Polyomavirus-positive Merkel cell carcinoma: the beginning of the beginning.

Merkel cell carcinoma (MCC) is an aggressive, fast-growing, highly metastatic neuroendocrine skin cancer. The Merkel cell polyomavirus (MCPyV) is an oncogenic driver in the majority of MCC tumors. In this issue of the JCI, Hansen and authors report on their tracking of CD8+ T cells reactive to MCPyV T antigen (T-Ag) in the peripheral blood of 26 patients with MCC who were undergoing frontline anti-programmed cell death protein-1 (anti-PD-1) immunotherapy. They discovered unique T cell epitopes and used the power of bar-coded tetramers to portray immune checkpoint inhibitor-induced immunogenicity as a predictor of clinical response. These findings provide the foundation for therapeutic possibilities for MCC, including vaccines and adoptive T cell- and T cell receptor-driven (TCR-driven) treatments.

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.

Unusual Metastasis to Eyelid from Extraocular Merkel Cell Carcinoma.

Merkel cell carcinoma (MCC) is an unusual skin tumor that has a significant rate of distant and local metastases. It is known that primary MCC of the eyelid usually occurs at the upper eyelid. Here we report an unusual case of MCC metastasis to the eyelid. A 63-year-old male was diagnosed with MCC three years earlier after initially presenting with a mass in his right thigh. After histopathological diagnosis, the patient received medical therapy. During treatment, he developed multiple distant metastases and a firm, purple, vascularized lesion on the upper eyelid. We confirmed the lesion was an eyelid metastasis of MCC by histopathological examination and imaging methods. This case shows that extraocular MCC can metastasize to the eyelids, particularly the upper eyelid, where primary periocular MCC usually appears.

Systematic evaluation of Merkel cell carcinoma clinical practice guidelines using the AGREE II instrument.

Merkel cell carcinoma (MCC) is a rare type of skin cancer that requires a multidisciplinary approach with a variety of specialists for management and treatment. Clinical practice guidelines (CPGs) have recently been established to standardize management algorithms. The objective of this study was to appraise such CPGs via the Appraisal of Guidelines for Research and Evaluation (AGREE II) instrument. Eight CPGs were identified via systematic literature search following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria. Four appraisers trained in AGREE II protocols evaluated each CPG and deemed two CPGs as high quality, five as moderate quality, and one as low quality. Intraclass correlation coefficients (ICCs) were calculated to verify reviewer consistency as excellent, good, and moderate across four, one, and one domain, respectively. The majority of MCC CPGs are lacking in specifying stakeholder involvement, applicability, and rigor of development. The two high quality CPGs are from the Alberta Health Services (AHS) and the collaboration between the European Dermatology Forum, the European Association of Dermato-Oncology, and the European Organization of Research and Treatment of Cancer (EDF/EADO/EORTC). The EDF/EADO/EORTC CPG had the highest overall score with no significant deficiencies across any domain. An important limitation is that the AGREE II instrument is not designed to evaluate the validity of each CPG's recommendations; conclusions therefore can only be drawn about each CPG's developmental quality. Future MCC CPGs may benefit from garnering public perspectives, inviting external expert review, and considering available resources and implementation barriers during their developmental stages.

Analyses of tertiary lymphoid structures observed in cases of Merkel cell carcinoma showing spontaneous regression.

Merkel cell carcinoma (MCC) is a high-grade skin cancer, but spontaneous regression is observed at a markedly higher frequency than in other carcinomas. Although spontaneous regression is a phenomenon that greatly impacts treatment planning, we still cannot predict it. We previously reported on the prognostic impact of the presence or absence of tertiary lymphoid structures (TLS) and of Merkel cell polyomavirus (MCPyV) infection. To learn more about the spontaneous regression of MCC, detailed analyses were performed focusing on spontaneous regression cases. We collected 71 Japanese patients with MCC including 6 cases of spontaneous regression. Samples were analysed by immunostaining, spatial single-cell analysis using PhenoCycler, and RNA sequencing using the next-generation sequencer (NGS). All 6 cases of spontaneous regression were positive for MCPyV. TLS was positive in all 5 cases analysed. Spatial single-cell analyses revealed that PD-L1-positive tumour cells were in close proximity to CD20-positive B cell and CD3-, 4-positive T cells. Gene set enrichment analysis between MCPyV-positive and TLS-positive samples and other samples showed significantly high enrichment of "B-cell-mediated immunity" gene sets in the MCPyV-positive and TLS-positive groups. In conclusion, TLS may play an important role in the spontaneous regression of MCC.

Safety and effectiveness of avelumab in patients with Merkel cell carcinoma in general clinical practice in Japan: Post-marketing surveillance.

