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

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

The role of micrometastasis in high-risk skin cancers

The propensity to metastasize is the most important prognostic indicator for solid cancers. New insights into the mechanisms of early carcinogenesis have revealed micrometastases are generated far earlier than previously thought. Evidence supports a synergistic relationship between vascular and lymphatic seeding which can occur before there is clinical evidence of a primary tumour. Early vascular seeding prepares distal sites for colonisation while regional lymphatics are co-opted to promote facilitative cancer cell mutations. In response, the host mounts a global inflammatory and immunomodulatory response towards these cells supporting the concept that cancer is a systemic disease. Cancer staging systems should be refined to better reflect cancer cell loads in various tissue compartments while clinical perspectives should be broadened to encompass this view when approaching high-risk cancers. Measured adjunctive therapies implemented earlier for low-volume, in-transit cancer offers the prospect of preventing advanced disease and the need for heroic therapeutic interventions. This review seeks to re-appraise how we view the metastatic process for solid cancers. It will explore in-transit metastasis in the context of high-risk skin cancer and how it dictates disease progression. It will also discuss how these implications will influence our current staging systems and its consequences on management.

Moderne Diagnostik und Therapie des Merkelzellkarzinoms

Das Merkelzellkarzinom (MCC) ist ein seltener, aggressiver Hauttumor mit epithelialer und neuroendokriner Differenzierung, dessen Inzidenz in den letzten Jahrzehnten deutlich zugenommen hat. Risikofaktoren sind fortgeschrittenes Lebensalter, heller Hauttyp, UV‐Exposition und Immunsuppression. Pathogenetisch wird ein durch das Merkelzell‐Polyomavirus (MCPyV) hervorgerufener Typ von einem UV‐induzierten Typ mit hoher Tumormutationslast unterschieden.

Klinisch präsentiert sich das MCC als meist schmerzloser, schnell wachsender, rötlich‐violetter Tumor mit glänzender Oberfläche, der bevorzugt im Kopf‐Hals‐Bereich und an den distalen Extremitäten lokalisiert ist. Eine sichere Diagnose kann nur anhand histologischer und immunhistochemischer Merkmale gestellt werden. Bei Erstdiagnose weisen 20%–26% der Patienten lokoregionäre Metastasen und 8%–14% Fernmetastasen auf, weshalb eine Ausbreitungsdiagnostik unabdingbar ist. Bei fehlenden klinischen Hinweisen auf Metastasen wird eine Sentinel‐Lymphknotenbiopsie empfohlen.

Wesentliche Säulen der Therapie sind die Operation, die adjuvante oder palliative Strahlentherapie und in fortgeschrittenen inoperablen Stadien die medikamentöse Tumortherapie. Die Einführung von Immuncheckpoint‐Inhibitoren führte zu einem Paradigmenwechsel, da sich hiermit ein wesentlich langfristigeres Ansprechen und bessere Überlebensraten als mit Chemotherapie erreichen lassen. Zur Therapie des metastasierten MCC ist in Deutschland der PD‐L1‐Inhibitor Avelumab zugelassen, aber auch die PD‐1‐Antikörper Pembrolizumab und Nivolumab werden mit Erfolg eingesetzt. Adjuvante und neoadjuvante Therapiekonzepte, Immunkombinationstherapien und zielgerichtete Therapien als Monotherapie oder in Kombination mit Immuncheckpoint‐Inhibitoren befinden sich in klinischer Prüfung.

Modern diagnostics and treatment of Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare, aggressive skin cancer with epithelial and neuroendocrine differentiation, the incidence of which has increased substantially during the last decades. Risk factors include advanced age, fair skin type, UV exposure, and immunosuppression. Pathogenetically, a type caused by the Merkel cell polyomavirus is distinguished from a UV-induced type with a high tumor mutational burden. Clinically, MCC presents as a mostly painless, rapidly growing, reddish-violet tumor with a shiny surface, which is preferentially localized in the head-neck region and at the distal extremities. A reliable diagnosis can only be made based on histological and immunohistochemical features. At initial diagnosis, 20-26% of patients show locoregional metastases and 8-14% distant metastases, making staging examinations indispensable. If there is no clinical evidence of metastases, a sentinel lymph node biopsy is recommended. Essential columns of therapy are surgery, adjuvant or palliative radiotherapy and, in advanced inoperable stages, medicamentous tumor therapy. The introduction of immune checkpoint inhibitors has led to a paradigm shift, as they provide a considerably longer duration of response and better survival rates than chemotherapy. The PD-L1 inhibitor avelumab is approved for treatment of metastatic MCC in Germany, but the PD-1 antibodies pembrolizumab and nivolumab are also used with success. Adjuvant and neoadjuvant treatment concepts, immune combination therapies and targeted therapies as monotherapy or in combination with immune checkpoint inhibitors are in the clinical trial phase.

