tumor infiltrating lymphocyte (TIL) grade as an independent predictor of overall survival (OS) for patients with MCC and to characterize the relationship between TIL grade and other clinical prognostic factors.

MATERIAL AND METHODS

The NCDB was queried for patients with resected, non-metastatic MCC with known TIL grade (absent, non-brisk and brisk). Multivariable Cox regression modeling was performed to define TIL grade as a predictor of OS adjusting for other relevant clinical factors. Multinomial, multivariable logistic regression was performed to characterize the relationship between TIL grade and other clinical prognostic factors. Multiple imputation was performed to account for missing data bias.

RESULTS

Both brisk (HR 0.55, CI 0.36-0.83) and non-brisk (HR 0.77, CI 0.60-0.98) were associated with decreased adjusted hazard of death relative to absent TIL grade. Adverse clinical factors such as 1-3 positive lymph nodes, lymphovascular invasion (LVI) and immunosuppression were associated with increased likelihood of non-brisk TIL relative to absent TIL grade (p values <.05). Extracapsular extension (ECS) was associated with decreased likelihood of brisk TIL relative to absent TIL grade (p<.05).

DISCUSSION

Histopathologic TIL grade was independently predictive for OS in this large national cohort. Significant differences in the likelihood of non-brisk or brisk TIL relative to absent grade were present with regards to LVI, ECS and immune status. TIL grade may be a useful prognostic factor to consider in addition to more granular characterization of TIL morphology and immunophenotype.

Pembrolizumab and other immune checkpoint inhibitors in locally advanced or metastatic Merkel Cell Carcinoma: safety and efficacy

INTRODUCTION

Merkel Cell Carcinoma (MCC) is a rare aggressive skin cancer, mostly affecting elderly patients. Until recently, patients with advanced disease were treated with cytotoxic chemotherapies despite rapid chemoresistance and high toxicity. As with other cancers, immune checkpoint inhibitors (CPI), including pembrolizumab, allow durable responses with a manageable safety profile in these patients.

AREAS COVERED

This review describes the rationale for using PD-1/PD-L1 inhibitors in MCC, as well as efficacy and safety results from the three open-label trials investigating pembrolizumab or other PD-1/PD-L1 inhibitors in patients with advanced MCC. Real-life experience and predictive pre-treatment biomarkers are discussed to assess which patients are likely to be candidates for such strategies. Ongoing fields of research include the use of CPI in the adjuvant or neoadjuvant setting and combined strategies in refractory patients. Expert Opinion: CPI have become the standard of care for frontline treatment in patients with advanced MCC. Earlier introduction of CPI in the disease course, including neo-adjuvant and adjuvant settings, is likely to improve the outcomes further. Given the rarity of this cancer, we still need to harmonize efforts in order to conduct large-scale trials and efficiently identify best optimal care.

T-Cell Repertoire in Combination with T-Cell Density Predicts Clinical Outcomes in Patients with Merkel Cell Carcinoma

The integrity of the immune system represents a pivotal risk factor and prognostic biomarker for Merkel cell carcinoma. A higher density of tumor-associated T cells correlates with improved Merkel cell carcinoma-specific survival, but the prognostic importance of the T-cell infiltrate reactivity is unknown. We evaluated the T-cell receptor repertoire associated with 72 primary Merkel cell carcinomas and correlated metrics of the T-cell receptor repertoire with clinicopathologic characteristics and patient outcomes. We showed that a high Simpson's Dominance index (SDom) was significantly associated with fewer metastases (P = 0.01), lower stage at presentation (P = 0.02), lower final stage at last follow-up (P = 0.05), and longer time to first lymph node metastasis (P = 0.04). These correlations were mostly preserved in the Merkel cell polyomavirus-negative subgroup. Combining SDom with CD3⁺ or CD8⁺ T-cell density revealed three distinct prognostic groups with respect to disease-specific survival. Patients with both high SDom and high CD3⁺ or CD8⁺ T-cell density had markedly improved disease-specific survival compared with patients with low SDom and low CD3⁺ or CD8⁺ T-cell density (P = 0.002 and P = 0.03, respectively). Patients with either high SDom or high CD3⁺ or CD8⁺ had intermediate disease-specific survival. Our findings demonstrate that the quality of the tumor-associated T-cell infiltrate informs patient prognosis in primary Merkel cell carcinoma beyond the T-cell density.

