Immune Checkpoint Inhibitors and Beyond: An Overview of Immune-Based Therapies in Merkel Cell Carcinoma

The prognostic role of PD-L1 expression and the presence of polyomavirus in Merkel cell carcinoma cases

BACKGROUND

Merkel cell carcinoma (MCC) comprises a rare malignant primary skin tumor presenting neuroendocrine differentiation. Recently, agents blocking the programmed cell death protein 1 and programmed cell death protein ligand 1 pathway (PD-1/PD-L1) have demonstrated objective and durable tumor regressions in patients presenting advanced MCC. This study aimed to describe the sociodemographic, clinical, and histopathological characteristics of MCC patients, also assessing the prevalence of PD-L1 expression and Merkel cell Polyomavirus (MCPyV), as well as their prognostic roles.

METHODS

Data from patients diagnosed with MCC between 1996 and 2019 at a reference cancer center in Rio de Janeiro, southeastern Brazil, were evaluated in a retrospective study. Tumor samples were tested for MCPyV and PD-L1 employing immunohistochemistry. Survival analyses were carried out employing the Kaplan-Meier method and curves were compared using the log-rank test. A multiple semiparametric Cox model was used. Values p < 0.05 were considered significant.

RESULTS

A total of 65 patients were included in the study, with a mean age at diagnosis of 72 (standard deviation 13.9). A total of 56.9% (37/65) of the patients were male, 86.2% (56/65) were white, and 56.9% (37/64) were illiterate or with incomplete elementary school. MCPyV immunohistochemistry was positive in 29 cases (44.6%) and PD-L1 positivity was ≥ 1% in 42 cases (64.6%). Significant associations between MCPyV and PD-L1 expression ≥ 1% (p = 0.003) and PD-L1 expression ≥ 5% (p = 0.005) were noted. Concerning the multivariate analysis, only education level and advanced MCC stage indicated statistically significant worse progression-free survival. Regarding overall survival (OS), being male, education level and advanced stage comprised risk factors. The estimated OS at 60 months for stages I to III was of 48.9% and for stage IV, 8.9%.

CONCLUSIONS

This is the first large Brazilian cohort to assess the prevalence of MCPyV in MCC tumors, as well as PD-L1 expression and their associations. No correlations were noted between MCPyV infection or PD-L1 expression and survival rates.

Dissecting the tumour immune microenvironment in merkel cell carcinoma based on a machine learning framework

Merkel cell carcinoma (MCC) is a primary cutaneous neoplasm of neuroendocrine carcinoma of the skin, which is characterized by molecular heterogeneity with diverse tumour microenvironment (TME). However, we are still lack knowledge of the cellular states and ecosystems in MCC. Here, we systematically identified and characterized the landscape of cellular states and ecotypes in MCC based on a machine learning framework. We obtained 30 distinct cellular states from 9 immune cell types and investigated the B cell, CD8 T cell, fibroblast, and monocytes/macrophage cellular states in detail. The functional profiling of cellular states were investigated and found the genes highly expressed in cellular states were significantly enriched in immune- and cancer hallmark-related pathways. In addition, four ecotypes were further identified which were with different patient compositions. Transcriptional regulation analysis revealed the critical transcription factors (i.e. E2F1, E2F3 and E2F7), which play important roles in regulating the TME of MCC. In summary, the findings of this study may provide rich knowledge to understand the intrinsic subtypes of MCCs and the pathways involved in distinct subtype oncogenesis, and will further advance the knowledge in developing a specific therapeutic strategy for these MCC subtypes.

Oncoviruses: How do they hijack their host and current treatment regimes

Viruses have the ability to modulate the cellular machinery of their host to ensure their survival. While humans encounter numerous viruses daily, only a select few can lead to disease progression. Some of these viruses can amplify cancer-related traits, particularly when coupled with factors like immunosuppression and co-carcinogens. The global burden of cancer development resulting from viral infections is approximately 12%, and it arises as an unfortunate consequence of persistent infections that cause chronic inflammation, genomic instability from viral genome integration, and dysregulation of tumor suppressor genes and host oncogenes involved in normal cell growth. This review provides an in-depth discussion of oncoviruses and their strategies for hijacking the host's cellular machinery to induce cancer. It delves into how viral oncogenes drive tumorigenesis by targeting key cell signaling pathways. Additionally, the review discusses current therapeutic approaches that have been approved or are undergoing clinical trials to combat malignancies induced by oncoviruses. Understanding the intricate interactions between viruses and host cells can lead to the development of more effective treatments for virus-induced cancers.