Radiation, Lymph Node Dissection, or Both: Management of Lymph Node Micrometastases from Merkel Cell Carcinoma

BACKGROUND

Regional lymph node micrometastases from Merkel cell carcinoma (MCC) can be treated with completion lymph node dissection (CLND) and/or radiation therapy (RT). It is unclear how these options compare in terms of survival benefits for patients.

PATIENTS AND METHODS

This retrospective cohort study used data from years 2012-2019 of the National Cancer Database. Patients with MCC and clinically negative, but pathologically positive, lymph node metastases who received RT to and/or CLND of the regional lymph node basin were included. Inverse probability weight balancing was performed using covariates followed by Cox proportional hazards modeling for survival analysis.

RESULTS

A total of 962 patients were included [median (interquartile range) age, 74 (67-80) years, 662 (68.8%) male patients, 926 (96.3%) white patients]. The majority (63%, n = 606) had a CLND only, while 18% (n = 173) had RT only, and 19% (n = 183) had both CLND and RT. From 2016 to 2019, usage of RT only increased from 10% to 31.8%. Multivariate analysis demonstrated that treatment modality was not associated with survival [RT versus CLND, hazard ratio (HR) 0.842, 95% confidence interval (CI) 0.621-1.142, p = 0.269, RT+CLND versus CLND, HR 1.029, 95% CI 0.775-1.367, p = 0.844]. This persisted after balancing weights (RT versus CLND, HR 0.837, 95% CI 0.614-1.142, p = 0.262, RT+CLND versus CLND, HR 1.085, 95% CI 0.801-1.470, p = 0.599).

CONCLUSIONS

The usage of RT for nodal micrometastasis in MCC is increasing as compared with CLND. This strategy appears to be safe, with no significant difference in survival outcomes.

The role of radiotherapy in the updated German S2k guideline for management of Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a radiosensitive tumor and the role of radiotherapy in the management of this disease was newly defined in the recently published update of the S2k guideline on Merkel cell carcinoma of the Association of Scientific Medical Societies in Germany (AWMF). While adjuvant radiotherapy of the tumor bed is broadly recommended, irradiation of the regional nodal region can be performed in patients with negative sentinel lymph nodes and high-risk factors. In patients with positive sentinel lymph nodes, it is an alternative to completion lymphadenectomy. The standard dose for adjuvant radiotherapy remains 50 Gy.

An update on Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare cancer of the skin characterized by a neuroendocrine phenotype and an aggressive clinical behavior. It frequently originates in sun-exposed body areas, and its incidence has steadily increased in the last three decades. Merkel cell polyomavirus (MCPyV) and ultraviolet (UV) radiation exposure are the main causative agents of MCC, and distinct molecular features have been documented in virus-positive and virus-negative malignancies. Surgery remains the cornerstone of treatment for localized tumors, but even when integrated with adjuvant radiotherapy is able to definitively cure only a fraction of MCC patients. While characterized by a high objective response rate, chemotherapy is associated with a short-lasting benefit of approximately 3 months. On the other hand, immune checkpoint inhibitors including avelumab and pembrolizumab have demonstrated durable antitumor activity in patients with stage IV MCC, and investigations on their use in the neoadjuvant or adjuvant setting are currently underway. Addressing the needs of those patients who do not persistently benefit from immunotherapy is currently one of the most compelling unmet needs in the field, and multiple clinical trials of new tyrosine kinase inhibitors (TKIs), peptide receptor radionuclide therapy (PRRT), therapeutic vaccines, immunocytokines as well as innovative forms of adoptive cellular immunotherapies are under clinical scrutiny at present.

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

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

An Internally Validated Prognostic Risk-Score Model for Disease-Specific Survival in Clinical Stage I and II Merkel Cell Carcinoma

BACKGROUND

Merkel cell carcinoma (MCC) is a rare cutaneous malignancy for which factors predictive of disease-specific survival (DSS) are poorly defined.

