The C-terminus of the prototypical M2 muscarinic receptor localizes to the mitochondria and regulates cell respiration under stress conditions.

Muscarinic acetylcholine receptors are prototypical G protein-coupled receptors (GPCRs), members of a large family of 7 transmembrane receptors mediating a wide variety of extracellular signals. We show here, in cultured cells and in a murine model, that the carboxyl terminal fragment of the muscarinic M2 receptor, comprising the transmembrane regions 6 and 7 (M2tail), is expressed by virtue of an internal ribosome entry site localized in the third intracellular loop. Single-cell imaging and import in isolated yeast mitochondria reveals that M2tail, whose expression is up-regulated in cells undergoing integrated stress response, does not follow the normal route to the plasma membrane, but is almost exclusively sorted to the mitochondria inner membrane: here, it controls oxygen consumption, cell proliferation, and the formation of reactive oxygen species (ROS) by reducing oxidative phosphorylation. Crispr/Cas9 editing of the key methionine where cap-independent translation begins in human-induced pluripotent stem cells (hiPSCs), reveals the physiological role of this process in influencing cell proliferation and oxygen consumption at the endogenous level. The expression of the C-terminal domain of a GPCR, capable of regulating mitochondrial function, constitutes a hitherto unknown mechanism notably unrelated to its canonical signaling function as a GPCR at the plasma membrane. This work thus highlights a potential novel mechanism that cells may use for controlling their metabolism under variable environmental conditions, notably as a negative regulator of cell respiration.

Photodynamic Therapy for the Treatment of Bowen's Disease: A Review on Efficacy, Non-Invasive Treatment Monitoring, Tolerability, and Cosmetic Outcome.

Bowen's disease represents the in situ form of cutaneous squamous cell carcinoma; although it has an excellent prognosis, 3-5% of lesions progress to invasive cutaneous squamous cell carcinoma, with a higher risk in immunocompromised patients. Treatment is therefore always necessary, and conventional photodynamic therapy is a first-line option. The aim of this review is to provide an overview of the clinical response, recurrence rates, safety, and cosmetic outcome of photodynamic therapy in the treatment of Bowen's disease, considering different protocols in terms of photosensitizers, light source, and combination treatments. Photodynamic therapy is a valuable option for tumors at sites where wound healing is poor/delayed, in the case of multiple and/or large tumors, and where surgery would be difficult or invasive. Dermoscopy and reflectance confocal microscopy can be used as valuable tools for monitoring the therapeutic response. The treatment is generally well tolerated, with mild side effects, and is associated with a good/excellent cosmetic outcome. Periodic follow-up after photodynamic therapy is essential because of the risk of recurrence and progression to cSCC. As the incidence of keratinocyte tumors increases, the therapeutic space for photodynamic therapy will further increase.

Molecular Profile of Subungual Melanoma: A MelaNostrum Consortium Study of 68 Cases Reporting BRAF, NRAS, KIT, and TERT Promoter Status.

BACKGROUND: Subungual melanoma (SM) is an unusual type of melanocytic tumor affecting the nail apparatus. The mutational prevalence of the most prominently mutated genes in melanoma has been reported in small cohorts of SM, with unclear conclusions on whether SM is different from the rest of melanomas arising in acral locations or not. Hence, the molecular profile of a large series of SM is yet to be described. OBJECTIVES: The aim of this study was to describe the molecular characteristics of a large series of SM and their association with demographic and histopathological features. METHODS: Patients diagnosed with SM between 2001 and 2021 were identified from six Spanish and Italian healthcare centers. The mutational status for BRAF, NRAS, KIT, and the promoter region of TERT (TERTp) were determined either by Sanger sequencing or next-generation sequencing. Clinical data were retrieved from the hospital databases to elucidate potential associations. RESULTS: A total of 68 SM cases were included. Mutations were most common in BRAF (10.3%) and KIT (10%), followed by NRAS (7.6%), and TERTp (3.8%). Their prevalence was similar to that of non-subungual acral melanoma but higher in SM located on the hand than on the foot. CONCLUSIONS: To date, this study represents the largest cohort of SM patients with data on the known driver gene mutations. The low mutation rate supports a different etiopathogenic mechanism for SM in comparison of non-acral cutaneous melanoma, particularly for SM of the foot.

The dynamics of circulating tumour DNA (ctDNA) during treatment reflects tumour response in advanced melanoma patients.