An Investigation of Structure-Activity Relationships and Cell Death Mechanisms of the Marine Alkaloids Discorhabdins in Merkel Cell Carcinoma Cells

A library of naturally occurring and semi-synthetic discorhabdins was assessed for their effects on Merkel cell carcinoma (MCC) cell viability. The set included five new natural products and semi-synthetic compounds whose structures were elucidated with NMR, HRMS, and ECD techniques. Several discorhabdins averaged sub-micromolar potency against the MCC cell lines tested and most of the active compounds showed selectivity towards virus-positive MCC cell lines. An investigation of structure-activity relationships resulted in an expanded understanding of the crucial structural features of the discorhabdin scaffold. Mechanistic cell death assays suggested that discorhabdins, unlike many other MCC-active small molecules, do not induce apoptosis, as shown by the lack of caspase activation, annexin V staining, and response to caspase inhibition. Similarly, discorhabdin treatment failed to increase MCC intracellular calcium and ROS levels. In contrast, the rapid loss of cellular reducing potential and mitochondrial membrane potential suggested that discorhabdins induce mitochondrial dysfunction leading to non-apoptotic cell death.

Merkel cell carcinoma: epidemiology, clinical features, diagnosis and treatment of a rare disease

Merkel cell carcinoma is a rare skin cancer with neuroendocrine differentiation. The risk factors include sun exposure, advanced age, immunosuppression (such as transplant recipients, patients with lymphoproliferative neoplasms, or patients with HIV), and Merkel cell polyomavirus infection. Clinically, Merkel cell carcinoma appears as a cutaneous or subcutaneous plaque or nodule, but this tumor diagnosis is rarely made clinically. Therefore, histopathology and immunohistochemistry are usually necessary. Primary tumors without evidence of metastases are treated with complete surgical excision and appropriate surgical margins. The presence of occult metastasis in a lymph node is frequent and a sentinel lymph node biopsy should be performed. Postoperative adjuvant radiotherapy increases local tumor control. Recently, agents that block the PD-1/PD-L1 pathway have shown objective and durable tumor regression in patients with advanced solid malignancies. The first anti-PD-L1 antibody used in patients with Merkel cell carcinoma was avelumab, but pembrolizumab and nivolumab have also shown efficacy. This article describes the current state of knowledge of the epidemiology, diagnosis, and staging of Merkel cell carcinoma, as well as new strategies for its systemic treatment.

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.

Society for Immunotherapy of Cancer (SITC) clinical practice guideline on immunotherapy for the treatment of nonmelanoma skin cancer

Nonmelanoma skin cancers (NMSCs) are some of the most commonly diagnosed malignancies. In general, early-stage NMSCs have favorable outcomes; however, a small subset of patients develop resistant, advanced, or metastatic disease, or aggressive subtypes that are more challenging to treat successfully. Recently, immune checkpoint inhibitors (ICIs) have been approved by the US Food and Drug Administration (FDA) for the treatment of Merkel cell carcinoma (MCC), cutaneous squamous cell carcinoma (CSCC), and basal cell carcinoma (BCC). Although ICIs have demonstrated activity against NMSCs, the routine clinical use of these agents may be more challenging due to a number of factors including the lack of predictive biomarkers, the need to consider special patient populations, the management of toxicity, and the assessment of atypical responses. With the goal of improving patient care by providing expert guidance to the oncology community, the Society for Immunotherapy of Cancer (SITC) convened a multidisciplinary panel of experts to develop a clinical practice guideline (CPG). The expert panel drew on the published literature as well as their own clinical experience to develop recommendations for healthcare professionals on important aspects of immunotherapeutic treatment for NMSCs, including staging, biomarker testing, patient selection, therapy selection, post-treatment response evaluation and surveillance, and patient quality of life (QOL) considerations, among others. The evidence- and consensus-based recommendations in this CPG are intended to provide guidance to cancer care professionals treating patients with NMSCs.

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.