METHODS

Patients from six centers (2005-2020) with clinical stage I-II MCC who underwent sentinel lymph node (SLN) biopsy were included. Factors associated with DSS were identified using competing-risks regression analysis. Risk-score modeling was established using competing-risks regression on a training dataset and internally validated by point assignment to variables.

RESULTS

Of 604 patients, 474 (78.5%) and 128 (21.2%) patients had clinical stage I and II disease, respectively, and 189 (31.3%) had SLN metastases. The 5-year DSS rate was 81.8% with a median follow-up of 31 months. Prognostic factors associated with worse DSS included increasing age (hazard ratio [HR] 1.03, p = 0.046), male sex (HR 3.21, p = 0.021), immune compromise (HR 2.46, p = 0.013), presence of microsatellites (HR 2.65, p = 0.041), and regional nodal involvement (1 node: HR 2.48, p = 0.039; ≥2 nodes: HR 2.95, p = 0.026). An internally validated, risk-score model incorporating all of these factors was developed with good performance (AUC 0.738). Patients with ≤ 4.00 and > 4.00 points had 5-year DSS rates of 89.4% and 67.2%, respectively. Five-year DSS for pathologic stage I/II patients with > 4.00 points (n = 49) was 79.8% and for pathologic stage III patients with ≤ 4.00 points (n = 62) was 90.3%.

CONCLUSIONS

A risk-score model, including patient and tumor factors, based on DSS improves prognostic assessment of patients with clinically localized MCC. This may inform surveillance strategies and patient selection for adjuvant therapy trials.

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

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

Lymph node ratio predicts efficacy of postoperative radiation therapy in nonmetastatic Merkel cell carcinoma: A population-based analysis

BACKGROUND

After radical resection of a nonmetastatic Merkel cell carcinoma (M0 MCC), postoperative radiation therapy (RT) is recommended as it improves survival. However, the role of RT in specific subgroups of M0 MCC is unclear. We sought to identify whether there is a differential survival benefit from RT in specific M0 MCC patient subgroups.

METHODS

M0 MCC patients from the Surveillance, Epidemiology, and End Results (SEER) database registry were collected. The best prognostic age, tumor size, and lymph node ratio (LNR, ratio between positive lymph nodes and resected lymph nodes) cutoffs were calculated. The primary endpoint was overall survival (OS).

RESULTS

A total of 5644 M0 MCC patients (median age 77 years, 62% male) were included: 4022 (71%) node-negative (N0) and 1551 (28%) node-positive (N+). Overall, 2682 patients (48%) received RT. Age > 76.5 years, tumor size >13.5 mm, and LNR >0.215 were associated with worse OS. RT was associated with longer OS in the M0 MCC, N0, and N+ group and independently associated with a 25%, 27%, and 26% reduction in the risk for death, respectively. RT benefit on survival was increased in tumor size >13.5 mm in the N0 group and LNR >0.215 in the N+ group. No OS benefit from RT was observed in T4 tumors (N0 and N+ groups).

CONCLUSIONS

RT was associated with improved survival in M0 MCC, irrespective of the nodal status. LNR >0.215 is a useful prognostic factor for clinical decision-making and for stratification and interpretation of clinical trials.

Radiation therapy of cutaneous cancers

We present the update of the recommendations of the French society of oncological radiotherapy on radiotherapy of cutaneous cancers. The indications of radiotherapy for skin cancers are not clearly defined because of the lack of randomized trials or prospective studies. For basal cell carcinomas, radiotherapy frequently offers a good local control, but a randomized trial showed that surgery is more efficient and less toxic. Indications of radiotherapy are contra-indications of surgery for patients older than 60, non-sclerodermiform histology and located in non-sensitive areas. Adjuvant radiotherapy could be proposed to squamous cell carcinomas, in case of poor prognostic factors. Dose of 60 to 70Gy are usually required, and must be modulated to the size of the lesions. Adjuvant radiotherapy seems beneficial for desmoplastic melanomas but not for the other histological types. Prophylactic nodal irradiation (45 to 50Gy), for locally advanced tumors (massive nodal involvement), decreases the locoregional failure rate but do not increase survival. Adjuvant radio- therapy (50 to 56Gy) for Merkel cell carcinomas increases also the local control rate, as demonstrated by meta-analysis and a large epidemiological study. Nodal areas must be included, if there is no surgical exploration (sentinel lymph node dissection). Kaposi sarcomas are radiosensitive and could be treated with relatively low doses (24 to 30Gy). Also, cutaneous lymphomas are good indications for radiotherapy: B lymphomas are electively treated with limited fields. The role of total skin electron therapy for T-lymphomas is still discussed; but palliative radiotherapy is very efficient in case of cutaneous nodules.

Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare neuroendocrine carcinoma. The cellular origin of MCC may include Merkel cell precursors. The incidence of MCC has increased significantly however trends may have been confounded by evolving diagnostic criteria. The two key aetiologies of MCC are ultraviolet radiation and Merkel cell polyoma virus (MCPyV). Both have unique mechanisms of carcinogenesis. MCC presents non-specifically as a rapidly growing, red-to-violet nodule on sun-exposed areas. Diagnostic accuracy has improved through immunohistochemical markers such as CK-20. Lymph nodes should be evaluated in MCC through examination and sentinel biopsy. USS, CT, MRI and CT-PET may be useful in staging. Management depends on tumour location, stage and comorbidities. MCPyV status may guide treatment strategy in the future. Treatment for the primary MCC is commonly wide local excision followed by radiotherapy, guided by anatomical constraints. There is uncertainty about surgical margins. Treatments for nodal disease have not been determined through trials. They include nodal dissection or radiotherapy for clinically or radiologically apparent disease, and adjuvant nodal irradiation for negative nodes, microscopic disease or following nodal dissection for definite disease. Patients with loco-regional advanced inoperable disease should be considered for combination therapy including chemotherapy, radiotherapy, surgery and immunotherapy. Systemic therapy for advanced disease includes immune checkpoint inhibitors targeting the PD-1/PD-L1 pathway. Avelumab can improve survival in metastatic MCC. Immunotherapy may result in longer disease control. Various other immunotherapeutic and molecular agents are undergoing trials. MCC continues to have a high mortality characterized by high recurrence and early metastases.

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.

Multimodal Strategy in Localized Merkel Cell Carcinoma: Where Are We and Where Are We Heading?

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumor of the skin whose incidence is rising. Multimodal treatment is crucial in the non-metastatic, potentially curable setting. However, the optimal management of patients with non-metastatic MCC is still unclear. In addition, novel insights into tumor biology and newly developed treatments (e.g., immune checkpoint inhibitors) that dramatically improved outcomes in the advanced setting are being investigated in earlier stages with promising results. Nevertheless, the combination of new strategies with consolidated ones needs to be clarified. We reviewed available evidence supporting the current treatment recommendations of localized MCC with a focus on potentially ground-breaking future strategies. Advantages and disadvantages of the different treatment modalities, including surgery, radiotherapy, chemotherapy, and immunotherapy in the non-metastatic setting, are analyzed, as well as those of different treatment modalities (adjuvant as opposed to neoadjuvant). Lastly, we provide an outlook of remarkable ongoing studies and of promising agents and strategies in the treatment of patients with non-metastatic MCC.

Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare and extremely aggressive neuroendocrine carcinoma of the skin, with increasing incidence worldwide. This review intends to propose a comprehensive evaluation of MCC epidemiology, clinical features, pathogenetic mechanisms, diagnosis, and therapies. A section is dedicated to immunological aspects and another to the involvement of angiogenesis and angiogenic growth factors in MCC progression, proposing novel diagnostic and therapeutic approaches. Advanced MCC tumors have been treated with immune checkpoint inhibitors with effective results. Therefore, the state of art of this immunotherapy is also examined, reporting on the most recent clinical trials in the field. We conclude by underlining the achievements in the understanding of MCC pathology and indicating the present needs for effective diagnosis and therapeutic management of the disease.

Sentinel Node Biopsy for Nonmelanoma Skin Cancer of the Head and Neck

Sentinel lymph node biopsy has the potential to impact regional control and survival for high-risk cutaneous malignancy. The outcome of sentinel lymph node biopsy is a potential guide for treatment and surveillance. The population of high-risk nonmelanoma patients that will benefit from sentinel lymph node biopsy remains to be determined. Any cutaneous malignancy with a greater than 10% risk of occult metastasis should be considered for sentinel lymph node biopsy or active surveillance. Localized cutaneous squamous cell carcinoma lesions with multiple high-risk features and nearly all patients with localized Merkel cell carcinoma should be considered for sentinel lymph node biopsy.