Despite the introduction of targeted (BRAFi/MEKi) and immune checkpoint inhibitors (ICIs) has significantly reduced the recurrence rate and improved the overall survival (OS) of patients with Stage III and IV melanoma, only a percentage will benefit of durable disease control. The aim of this study was to examine whether the levels of circulating tumour DNA (ctDNA) in plasma of advanced melanoma patients undergoing BRAFi/MEKi or ICIs vary according to the patients' survival outcomes (i.e. progression-free survival (PFS) and OS) and disease progression. Plasma samples of Stage III-IV melanoma patients were collected at baseline (treatment initiation) and thereafter every 3 months. Circulating BRAFV600E/K and NRASQ61R/K mutations were analysed through droplet digital PCR (ddPCR, Bio-Rad) in a total of 177 plasma samples from 48 melanoma patients (19 Stage III, 29 Stage IV). Baseline ctDNA concentration was significantly associated with OS (HR = 1.003, 95% CI = 1.000-1.006, p = 0.043) and PFS (HR = 1.004, 95% CI = 1.000-1.007, p = 0.029) independent of clinical-prognostic confounders. For each unit increase in the ∆ctDNA (concentration difference between the last follow-up and baseline) there was a 24% increased risk of disease progression, irrespective of treatment type and stage at diagnosis (OR = 1.24, 95% CI = 1.03-1.49, p = 0.020, AUC = 0.93). Patients with reduction of ctDNA level from baseline to the last follow-up had longer OS (HR = 0.14; 95% CI = 0.05-0.44, p = 0.001) and PFS (HR = 0.08; 95% CI = 0.03-0.27, p < 0.0001) compared to patients with increased ctDNA, including adjustment for confounding factors. Our findings suggest that variation of ctDNA over time during melanoma treatment reflects the clinical outcome and tumour response to therapy and might be helpful in clinical monitoring.

Cytokine profile characterization of naïve patients with psoriasis and psoriatic arthritis: implications for a pathogenic disease continuum.

Background: The idea of psoriatic disease continuum has been progressively prompted based on the advances of the knowledge about the pathogenic steps underpinning the occurrence of psoriasis (PSO) and psoriatic arthritis (PSA). To evaluate biomolecules (inflammatory cytokines, inflammatory chemokines, cell adhesion and cellular mediators) in naïve patients with PSO, PSA with PSO, and PSA sine PSO. To stratify the results considering the presence of psoriatic nail involvement, extensive skin disease and obesity evaluating all involved patients. Methods: By multiplex technology, 20 serum biomolecules were assessed with the inclusion of pro-inflammatory cytokines (GM-CSF, IFN-γ, IL-1α, IL-1ß, IL-6, IL-8, IL-12p70, IL-17A, IL-23, TNF), anti-inflammatory cytokines (IFN-α, IL-4, IL-10, IL-13), inflammatory chemokines (IP-10, MCP-1, MIP-1α, MIP-1ß), cell adhesion and cellular mediators (ICAM-1, E-selectin, P-selectin). The assessment of possible statistical differences between the means of the three groups was performed by One-Way ANOVA. In addition, by non-parametric T-tests, we stratified the results according to selected clinical characteristics (psoriatic nail involvement, PASI ≥ 10, BMI ≥ 30). Results: In 80 assessed naïve patients, patients with PSO showed significant increases of E-selectin (p=0.021) and IL-8 (0.041) than other groups. In patients with PSA with PSO, significant higher levels of ICAM-1 were observed (p=0.009) than other groups. We did not observe further differences comparing pro-inflammatory and anti-inflammatory cytokines, inflammatory chemokines, and cell adhesion and cellular mediators in patients with PSO, PSA with PSO, and PSA sine PSO. Patients with psoriatic onychopathy showed significant increased levels of ICAM-1 (p=0.010) and IP-10 (0.030) than others. In patients with PASI ≥ 10, significantly enhanced values of IL-8 (p=0.004), TNF (p=0.013), E-selectin (p=0.004), MIP-1α (p=0.003), and MIP-1ß (p=0.039). In patients with BMI ≥ 30, significantly higher levels of E-selectin were pointed out (p=0.035) than others. Conclusion: Our findings may suggest that a similar cytokine profile may characterize naïve patients with PSO, PSA with PSO, and PSA sine PSO, reinforcing the concept of psoriatic disease continuum. However, some differences may be also shown, underlying possible pathogenic differences and leading to the clinical heterogeneity of these patients.