The Role of Histone Post-Translational Modifications in Merkel Cell Carcinoma

Merkel Cell Carcinoma (MCC) is a rare but highly aggressive form of non–melanoma skin cancer whose 5-year survival rate is 63%. Merkel cell polyomavirus (MCPyV), a small DNA tumor virus, is the etiological agent of MCC. Although representing a small proportion of MCC cases, MCPyV-negative MCCs have also been identified. The role of epigenetic mechanisms, including histone post-translational modifications (PTMs) in MCC, have been only partially determined. This review aims to describe the most recent progress on PTMs and their regulative factors in the context of MCC onset/development, providing an overview of current findings on both MCC subtypes. An outline of current knowledge on the potential employment of PTMs and related factors as diagnostic and prognostic markers, as well as novel treatment strategies targeting the reversibility of PTMs for MCC therapy is provided. Recent research shows that PTMs are emerging as important epigenetic players involved in MCC onset/development, and therefore may show a potential clinical significance. Deeper and integrated knowledge of currently known PTM dysregulations is of paramount importance in order to understand the molecular basis of MCC and improve the diagnosis, prognosis, and therapeutic options for this deadly tumor.

Inhibition of T-antigen expression promoting glycogen synthase kinase 3 impairs merkel cell carcinoma cell growth

Merkel cell carcinoma is an aggressive skin cancer frequently caused by the Merkel cell polyomavirus (MCPyV). Since proliferation of MCPyV-positive MCC tumor cells strictly depends on expression of the virus-encoded T antigens (TA), these proteins theoretically represent ideal targets for different kinds of therapeutic approaches. Here we developed a cell-based assay to identify compounds which specifically inhibit growth of MCC cells by repressing TA expression. Applying this technique we screened a kinase inhibitor library and identified six compounds targeting glycogen synthase kinase 3 (GSK3) such as CHIR99021 as suppressors of TA transcription in MCC cells. Involvement of GSK3α and -β in the regulation of TA-expression was confirmed by combining GSK3A knockout with inducible GSK3B shRNA knockdown since double knockouts could not be generated. Finally, we demonstrate that CHIR99021 exhibits in vivo antitumor activity in an MCC xenograft mouse model suggesting GSK3 inhibitors as potential therapeutics for the treatment of MCC in the future.

Merkel Cell Polyomavirus Antibody Titer Predicts Recurrence-Free Survival

BACKGROUND

Merkel cell polyomavirus (MCPyV) is associated with the development of Merkel cell carcinoma (MCC). Antibody (MCPyV-Ab) titers may have prognostic implications. This study evaluated the impact of the presence or absence of MCPyV-Ab on the 2-year overall survival (OS) and disease-free survival (DFS) of MCC patients.

METHODS

This single-center, IRB-approved, retrospective cohort study evaluated 51 adult patients with MCC from 2014 to 2021 using a prospectively maintained database. Patients were compared by MCPyV-Ab status, and Kaplan-Meier analysis was used to evaluate 2-year OS and DFS.

RESULTS

Of the 51 patients, 13 (25.4%) were seropositive, 41 (80.4%) underwent wide excision, 40 (80.0%) received radiotherapy, and 43 (84.3%) received multimodal therapy. The median follow-up period was 15.5 months (range 1-69.5 months). The median 2-year OS of the entire cohort was not reached. The median 2-year OS was not reached for either the seronegative or the seropositive patients. The difference in 2-year OS between the groups was not statistically significant (p = 0.37). Eight patients, all seronegative, were never rendered disease-free and were removed from recurrence analysis. The seropositive patients experienced no recurrences. Of the 30 seronegative patients, 9 (30.0%) experienced recurrence. The median 2-year DFS of the entire cohort was not reached. The median 2-year DFS of the seronegative group was 22.2 months. The 2-year DFS was not reached for the seropositive cohort. Seropositivity conferred a significantly better 2-year DFS than seronegativity (p = 0.04).

CONCLUSION

The MCPyV-Ab seropositive patients demonstrated improved 2-year DFS. The seropositive patients showed a strong trend toward improved 2-year OS, although the difference not statistically significant. This study substantiated the value of MCPyV-Ab assessment for MCC.