Immunobiology of Merkel cell carcinoma

PURPOSE OF REVIEW

Merkel cell carcinoma (MCC) is a rare and aggressive skin cancer, which is associated in 80% of cases with the Merkel cell polyomavirus (MCPyV). Advanced stages respond to immune checkpoint inhibitors in 50% of cases. Major issues remain unanswered regarding its oncogenesis and optimal treatment.

RECENT FINDINGS

MCPyV-negative and MCPyV-positive MCCs have been hypothesized to derive from distinct cells, although the cell of origin remains a matter of debate. The crucial role the MCPyV small T oncoprotein was recently confirmed by its ability to inactivate p53, together with its contribution to the metastatic progression. In advanced cases, tumoral microenvironment may adequately predict responses to immunotherapies, and several mechanisms of primary and secondary resistance have been investigated.

SUMMARY

Identifying the mechanisms of oncogenesis allow experimentation of new therapeutic targets, which remain mandatory even at the era of immunotherapies. Although new insights in the mechanisms of primary and secondary resistance pave the way for development of further immunotherapy strategies, neoadjuvant strategies may challenge our whole approach of the disease.

Impact of Tumor-Infiltrating Lymphocytes on Overall Survival in Merkel Cell Carcinoma

BACKGROUND

Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine carcinoma of the skin. As the clinical course can be variable, prognostic markers are needed to better stratify patients. Prior literature, composed of small series with limited sample size, has demonstrated that tumor-infiltrating lymphocytes (TILs) are an important prognostic marker in MCC. To validate these findings on a population level, we sought to analyze and report the prognostic value of TILs in a large national data set.

MATERIALS AND METHODS

A retrospective observational cohort study was conducted of patients with nonmetastatic MCC from 2010 to 2015 using the National Cancer Database. Individual variables trending toward significance using a univariable analysis were included in a multivariable Cox proportional hazards model to assess their independent effect on overall survival (OS). TILs were subclassified into none, nonbrisk, and brisk and the survival analysis was performed. Propensity score-weighted multivariable analysis (PS MVA) was performed to adjust for additional confounding.

RESULTS

A total of 2,182 patients met inclusion criteria: 611 (28.0%) were identified as having TILs present, and 1,571 (72.0%) had TILs absent in the tumor. On MVA, subdivision of TIL status into nonbrisk (hazard ratio [HR], 0.750; 95% confidence interval [CI], 0.602-0.933) and brisk (HR, 0.499; 95% CI, 0.338-0.735) was associated with incrementally improved OS compared with no TILs. The association of nonbrisk and brisk TILs with improved OS was retained on PS MVA (Nonbrisk: HR, 0.720; 95% CI, 0.550-0.944; Brisk: HR, 0.483; 95% CI, 0.286-0.814).

CONCLUSION

The presence of nonbrisk and brisk TILs is associated with incrementally improved OS in patients with nonmetastatic MCC in a large national data set. This pathologic feature can aid with risk stratification, estimation of prognosis, and, importantly, decision-making with respect to treatment intensification in high-risk patients.

IMPLICATIONS FOR PRACTICE

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine cutaneous malignancy with variable clinical course. Prognostic markers are needed to better risk stratify patients. We present the largest retrospective observational cohort study of patients with nonmetastatic MCC using the National Cancer Database. Our analysis demonstrates an association between increasing degrees of tumor-infiltrating lymphocytes and incrementally improved survival. These conclusions improve pathologic risk stratification, and decision-making with respect to treatment intensification. Intensification may include adjuvant radiation therapy to the primary site after wide excision despite small tumor size, to the nodal basin in sentinel lymph node-negative patients, or offering closer follow-up.