T Cell Immunoglobulin and Mucin Domain 3 (TIM-3) in Cutaneous Melanoma: A Narrative Review.

T cell immunoglobulin and mucin domain 3 (TIM-3) is an inhibitory immunocheckpoint that belongs to the TIM gene family. Monney et al. first discovered it about 20 years ago and linked it to some autoimmune diseases; subsequent studies have revealed that some tumours, including melanoma, have the capacity to produce inhibitory ligands that bind to these receptor checkpoints on tumour-specific immune cells. We conducted a literature search using PubMed, Web of Science (WoS), Scopus, Google Scholar, and Cochrane, searching for the following keywords: "T cell immunoglobulin and mucin-domain containing-3", "TIM-3" and/or "Immunocheckpoint inhibitors" in combination with "malignant melanoma" or "human malignant melanoma" or "cutaneous melanoma". The literature search initially turned up 117 documents, 23 of which were duplicates. After verifying eligibility and inclusion criteria, 17 publications were ultimately included. A growing body of scientific evidence considers TIM-3 a valid inhibitory immuno-checkpoint with a very interesting potential in the field of melanoma. However, other recent studies have discovered new roles for TIM-3 that seem almost to contradict previous findings in this regard. All this demonstrates how common and valid the concept of 'pleiotropism' is in the TME field, in that the same molecule can behave completely or partially differently depending on the cell type considered or on temporary conditions. Further studies, large case series, and a special focus on the immunophenotype of TIM-3 are absolutely necessary in order to explore this highly promising topic in the near future.

"Your Skin Tells You" Campaign for Keratinocyte Cancers: When Individuals' Selection Makes the Difference.

BACKGROUND: Prevention campaigns for skin cancers have focused primarily on melanoma, and over time there has been increasing awareness of the need to select the population to be screened to maximize program effectiveness. OBJECTIVES: The objective of the study was to report the results of a free dermatological initiative, as part of an awareness campaign dedicated to keratinocyte cancers, targeting individuals pre-selected through a short questionnaire. METHODS: One day of dermatological consultations was held at 15 dermato-oncology referral centers during May 22-June 30, 2021. For selection, individuals answered a telephone interview consisting of 7 yes/no questions on risk factors. Demographics, clinical characteristics of suspicious tumors, and histopathologic diagnosis of excised lesions were collected. Suspicion rate, detection rate, and positive predictive values (PPVs) for any skin cancer, basal cell carcinoma (BCC), cutaneous squamous cell carcinoma (cSCC), and melanoma were calculated. RESULTS: A total of 320 individuals (56.9% males; 43.1% females) with a median age of 69.6 (range 21-91) years qualified for the screening initiative. Overall, skin cancers and precancerous lesions were diagnosed in 65.9% of the patients. Suspicion rate was 28.7% for any skin cancer (92/320), 22.8% for BCC (73/320), 4.7% for cSCC (15/320), and 1.2% for melanoma (4/320). Detection rate was 23.4% for any skin cancer (PPV 93.7%), 18.1% for BCC (PPV 95.1%), 4.4% for cSCC (PPV 93.3%), and 0.9% for melanoma (PPV 75%). CONCLUSIONS: Selection of individuals at high risk is a cost-effective approach for early detection campaigns for keratinocyte cancers.

The Alternative TrkAIII Splice Variant, a Targetable Oncogenic Participant in Human Cutaneous Malignant Melanoma.

Post-therapeutic relapse, poor survival rates and increasing incidence justify the search for novel therapeutic targets and strategies in cutaneous malignant melanoma (CMM). Within this context, a potential oncogenic role for TrkA in CMM is suggested by reports of NTRK1 amplification, enhanced TrkA expression and intracellular TrkA activation associated with poor prognosis. TrkA, however, exhibits tumour-suppressing properties in melanoma cell lines and has recently been reported not to be associated with CMM progression. To better understand these contradictions, we present the first analysis of potential oncogenic alternative TrkA mRNA splicing, associated with TrkA immunoreactivity, in CMMs, and compare the behaviour of fully spliced TrkA and the alternative TrkAIII splice variant in BRAF(V600E)-mutated A375 melanoma cells. Alternative TrkA splicing in CMMs was associated with unfolded protein response (UPR) activation. Of the several alternative TrkA mRNA splice variants detected, TrkAIII was the only variant with an open reading frame and, therefore, oncogenic potential. TrkAIII expression was more frequent in metastatic CMMs, predominated over fully spliced TrkA mRNA expression in ≈50% and was invariably linked to intracellular phosphorylated TrkA immunoreactivity. Phosphorylated TrkA species resembling TrkAIII were also detected in metastatic CMM extracts. In A375 cells, reductive stress induced UPR activation and promoted TrkAIII expression and, in transient transfectants, promoted TrkAIII and Akt phosphorylation, enhancing resistance to reductive stress-induced death, which was prevented by lestaurtinib and entrectinib. In contrast, fully spliced TrkA was dysfunctional in A375 cells. The data identify fully spliced TrkA dysfunction as a novel mechanism for reducing melanoma suppression, support a causal relationship between reductive stress, UPR activation, alternative TrkAIII splicing and TrkAIII activation and characterise a targetable oncogenic pro-survival role for TrkAIII in CMM.