Avelumab, a programmed cell death ligand 1 blocking antibody, was approved for its first indication in Japan in September 2017 to treat unresectable Merkel cell carcinoma (MCC). Given that the pivotal JAVELIN Merkel 200 study only included a few Japanese patients, this post-marketing surveillance (PMS) evaluated the safety and effectiveness outcomes of patients with MCC who received avelumab in general clinical practice in Japan. This prospective, non-comparative, multicenter PMS included data from all patients with unresectable MCC who received avelumab between November 22, 2017 (avelumab launch date) and October 31, 2019. The primary objective was to evaluate avelumab safety (i.e., adverse events [AEs], adverse drug reactions [ADRs], and ADRs of safety specifications). The secondary objective was to evaluate avelumab effectiveness (i.e., objective response rate and overall survival [OS] rate). Seventy-five evaluable patients were included, of whom 81.3% experienced AEs of any grade (57.3% experienced AEs of grade ≥ 3; 41.3% experienced AEs of grade 5) and 61.3% experienced ADRs (14.7% experienced ADRs of grade ≥ 3; no grade 5 ADRs were observed). The most common ADRs were pyrexia (18.7%), infusion related reaction (10.7%), and chills (6.7%). The most common ADRs of safety specifications were infusion reactions (any grade: n = 21 [28.0%]; grade 3 or 4: n = 3 [4.0%]), thyroid dysfunction (n = 7 [9.3%]), and hepatic function disorders (n = 4 [5.3%]). The median observation period was 51 weeks. An objective response was achieved by 34/75 patients (45.3%; complete response, 24.0%; partial response, 21.3%) and 6- and 12-month OS rates were 77.7% and 59.6%, respectively. This PMS confirmed the clinical tolerability and effectiveness of avelumab in patients with MCC, with no new safety concerns. The risk-benefit profile of avelumab was comparable with that observed in clinical trials and remains favorable for use in general clinical practice in Japan.

Knockdown of nicotinamide N-methyltransferase suppresses proliferation, migration, and chemoresistance of Merkel cell carcinoma cells in vitro.

Merkel cell carcinoma (MCC) is an aggressive skin cancer, with a propensity for early metastasis. Therefore, early diagnosis and the identification of novel targets become fundamental. The enzyme nicotinamide N-methyltransferase (NNMT) catalyzes the reaction of N-methylation of nicotinamide and other analogous compounds. Although NNMT overexpression was reported in many malignancies, the significance of its dysregulation in cancer cell phenotype was partly clarified. Several works demonstrated that NNMT promotes cancer cell proliferation, migration, and chemoresistance. In this study, we investigated the possible involvement of this enzyme in MCC. Preliminary immunohistochemical analyses were performed to evaluate NNMT expression in MCC tissue specimens. To explore the enzyme function in tumor cell metabolism, MCC cell lines have been transfected with plasmids encoding for short hairpin RNAs (shRNAs) targeting NNMT mRNA. Preliminary immunohistochemical analyses showed elevated NNMT expression in MCC tissue specimens. The effect of enzyme downregulation on cell proliferation, migration, and chemosensitivity was then evaluated through MTT, trypan blue, and wound healing assays. Data obtained clearly demonstrated that NNMT knockdown is associated with a decrease of cell proliferation, viability, and migration, as well as with enhanced sensitivity to treatment with chemotherapeutic drugs. Taken together, these results suggest that NNMT could represent an interesting MCC biomarker and a promising target for targeted anti-cancer therapy.

The diagnostic utility of Merkel cell polyoma virus immunohistochemistry in cytology specimens.

OBJECTIVE: Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine neoplasm that predominantly affects elderly and immunocompromised patients. Merkel cell polyoma virus (MCPyV) is clonally integrated into the majority of MCCs and has been linked to patient outcomes, playing a central role in the pathogenesis of the disease. We aimed to assess the utility of MCPyV immunohistochemistry (IHC) in the diagnosis of MCC in cytology cell block specimens and correlating with clinicopathologic features. METHODS: Fifty-three cytology samples of MCC with sufficient cell block material were stained for MCPyV by IHC and scored semi-quantitatively in extent and intensity. Morphologic mimics of MCC including small cell lung carcinoma (n = 10), non-Hodgkin lymphoma (n = 10), basaloid squamous cell carcinoma (n = 6) and other neuroendocrine carcinomas (n = 8) were stained in parallel. Positive staining was defined as >1% of the tumour cells showing at least moderate staining intensity. RESULTS: The cytologic features of MCC were characterized by high nuclear-cytoplasmic ratios, hyperchromatic nuclei with 'salt and pepper' chromatin, and nuclear moulding. MCPyV was detected in 24 of 53 cases (45%). Staining was strong and diffuse in roughly half of the positive samples. Of the morphologic mimics, one follicular lymphoma showed strong and diffuse staining. In contrast to prior studies, we saw no association between MCPyV status and patient outcomes. CONCLUSION: Merkel cell polyoma virus IHC is highly specific (97%) for the diagnosis of MCC in our cohort, and can serve as a useful diagnostic tool for distinguishing MCC for morphologic mimics.