Real-world outcomes among US Merkel cell carcinoma patients initiating immune checkpoint inhibitors or chemotherapy

Aim: Retrospectively assessed treatment patterns and clinical and economic outcomes in Merkel cell carcinoma (MCC) patients receiving recommended first-line regimens. Materials & methods: MCC patients newly treated with either immune checkpoint inhibitors (ICIs) or chemotherapies (CTs) were selected from the Veterans Health Administration database (2013-2018); 74 patients (ICIs: 20 and CTs: 54) were selected. Results: Median duration of therapy was 300 days for ICIs and 91 days for CTs. Time to next treatment was 245 and 184 days, respectively. Mean total (per patient per month) costs were $15,306 (ICIs) and $10,957 (CTs), of which 51% and 86%, respectively, were non-MCC therapy-related costs. Conclusion: Despite higher costs, utilization of ICIs in first-line MCC shows clinical advantages over CTs in the real world.

Polyomavirus-driven Merkel cell carcinoma: Prospects for therapeutic vaccine development

Great strides have been made in cancer immunotherapy including the breakthrough successes of anti-PD-(L)1 checkpoint inhibitors. In Merkel cell carcinoma (MCC), a rare and aggressive skin cancer, PD-(L)1 blockade is highly effective. Yet, ~50% of patients either do not respond to therapy or develop PD-(L)1 refractory disease and, thus, do not experience long-term benefit. For these patients, additional or combination therapies are needed to augment immune responses that target and eliminate cancer cells. Therapeutic vaccines targeting tumor-associated antigens, mutated self-antigens, or immunogenic viral oncoproteins are currently being developed to augment T-cell responses. Approximately 80% of MCC cases in the United States are driven by the ongoing expression of viral T-antigen (T-Ag) oncoproteins from genomically integrated Merkel cell polyomavirus (MCPyV). Since T-Ag elicits specific B- and T-cell immune responses in most persons with virus-positive MCC (VP-MCC), and ongoing T-Ag expression is required to drive VP-MCC cell proliferation, therapeutic vaccination with T-Ag is a rational potential component of immunotherapy. Failure of the endogenous T-cell response to clear VP-MCC (allowing clinically evident tumors to arise) implies that therapeutic vaccination will need to be potent anśd synergize with other mechanisms to enhance T-cell activity against tumor cells. Here, we review the relevant underlying biology of VP-MCC, potentially applicable therapeutic vaccine platforms, and antigen delivery formats. We also describe early successes in the field of therapeutic cancer vaccines and address several clinical scenarios in which VP-MCC patients could potentially benefit from a therapeutic vaccine.

Inhibition of PI3K by copanlisib exerts potent antitumor effects on Merkel cell carcinoma cell lines and mouse xenografts

Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine skin cancer with steadily increasing incidence and poor prognosis. Despite recent success with immunotherapy, 50% of patients still succumb to their diseases. To date, there is no Food and Drug Administration-approved targeted therapy for advanced MCC. Aberrant activation of phosphatidylinositide-3-kinase (PI3K)/AKT/mTOR pathway is frequently detected in MCC, making it an attractive therapeutic target. We previously found PI3K pathway activation in human MCC cell lines and tumors and demonstrated complete clinical response in a Stage IV MCC patient treated with PI3K inhibitor idelalisib. Here, we found that both PI3K-α and -δ isoforms are abundantly expressed in our MCC cell lines and clinical samples; we therefore examined antitumor efficacy across a panel of five PI3K inhibitors with distinctive isoform-specificities, including idelalisib (PI3K-δ), copanlisib (PI3K-α/δ), duvelisib (PI3K-γ/δ), alpelisib (PI3K-α), and AZD8186 (PI3K-β/δ). Of these, copanlisib exerts the most potent antitumor effects, markedly inhibiting cell proliferation, survival, and tumor growth by suppressing PI3K/mTOR/Akt activities in mouse models generated from MCC cell xenografts and patient-derived tumor xenografts. These results provide compelling preclinical evidence for application of copanlisib in advanced MCC with aberrant PI3K activation for which immunotherapy is insufficient, or patients who are unsuitable for immunotherapy.