Secukinumab in Patients with Psoriasis and a Personal History of Malignancy: A Multicenter Real-Life Observational Study.

INTRODUCTION: There is limited evidence to guide clinicians on the treatment of psoriasis with biologics in patients with a history of malignancy who are often excluded from clinical trials investigating biologics. The aim of this work is to report a multicenter real-life experience of secukinumab treatment in patients with psoriasis and a personal history of cancer. METHODS: This retrospective observational study included adult patients with moderate-to-severe plaque psoriasis treated with secukinumab for at least 24 weeks and a previous diagnosis of cancer at 15 Italian referral centers. The primary endpoint of the study was tumor recurrence or progression and new cancer diagnosis during treatment. Secondary outcome assessment of secukinumab effectiveness (reduction of Psoriasis Area and Severity Index [PASI] score, improvement of Dermatology Life Quality Index [DLQI], itch and pain). RESULTS: Forty-two patients (27 male) were included. Malignancy was diagnosed in the previous 5 years in 21 (56.8%) and in the previous 10 years in 37 (88.1%). The mean interval between cancer diagnosis and the start of secukinumab treatment was 3.5 ± 3.3 years. No tumor recurrence nor progression occurred over a mean of 56 ± 31.7 weeks of treatment. Three patients developed a new malignancy not related to the previous cancer. At week 48, PASI 90 was reached by 64.7% of patients and PASI 100 by 38.2%. Mean DLQI, itch, and pain VAS scores significantly improved during treatment. CONCLUSIONS: Our multicenter real-life experience is the largest reported to date focusing on a specific biologic and adds evidence to the safety of secukinumab in psoriatic patients with a personal history of cancer.

Risk Factors and Diagnosis of Advanced Cutaneous Squamous Cell Carcinoma.

Cutaneous squamous cell carcinoma (cSCC) is the second most common cancer affecting humans. The combination of the increasing incidence and high mortality in advanced stages of the disease, defines cSCC as an emerging public health problem. Advanced disease includes metastatic and locally advanced cSCC. Metastatic disease refers to the presence of locoregional metastasis (in transit or to regional lymph nodes) or distant metastasis. Locally advanced disease has been defined as non-metastatic cSCC that is unlikely to be cured with surgery, radiotherapy, or combination treatment. While metastatic cSCC is easily diagnosed, locally advanced disease lacks consensus definition and diagnosis is made after multidisciplinary board consultation. Identifying patients with aggressive cSCC at highest risk for relapse may prevent the occurrence of advanced disease. Prognostic factors suggested by most guidelines include tumor diameter (>2 cm), localization on temple/ear/lip/area, thickness (>6 mm), or invasion beyond subcutaneous fat, poor grade of differentiation, desmoplasia, perineural invasion, bone erosion, immunosuppression, undefined borders, recurrence, growth rate, site of prior radiotherapy, and lymphatic or vascular involvement. Although risk factors associated with worse outcomes are well known, there is still a gap of knowledge on the precise risk of each factor taken individually. The aim of this review is to summarize cSCC prognostic factors and encompass the various staging systems to guide management and follow-up in cSCC patients at higher risk for local recurrence and metastasis. Finally, we describe the hallmarks of the advanced disease. Advanced cSCC diagnosis should be made by a multidisciplinary board considering patients' performance status and disease characteristics.

Carfilzomib Enhances the Suppressive Effect of Ruxolitinib in Myelofibrosis.