Response durability after cessation of immune checkpoint inhibitors in patients with metastatic Merkel cell carcinoma: a retrospective multicenter DeCOG study

BACKGROUND

Immune checkpoint inhibitors (ICI) have led to a prolongation of progression-free and overall survival in patients with metastatic Merkel cell carcinoma (MCC). However, immune-mediated adverse events due to ICI therapy are common and often lead to treatment discontinuation. The response duration after cessation of ICI treatment is unknown. Hence, this study aimed to investigate the time to relapse after discontinuation of ICI in MCC patients.

METHODS

We analyzed 20 patients with metastatic MCC who have been retrospectively enrolled at eleven skin cancer centers in Germany. These patients have received ICI therapy and showed as best overall response (BOR) at least a stable disease (SD) upon ICI therapy. All patients have discontinued ICI therapy for other reasons than disease progression. Data on treatment duration, tumor response, treatment cessation, response durability, and tumor relapse were recorded.

RESULTS

Overall, 12 of 20 patients (60%) with MCC relapsed after discontinuation of ICI. The median response durability was 10.0 months. Complete response (CR) as BOR to ICI-treatment was observed in six patients, partial response (PR) in eleven, and SD in three patients. Disease progression was less frequent in patients with CR (2/6 patients relapsed) as compared to patients with PR (7/11) and SD (3/3), albeit the effect of initial BOR on the response durability was below statistical significance. The median duration of ICI therapy was 10.0 months. Our results did not show a correlation between treatment duration and the risk of relapse after treatment withdrawal. Major reasons for discontinuation of ICI therapy were CR (20%), adverse events (35%), fatigue (20%), or patient decision (25%). Discontinuation of ICI due to adverse events resulted in progressive disease (PD) in 71% of patients regardless of the initial response. A re-induction of ICI was initiated in 8 patients upon tumor progression. We observed a renewed tumor response in 4 of these 8 patients. Notably, all 4 patients showed an initial BOR of at least PR.

CONCLUSION

Our results from this contemporary cohort of patients with metastatic MCC indicate that MCC patients are at higher risk of relapse after discontinuation of ICI as compared to melanoma patients. Notably, the risk of disease progression after discontinuation of ICI treatment is lower in patients with initial CR (33%) as compared to patients with initial PR (66%) or SD (100%). Upon tumor progression, re-induction of ICI is a feasible option. Our data suggest that the BOR to initial ICI therapy might be a potential predictive clinical marker for a successful re-induction.

Decreased IgG Antibody Response to Viral Protein Mimotopes of Oncogenic Merkel Cell Polyomavirus in Sera From Healthy Elderly Subjects

Merkel cell polyomavirus (MCPyV) is the main causative agent of Merkel cell carcinoma (MCC), a rare but aggressive skin tumor with a typical presentation age >60 years. MCPyV is ubiquitous in humans. After an early-age primary infection, MCPyV establishes a clinically asymptomatic lifelong infection. In immunocompromised patients/individuals, including elders, MCC can arise following an increase in MCPyV replication events. Elders are prone to develop immunesenescence and therefore represent an important group to investigate. In addition, detailed information on MCPyV serology in elders has been debated. These findings cumulatively indicate the need for new research verifying the impact of MCPyV infection in elderly subjects (ES). Herein, sera from 226 ES, aged 66-100 years, were analyzed for anti-MCPyV IgGs with an indirect ELISA using peptides mimicking epitopes from the MCPyV capsid proteins VP1-2. Immunological data from sera belonging to a cohort of healthy subjects (HS) (n = 548) aged 18-65 years, reported in our previous study, were also included for comparisons. Age-/gender-specific seroprevalence and serological profiles were investigated. MCPyV seroprevalence in ES was 63.7% (144/226). Age-specific MCPyV seroprevalence resulted as 62.5% (25/40), 71.7% (33/46), 64.9% (37/57), 63.8% (30/47), and 52.8% (19/36) in ES aged 66-70, 71-75, 76-80, 81-85, and 86-100 years, respectively (p > 0.05). MCPyV seroprevalence was 67% (71/106) and 61% (73/120) in ES males and females, respectively (p > 0.05). Lack of age-/gender-related variations in terms of MCPyV serological profiles was found in ES (p > 0.05). Notably, serological profile analyses indicated lower optical densities (ODs) in ES compared with HS (p < 0.05), while lower ODs were also determined in ES males compared with HS males (p < 0.05). Our data cumulatively suggest that oncogenic MCPyV circulates in elders asymptomatically at a relatively high prevalence, while immunesenescence might be responsible for a decreased IgG antibody response to MCPyV, thereby potentially leading to an increase in MCPyV replication levels. In the worse scenario, alongside other factors, MCPyV might drive MCC carcinogenesis, as described in elders with over 60 years of age.