Selective reactivation of STING signaling to target Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a lethal skin cancer that metastasizes rapidly. Few effective treatments are available for patients with metastatic MCC. Poor intratumoral T cell infiltration and activation are major barriers that prevent MCC eradication by the immune system. However, the mechanisms that drive the immunologically restrictive tumor microenvironment remain poorly understood. In this study, we discovered that the innate immune regulator stimulator of IFN genes (STING) is completely silenced in MCCs. To reactivate STING in MCC, we developed an application of a human STING mutant, STING^{S162A/G230I/Q266I}, which we found to be readily stimulated by a mouse STING agonist, DMXAA. This STING molecule was efficiently delivered to MCC cells via an AAV vector. Introducing STING^{S162A/G230I/Q266I} expression and stimulating its activity by DMXAA in MCC cells reactivates their antitumor inflammatory cytokine/chemokine production. In response to MCC cells with restored STING, cocultured T cells expressing MCPyV-specific T cell receptors (TCRs) show increased cytokine production, migration toward tumor cells, and tumor cell killing. Our study therefore suggests that STING deficiency contributes to the immune suppressive nature of MCCs. More importantly, DMXAA stimulation of STING^{S162A/G230I/Q266I} causes robust cell death in MCCs as well as several other STING-silenced cancers. Because tumor antigens and DNA released by dying cancer cells have the potential to amplify innate immune response and activate antitumor adaptive responses, our finding indicates that targeted delivery and activation of STING^{S162A/G230I/Q266I} in tumor cells holds great therapeutic promise for the treatment of MCC and many other STING-deficient cancers.

Tumor Ulceration, Reduced Infiltration of CD8-Lymphocytes, High Neutrophil-to-CD8-Lymphocyte Ratio and Absence of MC Virus are Negative Prognostic Markers for Patients with Merkel Cell Carcinoma

(1) Background: Merkel cell carcinoma (MCC) is caused by the Merkel cell polyomavirus and UV radiation. Understanding of the underlying biology is limited, but identification of prognostic markers may lead to better prognostic stratification for the patients. (2) Methods: Ninety patients diagnosed with MCC (1996–2012) were included. Virus status was estimated by polymerase chain reaction (qPCR) and immunohistochemistry (IHC). Ulceration status, PD-L1, cd66b neutrophils, cd8 lymphocytes and biomarkers of vascularization (cd34 endothelial cells) and migration (e-cadherin) were estimated by IHC and analyzed with digital pathology. (3) Results: Virus was present in 47% of patient samples and correlated with lower E-cadherin expression (p = 0.0005), lower neutrophil-to-CD8 lymphocyte ratio (N:CD8 ratio) (p = 0.02) and increased PD-L1 expression (p = 0.03). Ulceration was associated with absence of virus (p = 0.03), increased neutrophil infiltration (p < 0.0001) and reduced CD8 lymphocyte infiltration (p = 0.04). In multivariate analysis, presence of virus (p = 0.01), ulceration (p = 0.05) and increased CD8 lymphocyte infiltration (p = 0.001) showed independent prognostic impacts on MCC-specific survival. (3) Conclusions: In this study, we found that a high N:CD8 ratio, ulceration, virus-negative status and absence of CD8 lymphocytes are negative prognostic markers. Accurate prognostic stratification of the patients may be important in the clinical setting for determination of adjuvant treatment.

PD-L1 Detection-Pearls and Pitfalls Associated With Current Methodologies Focusing on Entities Relevant to Dermatopathology

PD-L1 is a transmembrane glycoprotein with an extracellular as well as an intracellular cytoplasmic domain. Physiologically, it plays a pivotal role in regulating T-cell activation and tolerance. Many tumor cells have exploited this regulatory mechanism by overexpressing PD-L1 in an effort to escape immunologic surveillance. In this review, we parse the literature regarding the prognostic value of tumoral PD-L1 expression before discussing the various methodologies as well as the pearls and pitfalls associated with each for predicting response to anti-PD-1/PD-L1 therapies. Special attention is given to cutaneous entities in which PD-L1 expression has been documented with an emphasis on cutaneous malignancies that have seen the broadest applications of anti-PD-L1/PD-1 therapies. Currently, immunohistochemistry is the method that is most commonly used for detection of PD-L1. However, with the wide array of immunohistochemistry protocols and staining platforms available in the market, there seems to be different cutoffs not just for different entities but also for the same entity. This review is an attempt to address the need for standardization and validation of existing protocols for PD-L1 detection.