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.

Immunogenicity of avelumab in patients with metastatic Merkel cell carcinoma or advanced urothelial carcinoma.

Like other monoclonal antibodies, immune checkpoint inhibitors may be immunogenic in some patients, potentially affecting pharmacokinetics (PKs) and clinical outcomes. In post hoc analyses, we characterized antidrug antibody (ADA) development with avelumab monotherapy in patients with metastatic Merkel cell carcinoma (mMCC) from the JAVELIN Merkel 200 trial (first-line [1L; N = 116] and second-line or later [≥2L; N = 88] cohorts) or with advanced urothelial carcinoma (aUC) from the JAVELIN Bladder 100 (1L maintenance [N = 350]) and JAVELIN Solid Tumor (≥2L [N = 249]) trials. Treatment-emergent ADAs developed in a numerically higher proportion of patients with aUC (1L maintenance, 19.1%; ≥2L, 18.1%) versus mMCC (1L, 8.2%; ≥2L, 8.9%); incidences within tumor types were similar by line of therapy. In PK analyses, numerically lower avelumab trough concentration and higher baseline clearance were observed in treatment-emergent ADA+ versus ADA- subgroups; however, differences were not clinically relevant. Numerical differences in overall survival, progression-free survival, or objective response rate by ADA status were observed; however, no clinically meaningful trends were identified. Proportions of patients with treatment-emergent adverse events (TEAEs; any grade or grade 3/4), serious TEAEs, TEAEs leading to treatment discontinuation, or infusion-related reactions were similar, with overlapping 80% confidence intervals between ADA subgroups. Efficacy and safety observations were similar in subgroups defined by early development of ADA+ status during treatment. In conclusion, no meaningful differences in PKs, efficacy, and safety were observed between subgroups of avelumab-treated patients with different ADA status. Overall, these data suggest that ADAs are not relevant for treatment decisions with avelumab.

Avelumab in the Treatment of Advanced Merkel Cell Carcinoma: A Systematic Review.

BACKGROUND: Avelumab, a programmed death ligand-1 inhibitor, has shown success in providing durable responses for difficult-to-treat Merkel cell carcinomas (MCCs). OBJECTIVE: Evaluate the efficacy and safety of avelumab in the treatment of advanced MCC. METHODS: Studies reporting the use of avelumab as a monotherapy or in combination with other agents in the treatment of stage III or IV (advanced) MCC were included. The primary outcomes were overall response rate, overall survival (OS), and treatment-related adverse events. RESULTS: A total of 48 studies were included, involving 1,565 patients with advanced MCC. Most patients were male (1,051, 67.3%) with stage IV MCC (517, 97.0%). The overall response rate was 46.1% (partial response-25.4% and complete response-20.7%) after a mean follow-up period of 9.5 months. Kaplan-Meier survival curves for the pooled stage III and IV group demonstrated OS rates of 58% at 1 year, 47% at 2 years, and 28% at 5 years after completion of treatment with avelumab (median OS: 23.1 months). The most common treatment-related adverse events consisted of constitutional (44%), gastrointestinal (19%), and dermatologic (12%) symptoms. CONCLUSION: Avelumab monotherapy and combination therapy have shown success in the overall response rate and survival for patients with advanced MCC.

Tumor reactive γδ T cells contribute to a complete response to PD-1 blockade in a Merkel cell carcinoma patient.

Immunotherapies targeting PD-1/PD-L1 are now widely used in the clinic to treat a variety of malignancies. While most of the research on T cell exhaustion and PD-1 blockade has been focused on conventional αß T cells, the contribution of innate-like T cells such as γδ T cells to anti-PD-1/PD-L1 mediated therapy is limited. Here we show that tumor reactive γδ T cells respond to PD-1 blockade in a Merkel cell carcinoma (MCC) patient experiencing a complete response to therapy. We find clonally expanded γδ T cells in the blood and tumor after pembrolizumab treatment, and this Vγ2Vδ1 clonotype recognizes Merkel cancer cells in a TCR-dependent manner. Notably, the intra-tumoral γδ T cells in the MCC patient are characterized by higher expression of PD-1 and TIGIT, relative to conventional CD4 and CD8 T cells. Our results demonstrate that innate-like T cells could also contribute to an anti-tumor response after PD-1 blockade.

Neoadjuvant PD-1 Inhibitors: A Tale of Two Cases.