As the first FDA-approved tyrosine kinase inhibitor for treatment of patients with myelofibrosis (MF), ruxolitinib improves clinical symptoms but does not lead to eradication of the disease or significant reduction of the mutated allele burden. The resistance of MF clones against the suppressive action of ruxolitinib may be due to intrinsic or extrinsic mechanisms leading to activity of additional pro-survival genes or signalling pathways that function independently of JAK2/STAT5. To identify alternative therapeutic targets, we applied a pooled-shRNA library targeting ~5000 genes to a JAK2V617F-positive cell line under a variety of conditions, including absence or presence of ruxolitinib and in the presence of a bone marrow microenvironment-like culture medium. We identified several proteasomal gene family members as essential to HEL cell survival. The importance of these genes was validated in MF cells using the proteasomal inhibitor carfilzomib, which also enhanced lethality in combination with ruxolitinib. We also showed that proteasome gene expression is reduced by ruxolitinib in MF CD34+ cells and that additional targeting of proteasomal activity by carfilzomib enhances the inhibitory action of ruxolitinib in vitro. Hence, this study suggests a potential role for proteasome inhibitors in combination with ruxolitinib for management of MF patients.

Molecular alterations in basal cell carcinoma subtypes.

A number of genes have been implicated in the pathogenesis of BCC in addition to the Hedgehog pathway, which is known to drive the initiation of this tumour. We performed in-depth analysis of 13 BCC-related genes (CSMD1, CSMD2, DPH3 promoter, PTCH1, SMO, GLI1, NOTCH1, NOTCH2, TP53, ITIH2, DPP10, STEAP4, TERT promoter) in 57 BCC lesions (26 superficial and 31 nodular) from 55 patients and their corresponding blood samples. PTCH1 and TP53 mutations were found in 71.9% and 45.6% of BCCs, respectively. A high mutation rate was also detected in CSMD1 (63.2%), NOTCH1 (43.8%) and DPP10 (35.1%), and frequent non-coding mutations were identified in TERT (57.9%) and DPH3 promoter (49.1%). CSMD1 mutations significantly co-occurred with TP53 changes (p = 0.002). A significant association was observed between the superficial type of BCC and PTCH1 (p = 0.018) and NOTCH1 (p = 0.020) mutations. In addition, PTCH1 mutations were significantly associated with intermittent sun exposure (p = 0.046) and the occurrence of single lesions (p = 0.021), while NOTCH1 mutations were more frequent in BCCs located on the trunk compared to the head/neck and extremities (p = 0.001). In conclusion, we provide further insights into the molecular alterations underlying the tumorigenic mechanism of superficial and nodular BCCs with a view towards novel rationale-based therapeutic strategies.

Sequential treatment with calcitriol and methyl aminolevulinate-daylight photodynamic therapy for patients with multiple actinic keratoses of the upper extremities.

BACKGROUND: Topical photodynamic therapy (PDT) is a widely used and effective treatment for actinic keratoses (AKs). However, cure rates are significantly reduced for AKs on acral sites. We compared the sequential regimen of topical calcitriol and methyl aminolevulinate (MAL) daylight-PDT (CAL-DL-PDT) versus placebo and MAL-DL-PDT (P-DL-PDT) on acral AKs in an intra-individual, randomized trial. METHODS: Adult patients with multiple all grade AKs of the upper extremities were treated with daily topical calcitriol or placebo for 14 days followed by 2 sessions of DL-MAL-PDT. After 3 months, patients were evaluated for lesion response rate, both overall and by AK grade, and patient ≥ 75 % clearance rate. Safety assessments included pain VAS immediately after the first DL-PDT session, side effects after calcitriol pretreatment and 7 days after the first DL-PDT session. Cosmetic outcome by the physician and patient's preference were graded at the end of the study. RESULTS: Forty-two patients were enrolled and 36/42 completed the study. After 3 months, the overall lesion response rate and patient ≥ 75 % clearance rate of CAL-DL-PDT were higher, albeit not significantly, than P-DL-PDT. According to grade, response rate of grouped AK II/III was significantly higher for CAL-DL-PDT than for P-DL-PDT while similar results were observed for grade I AKs. Mild erythema and itch were reported after calcitriol application. No significant difference was observed in pain intensity. Local skin reactions occurred more frequently on the CAL-DL-PDT-treated sides. Cosmetic outcome did not differ but overall subject's preference was slightly significantly in favor of P-DL-PDT. CONCLUSIONS: CAL-DL-PDT is more effective than P-DL-PDT for thicker "difficult to treat" AKs on the upper extremities but is associated with increased local skin reactions.