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.

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.

Identification of natural product modulators of Merkel cell carcinoma cell growth and survival

Merkel cell carcinoma (MCC) is a rare, but aggressive skin cancer the incidence of which has increased significantly in recent years. The majority of MCCs have incorporated Merkel cell polyomavirus (VP-MCC) while the remainder are virus-negative (VN-MCC). Although a variety of therapeutic options have shown promise in treating MCC, there remains a need for additional therapeutics as well as probes for better understanding MCC. A high-throughput screening campaign was used to assess the ability of > 25,000 synthetic and natural product compounds as well as > 20,000 natural product extracts to affect growth and survival of VN-MCC and VP-MCC cell lines. Sixteen active compounds were identified that have mechanisms of action reported in the literature along with a number of compounds with unknown mechanisms. Screening results with pure compounds suggest a range of potential targets for MCC including DNA damage, inhibition of DNA or protein synthesis, reactive oxygen species, and proteasome inhibition as well as NFκB inhibition while also suggesting the importance of zinc and/or copper binding. Many of the active compounds, particularly some of the natural products, have multiple reported targets suggesting that this strategy might be a particularly fruitful approach. Processing of several active natural product extracts resulted in the identification of additional MCC-active compounds. Based on these results, further investigations focused on natural products sources, particularly of fungal origin, are expected to yield further potentially useful modulators of MCC.

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.

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.

Immunotherapy for Merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive form of skin cancer which, while chemosensitive, has high rates of relapse and chemoresistance, limiting the impact of chemotherapy. An immunogenic tumor, the management of advanced MCC has changed dramatically with the introduction of checkpoint inhibitors. This review will focus on the impact of immunotherapy in unresectable and metastatic MCC, ongoing research in the adjuvant and neoadjuvant settings, and future directions of immune-based strategies for this challenging cancer.

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.

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.

Complete response to avelumab and IL-15 superagonist N-803 with Abraxane in Merkel cell carcinoma: a case study

Merkel cell carcinoma (MCC) is a rare aggressive form of skin cancer originating in neuroendocrine cells. The antiprogrammed death ligand 1 (PD-L1) monoclonal antibody (mAb) avelumab has been approved for treatment of MCC, but options are limited, should it be ineffective as a monotherapy. Combined therapy with low/moderate dose nab-paclitaxel and an interleukin 15 (IL-15)-based therapeutic such as the IL-15 ‘superagonist’ N-803 may increase response by activation of the immune system. The case of a 71-year-old man diagnosed with MCC who achieved and maintained a complete response (CR) by treatment with the anti-PD-L1 mAb avelumab in combination with IL-15 superagonist N-803 and nab-paclitaxel (Abraxane) is presented. Avelumab treatment alone resulted in a response in a para-aortic lesion, but not the other tumor masses. N-803 was added, followed by nab-paclitaxel; CT showed a decrease in the size of the abdominal mass at 1 month, near resolution at 3 months and CR at 5 months. Abraxane was discontinued after the first CR on CT, and the patient continues on avelumab/N-803 treatment and maintains a CR. Combination of avelumab with low/moderate-dose chemotherapy and an immune enhancer such as N-803 may offer a viable treatment option for MCC patients for whom avelumab therapy alone was not effective.

Somatostatin Receptors in Merkel-Cell Carcinoma: A Therapeutic Opportunity Using Somatostatin Analog Alone or in Association With Checkpoint Inhibitors Immunotherapy. A Case Report

Background: Merkel-cell carcinoma (MCC) is a rare, highly aggressive skin cancer typically involving elderly people. Surgery is usually the first treatment for primary tumor. In adjuvant setting, radiotherapy is effective in reducing local recurrence and in improving overall survival. Regarding advanced disease, systemic chemotherapy ended up disappointing results whereas antiPD1/antiPD-L1 immunotherapy recently gave relevant clinical benefits. Interestingly, about the half of MCC patients expresses high somatostatin receptors (SRs) to possibly represent a target for the therapeutic use of somatostatin analogs (SSAs). Nevertheless, SSAs have been little studied in MCC and cases treated with SSAs in association with checkpoint inhibitor immunotherapy have not been published yet.