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.

Regional lymph node irradiation in locally advanced Merkel cell carcinoma reduces regional and distant relapse and improves disease-specific survival

BACKGROUND

One-third of patients with Merkel cell carcinoma (MCC) present with locally advanced disease involving the regional lymph nodes, but indications for regional lymph node radiation therapy (rLN-RT) are not well established.

MATERIALS AND METHODS

72 patients with locally advanced MCC were retrospectively reviewed. Regional lymph nodes were addressed with observation, lymph node dissection (LND) alone, definitive nodal radiotherapy (DnRT), or LND plus adjuvant nodal radiotherapy (AnRT). Cox regression was used to compare treatment modalities in terms of regional recurrence-free survival (RRFS), distant recurrence-free survival (DRFS), disease-free survival (DFS) and disease-specific survival (DSS).

RESULTS

rLN-RT, including both DnRT and AnRT, improved RRFS (Hazard ratio (HR): 0.07, 95% confidence interval (CI): 0.01-0.40, p = 0.003), DRFS (HR: 0.28, CI: 0.11-0.76, p = 0.01), DFS (HR: 0.23, CI: 0.09-0.58, p = 0.002), and DSS (HR: 0.23, CI: 0.06-0.90, p = 0.03). AnRT improved DFS and DSS in high-risk subgroups (e.g., extranodal extension (ENE), ≥ 2 positive lymph nodes, or bulkier lymph nodes). The benefit of AnRT increased with higher disease burden. After controlling for these adverse factors, AnRT significantly improved RRFS (HR: 0.04, CI: 0.01-0.37, p = 0.004), DRFS (HR: 0.14, CI: 0.04-0.50, p = 0.003), DFS (HR: 0.09, CI: 0.02-0.33, p < 0.001), and DSS (HR: 0.21, CI: 0.05-0.89, p = 0.03).

CONCLUSION

rLN-RT, including both DnRT and AnRT, reduces relapse and death from MCC in patients with node-positive disease. AnRT is particularly beneficial for patients with ENE, multiple involved lymph nodes, or larger nodal foci of disease. These results argue for more liberal use of nodal RT for MCC patients who present with node-positive disease.

Current concepts and approaches to merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive and rare cutaneous cancer of the mechanoreceptor unit of the skin with a neuroendocrine origin. MCC incidence has been on the rise over the past two decades. Risk factors include old age, chronic UV exposure, and immunosuppression. Although MCC is a cutaneous malignancy that is often misdiagnosed as a benign nodule at the time of diagnosis, it has an aggressive disease course due to its high recurrence and metastatic potential. The PD-1/PD-L1 checkpoint blockade has recently shown promising results in the management of advanced MCC. Avelumab and pembrolizumab are considered the new standard of care for metastatic MCC. Despite advances in the field, studies are needed to elucidate the role of immunotherapy for patients who are resistant to treatment. Most ongoing clinical trials aim to assess the efficacy of checkpoint inhibitor combination therapies. This article reviews the most current literature on the surgical and medical management of MCC.

Merkel Cell Carcinoma - Current Controversies and Future Directions

Merkel cell carcinoma is a rare, aggressive neuroendocrine skin malignancy. Evidence for management comes from case series and single-arm trials. Optimal outcomes require assessment of the patient in a multidisciplinary team setting. Rapid diagnosis and staging are essential for locoregional control and may reduce metastasis. Sentinel lymph node biopsy (SLNB) adds prognostic information. FDG-positron emission tomography has high sensitivity and specificity and affects management in a quarter of cases. Surgical excision and radiotherapy provide good locoregional control even with positive margins. Wide surgical margins are needed if adjuvant radiotherapy is not used. It is uncertain whether adjuvant radiotherapy or elective surgery for uninvolved nodes or for patients selected by positive SLNB improves survival. Total doses of 50 Gy provide high levels of control for microscopic disease but at least 60 Gy should be given for macroscopic disease. Chemotherapy can be given safely with radiotherapy, but the benefit of adjuvant chemotherapy remains uncertain. Trials of adjuvant immune therapy are underway. Unresectable primaries might be controlled with radiotherapy alone or combination systemic therapy, radiotherapy and surgery. Metastatic disease often responds to chemotherapy, but the response duration can be short. Immunity is central to disease control. Immune checkpoint inhibitor treatment resulted in high response rates in chemotherapy-naive patients and lower rates in chemotherapy-refractory patients. Durable responses are observed.