Treatment responses for locally advanced cutaneous squamous cell carcinoma (cSCC) and Merkel cell carcinoma (MCC) are often short lived and are marred with recurrences. The introduction of adjuvant PD-1 inhibitors has demonstrated significant improvement in both, response rates, and duration of response. For patients with high-risk resectable disease, adjuvant treatments have not demonstrated an ability to reduce recurrence risk. However, there is an opportunity in the neoadjuvant setting to alter recurrence risk. Here we dem-onstrate two cases of neoadjuvant treatment of cSCC and MCC with impressive results.  J Drugs Dermatol. 2024;23(2):     doi:10.36849/JDD.7043e.

Circulating cancer-specific CD8 T cell frequency is associated with response to PD-1 blockade in Merkel cell carcinoma.

Understanding cancer immunobiology has been hampered by difficulty identifying cancer-specific T cells. Merkel cell polyomavirus (MCPyV) causes most Merkel cell carcinomas (MCCs). All patients with virus-driven MCC express MCPyV oncoproteins, facilitating identification of virus (cancer)-specific T cells. We studied MCPyV-specific T cells from 27 patients with MCC using MCPyV peptide-HLA-I multimers, 26-color flow cytometry, single-cell transcriptomics, and T cell receptor (TCR) sequencing. In a prospective clinical trial, higher circulating MCPyV-specific CD8 T cell frequency before anti-PD-1 treatment was strongly associated with 2-year recurrence-free survival (75% if detectable, 0% if undetectable, p = 0.0018; ClinicalTrial.gov: NCT02488759). Intratumorally, such T cells were typically present, but their frequency did not significantly associate with response. Circulating MCPyV-specific CD8 T cells had increased stem/memory and decreased exhaustion signatures relative to their intratumoral counterparts. These results suggest that cancer-specific CD8 T cells in the blood may play a role in anti-PD-1 responses. Thus, strategies that augment their number or mobilize them into tumors could improve outcomes.

High-volume facilities are significantly more likely to use guideline-adherent systemic immunotherapy for metastatic Merkel cell carcinoma: implications for cancer care regionalization.

Merkel cell carcinoma (MCC) is a neuroendocrine skin cancer with a high rate of mortality. While still relatively rare, the incidence of MCC has been rapidly rising in the US and around the world. Since 2017, two immunotherapeutic drugs, avelumab and pembrolizumab, have been FDA-approved for the treatment of metastatic MCC and have revolutionized outcomes for MCC. However, real-world outcomes can differ from clinical trial data, and the adoption of novel therapeutics can be gradual. We aimed to characterize the treatment practices and outcomes of patients with metastatic MCC across the US. A retrospective cohort study of adult cases of MCC in the National Cancer Database diagnosed from 2004 to 2019 was performed. Multivariable logistic regressions to determine the association of a variety of patient, tumor, and system factors with likelihood of receipt of systemic therapies were performed. Univariate Kaplan-Meier and multivariable Cox survival regressions were performed. We identified 1017 cases of metastatic MCC. From 2017 to 2019, 54.2% of patients received immunotherapy. This increased from 45.1% in 2017 to 63.0% in 2019. High-volume centers were significantly more likely to use immunotherapy (odds ratio 3.235, p = 0.002). On univariate analysis, patients receiving systemic immunotherapy had significantly improved overall survival (p < 0.001). One-, 3-, and 5-year survival was 47.2% (standard error [SE] 1.8%), 21.8% (SE 1.5%), and 16.5% (SE 1.4%), respectively, for patients who did not receive immunotherapy versus 62.7% (SE 3.5%), 34.4% (SE 3.9%), and 23.6% (SE 4.4%), respectively, for those who did (Fig. 1). In our multivariable survival regression, receipt of immunotherapy was associated with an approximately 35% reduction in hazard of death (hazard ratio 0.665, p < 0.001; 95% CI 0.548-0.808). Our results demonstrate that the real-world survival advantage of immunotherapy for metastatic MCC is similar to clinical trial data. However, many patients with metastatic disease did not receive this guideline-recommended therapy in our most recent study year, and use of immunotherapy is higher at high-volume centers. This suggests that regionalization of care to high-volume centers or dissemination of their practices, may ultimately improve patient survival.

NCCN Guidelines® Insights: Merkel Cell Carcinoma, Version 1.2024.

The NCCN Guidelines for Merkel Cell Carcinoma (MCC) provide recommendations for diagnostic workup, clinical stage, and treatment options for patients. The panel meets annually to discuss updates to the guidelines based on comments from expert review from panel members, institutional review, as well as submissions from within NCCN and external organizations. These NCCN Guidelines Insights focus on the introduction of a new page for locally advanced disease in the setting of clinical node negative status, entitled "Clinical N0 Disease, Locally Advanced MCC." This new algorithm page addresses locally advanced disease, and the panel clarifies the meaning behind the term "nonsurgical" by further defining locally advanced disease. In addition, the guideline includes the management of in-transit disease and updates to the systemic therapy options.