Case Report: We report the case of a 73-year-old man affected by metastatic MCC of right arm previously treated with surgery and adjuvant radio and chemotherapy. Three years later the patient presented loco-regional relapse involving lateral-cervical, mediastinal, and submandibular lymph nodes with high value of chromogranin A and neuron specific enolase. Due to the high expression of SRs at octreoscan and immunoistochemistry, patient started octreotide 30 mg i.m. every 28 days with a good control of disease for about 2 years. A widespread progression of disease was reported afterwards. The patient started the antiPD-L1 avelumab immunotherapy, only recently available in Italy, while still taking SSA. The patient showed an impressive regression of the disease after only four cycles of avelumab until complete remission.

Conclusions: SSA could be a valid therapeutic option in patients with MCC with high SR expression. When combined with PD-1/PD-L1 immune-checkpoint inhibition, SSA is likely to enhance antiproliferative activity. Our case report provides the rationale to conduct a prospective trial and translational research to verify the efficacy and safety of combined SSA and checkpoint inhibitors for advanced MCC.

Clinical Relevance of Liquid Biopsy in Melanoma and Merkel Cell Carcinoma

Melanoma and Merkel cell carcinoma are two aggressive skin malignancies with high disease-related mortality and increasing incidence rates. Currently, invasive tumor tissue biopsy is the gold standard for their diagnosis, and no reliable easily accessible biomarker is available to monitor patients with melanoma or Merkel cell carcinoma during the disease course. In these last years, liquid biopsy has emerged as a candidate approach to overcome this limit and to identify biomarkers for early cancer diagnosis, prognosis, therapeutic response prediction, and patient follow-up. Liquid biopsy is a blood-based non-invasive procedure that allows the sequential analysis of circulating tumor cells, circulating cell-free and tumor DNA, and extracellular vesicles. These innovative biosources show similar features as the primary tumor from where they originated and represent an alternative to invasive solid tumor biopsy. In this review, the biology and technical challenges linked to the detection and analysis of the different circulating candidate biomarkers for melanoma and Merkel cell carcinoma are discussed as well as their clinical relevance.

Circulating Tumor Cell Detection and Polyomavirus Status in Merkel Cell Carcinoma

The incidence of Merkel cell carcinoma (MCC), a rare and highly metastatic skin malignancy, has sharply increased in the last decade. Clinical biomarkers are urgently needed for MCC prognosis, treatment response monitoring, and early diagnosis of relapse. The clinical interest of circulating tumors cells (CTCs) has been validated in many solid cancers. The aim of this study was to compare CTC detection and characterization in blood samples of patients with MCC using the CellSearch System and the RosetteSep -DEPArray workflow, an innovative procedure to enrich, detect and isolate single CTCs. In preliminary experiments (using spiked MCC cell lines) both methods allowed detecting very few MCC cells. In blood samples from 19 patients with MCC at different stages, CellSearch detected MCC CTCs in 26% of patients, and the R-D workflow in 42% of patients. The detection of CTC-positive patients increased to 52% by the cumulative positivity rate of both methodologies. Moreover, Merkel cell polyomavirus DNA, involved in MCC oncogenesis, was detected in tumor biopsies, but not in all single CTCs from the same patient, reflecting the tumor heterogeneity. Our data demonstrate the possibility to detect, isolate and characterize CTCs in patients with MCC using two complementary approaches.

Recent advances in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine skin cancer that has been historically associated with limited treatment options and poor prognosis. In the past 10 years, research in MCC has progressed significantly, demonstrating improved outcomes when treating with immunotherapy, particularly PD-1/PD-L1 inhibitors, when compared with conventional chemotherapy. There is also increasing evidence of the abscopal effect, a phenomenon describing the regression of untreated, distant MCC tumors following local radiation therapy. Additionally, antibodies to Merkel cell polyomavirus oncoproteins have been found to correlate with disease burden in a subset of patients, providing a useful tool for surveillance after treatment. Guidelines for the management of MCC will likely continue to change as research on surveillance and treatment of MCC continues.