Combined radio-immunotherapy leads to complete clinical regression of stage IV Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare, aggressive neuroendocrine tumour of the skin. While localised disease carries an overall favourable prognosis, metastatic disease is associated with poor clincal outcomes. Most cases of metastatic MCC are managed with systemic chemotherapy or immunotherapy, though 5-year survival for these patients remains a dismal 17%. Here, we present the case of a 79-year-old man with MCC of the right ear with metastases to regional lymph nodes, ipsilateral parotid gland and thoracic spine. He was treated with a combination of first-line radiotherapy and concurrent immune checkpoint inhibition (avelumab), which led to complete clinical regression of disease with minimal adverse effects. This observation suggests that combined radio-immunotherapy warrants larger-scale investigation for use in patients with unresectable MCC.

Human CD4+ T Cells Specific for Merkel Cell Polyomavirus Localize to Merkel Cell Carcinomas and Target a Required Oncogenic Domain

Although CD4⁺ T cells likely play key roles in antitumor immune responses, most immuno-oncology studies have been limited to CD8⁺ T-cell responses due to multiple technical barriers and a lack of shared antigens across patients. Merkel cell carcinoma (MCC) is an aggressive skin cancer caused by Merkel cell polyomavirus (MCPyV) oncoproteins in 80% of cases. Because MCPyV oncoproteins are shared across most patients with MCC, it is unusually feasible to identify, characterize, and potentially augment tumor-specific CD4⁺ T cells. Here, we report the identification of CD4⁺ T-cell responses against six MCPyV epitopes, one of which included a conserved, essential viral oncogenic domain that binds/disables the cellular retinoblastoma (Rb) tumor suppressor. We found that this epitope (WED_LT209-228) could be presented by three population-prevalent HLA class II alleles, making it a relevant target in 64% of virus-positive MCC patients. Cellular staining with a WED_LT209-228-HLA-DRB1*0401 tetramer indicated that specific CD4⁺ T cells were detectable in 78% (14 of 18) of evaluable MCC patients, were 250-fold enriched within MCC tumors relative to peripheral blood, and had diverse T-cell receptor sequences. We also identified a modification of this domain that still allowed recognition by these CD4⁺ T cells but disabled binding to the Rb tumor suppressor, a key step in the detoxification of a possible therapeutic vaccine. The use of these new tools for deeper study of MCPyV-specific CD4⁺ T cells may provide broader insight into cancer-specific CD4⁺ T-cell responses.

Viral and tumor antigen-specific CD8 T-cell responses in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare and aggressive cutaneous cancer, which is immunogenic, regardless of the presence of MCPyV (80% of cases). The identification of MCC-specific epitopes recognized by CD8 T cells is crucial to expand the arsenal of immunotherapeutic treatments. Until now, most efforts focused on the identification of virus-specific epitopes, whereas immune responses directed against shared cellular tumor-specific antigens have not been evidenced. In this study, we measured T-cell responses against viral (n = 3) and tumor antigens (n = 47) from TILs derived from 21 MCC tumors. Virus-specific CD8 T-cell responses dominated MCC-specific immune responses, and we identified two new HLA-peptide complexes derived from the LT antigen, located in a region encompassing 3 previously identified epitopes. Finally, we show that MAGE-A3 antigen, frequently expressed by MCC tumors, was recognized by CD8 TILs from a virus-negative MCC tumor and thus could be a target for immunotherapy in this setting.

Complete response with neoadjuvant avelumab in Merkel cell carcinoma - A case report

Merkel cell carcinoma (MCC) is a rare but aggressive neuroendocrine skin malignancy. We report here a case of localized MCC achieving pathologic complete response upon treatment with avelumab in the neoadjuvant setting. Preclinical and clinical studies have revealed a close relationship between MCC and the immune system, thus supporting a role for PD-1/PD-L1 inhibitors in MCC. This neoadjuvant use of PD-1/PD-L1 inhibitors can avoid potentially disfiguring surgery in MCC. As the incidence of MCC is rising, clinical trials are needed to evaluate the efficacy and safety of immunotherapy in resectable disease.