Merkel Cell Carcinoma: A 28-Year Experience

OBJECTIVE

To evaluate the management and recurrence outcomes of head and neck Merkel cell carcinoma (HN-MCC) at a single institution.

STUDY DESIGN

A retrospective review of outcomes in patients with HN-MCC.

SETTING

A tertiary center from May 1990 to December 2018.

SUBJECTS AND METHODS

Electronic medical records of patients with HN-MCC were reviewed.

RESULTS

Sixty cases were included, with 67% (40 of 60) males and a mean age of 73.3 years. Imaging had a moderate sensitivity and specificity for detection of occult disease when compared with histopathologic analysis. Forty-two percent (25 of 60) of patients underwent neck dissection, and 12% (7 of 60) had a sentinel lymph node biopsy (SLNB). There was a high rate of negative SLNB findings. The majority of patients were treated with surgery alone (29 of 60), followed by a cohort (21 of 60) treated with surgery plus adjuvant treatment, and 10 of 60 patients were treated with radiation therapy with or without chemotherapy. Recurrence-free survival was 50%, 45%, and 42% at 1, 2, and 5 years.

CONCLUSIONS

We report higher recurrence rates and higher negative SLNB result rates than other studies. Our results affirm that imaging may not be a substitute for SLNB and that it had an intermediate ability to identify the occult disease. Traditional predictors, including SLNB and cervical node pathology, may not identify patients at risk for recurrence in HN-MCC. We report similar recurrence rates in patients who had treatment of the cervical nodes by radiation therapy or neck dissection as compared with those who did not receive neck treatment.

Management Recommendations for Merkel Cell Carcinoma-A Danish Perspective

Merkel cell carcinoma (MCC) is a rare malignant neuroendocrine carcinoma of the skin with a poor prognosis and an apparent increase in incidence. Due to its rarity, evidence-based guidelines are limited, and there is a lack of awareness among clinicians. This review constitutes the consensus management recommendations developed by the Danish MCC expert group and is based on a systematic literature search. Patients with localized disease are recommended surgical excision and adjuvant radiotherapy to the primary site; however, this may be omitted in patients with MCC with low risk features. Patients with regional lymph node involvement are recommended complete lymph node removal and adjuvant radiotherapy in case of extracapsular disease. Metastatic disease was traditionally treated with chemotherapy, however, recent clinical trials with immune therapy have been promising. Immune checkpoint inhibitors targeting the programmed cell death protein 1(PD-1)/programmed death-ligand 1(PD-L1) axis should therefore be strongly considered as first-line treatment for fit patients. A 5-year follow-up period is recommended involving clinical exam every 3 months for 2 years and every 6 months for the following 3 years and PET-CT one to two times a year or if clinically indicated. These national recommendations are intended to offer uniform patient treatment and hopefully improve prognosis.

Completion lymph node dissection for merkel cell carcinoma

BACKGROUND

Sentinel lymph node biopsy (SLNB) is widely used for Merkel cell carcinoma (MCC), however in SLNB positive MCC the role of completion lymph node dissection (CLND) with or without adjuvant radiation therapy is unclear.

OBJECTIVE

Our goal was to determine the impact of CLND and adjuvant radiation therapy on survival in SLNB positive MCC.

MATERIALS AND METHODS

We examined 447 patients with MCC with a positive SLNB in the National Cancer Data Base from 2012 to 2015. We compared patients who underwent CLND versus observation with or without adjuvant radiation.

RESULTS

Compared with CLND and adjuvant radiation (reference) treatment with observation (HR 3.54, CI 1.36-9.18) or CLND alone (HR 2.54, CI 1.03-6.27) were associated with worse overall survival after adjusting for clinicopathologic differences. In contrast treatment with adjuvant radiation alone without CLND was not associated with worse overall survival (HR 1.70, CI 0.74-3.92) compared with CLND and adjuvant radiation (reference).

CONCLUSIONS

In SLNB positive MCC, CLND alone is associated with worse survival compared with treatment with adjuvant radiation or both CLND and adjuvant radiation.