Satisfaction and attitudes toward systemic treatments for psoriasis: A cross-sectional study.

In psoriasis patients, satisfaction and patients' attitude toward treatment are heterogeneous depending on several factors and remain poorly investigated, although the availability of several new targeted therapeutic options. A multicentre cross-sectional investigation was conducted to estimate treatment satisfaction and attitudes (awareness, trust, and therapeutic alliance) in a large population of adult psoriasis patients undergoing a systemic biologic or non-biologic agent for moderate-to-severe plaque-type psoriasis. Patients' satisfaction was measured using the Treatment Satisfaction Questionnaire for Medication II questionnaire and patients' attitudes toward treatment were evaluated using a Lickert scale. Results were related to patients' and treatment characteristics and therapeutic outcomes. The study included 899 psoriasis patients and demonstrated high-treatment satisfaction and positive attitudes toward systemic treatments, with greater influence of the perceived efficacy and the type of treatment. Biologic treatments and, in particular anti-IL17 agents showed higher results. More efforts in developing tools facilitating communication and exploring important aspects of patients' view are needed.

Updates on liquid biopsy: current trends and future perspectives for clinical application in solid tumors.

Despite advances in screening and therapeutics cancer continues to be one of the major causes of morbidity and mortality worldwide. The molecular profile of tumor is routinely assessed by surgical or bioptic samples, however, genotyping of tissue has inherent limitations: it represents a single snapshot in time and it is subjected to spatial selection bias owing to tumor heterogeneity. Liquid biopsy has emerged as a novel, non-invasive opportunity of detecting and monitoring cancer in several body fluids instead of tumor tissue. Circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), RNA (mRNA and microRNA), microvesicles, including exosomes and tumor "educated platelets" were recently identified as a source of genomic information in cancer patients which could reflect all subclones present in primary and metastatic lesions allowing sequential monitoring of disease evolution. In this review, we summarize the currently available information concerning liquid biopsy in breast cancer, colon cancer, lung cancer and melanoma. These promising issues still need to be standardized and harmonized across laboratories, before fully adopting liquid biopsy approaches into clinical practice.

Cutaneous and Mucosal Melanomas of Uncommon Sites: Where Do We Stand Now?

Melanomas arising at uncommon sites include a group of lesions related to unusual localizations in specific ethnic groups. The rarity of the disease often represents a limit to the participation of patients in specific trials. However, this peculiar genetic scenario has important therapeutic implications regarding new oncologic therapies. The aim of this article is to review the clinical features, somatic alterations and therapeutic options for melanomas of uncommon sites. They can be classified as cutaneous and mucosal lesions affecting the nail apparatus, palms/soles, oral mucosa, genital area and scalp. The prognosis may be worse compared to melanomas of other districts, and a prompt diagnosis may dramatically influence the outcome. Dermatologists and oncologists should therefore distinguish this melanoma subgroup in terms of surgical intervention and medical treatment. Due to the lack of mutations in genes usually found in cutaneous melanomas, the discovery of novel targets is required to develop new strategies and to change the prognosis of non-responders or wild-type patients.

Merkel cell carcinoma: an updated overview of clinico-pathological aspects, molecular genetics and therapy.

Merkel cell carcinoma (MCC) is a rare cutaneous neuroendocrine carcinoma of uncertain origin. MCC incidence varies by country and has been increasing among white populations over the last three decades. MCC occurs most commonly in elderly men and typically arises on sun-exposed areas. It is associated with a high mortality rate due to rapid growth and significant metastatic potential. Clinical and histopathological diagnosis are challenging, but prompt recognition of the disease is imperative for a correct management. Several hypotheses have been proposed to define the cell of origin, which still remains controversial. The discovery of Merkel cell polyoma virus, identified in the majority of MCCs, led to the hypothesis of the existence of two tumour subtypes showing biological, clinico-pathological and prognostic differences. Significant interest is nowadays directed to characterize MCC genomic alterations and microRNA (miRNA) expression profiles. Current treatment strategies for MCC depend on staging, and typically consist of surgery, radiation therapy, chemotherapy and/or, more recently, immunotherapy. The aim of this review is to provide an updated overview of MCC with a special focus on clinico-pathological aspects, molecular-genetics and therapy.