Feline papillomavirus-associated Merkel cell carcinoma: a comparative review with human Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare skin tumor that shares a similar immunophenotype with Merkel cells, although its origin is debatable. More than 80% of human MCC cases are associated with Merkel cell polyomavirus infections and viral gene integration. Recent studies have shown that the clinical and pathological characteristics of feline MCC are comparable to those of human MCC, including its occurrence in aged individuals, aggressive behavior, histopathological findings, and the expression of Merkel cell markers. More than 90% of feline MCC are positive for the Felis catus papillomavirus type 2 (FcaPV2) gene. Molecular changes involved in papillomavirus-associated tumorigenesis, such as increased p16 and decreased retinoblastoma (Rb) and p53 protein levels, were observed in FcaPV2-positive MCC, but not in FcaPV2-negative MCC cases. These features were also confirmed in FcaPV2-positive and -negative MCC cell lines. The expression of papillomavirus E6 and E7 genes, responsible for p53 degradation and Rb inhibition, respectively, was detected in tumor cells by in situ hybridization. Whole genome sequencing revealed the integration of FcaPV2 DNA into the host feline genome. MCC cases often develop concurrent skin lesions, such as viral plaque and squamous cell carcinoma, which are also associated with papillomavirus infection. These findings suggest that FcaPV2 infection and integration of viral genes are involved in the development of MCC in cats. This review provides an overview of the comparative pathology of feline and human MCC caused by different viruses and discusses their cell of origin.

Preliminary evidence that Merkel cells exert chemosensory functions in human epidermis

The mechanotransduction of light-touch sensory stimuli is considered to be the main physiological function of epidermal Merkel cells (MCs). Recently, however, MCs have been demonstrated to be also thermo-sensitive, suggesting that their role in skin physiologically extends well beyond mechanosensation. Here, we demonstrate that in healthy human skin epidermal MCs express functional olfactory receptors, namely OR2AT4, just like neighbouring keratinocytes. Selective stimulation of OR2AT4 by topical application of the synthetic odorant, Sandalore®, significantly increased Piccolo protein expression in MCs, as assessed by quantitative immunohistomorphometry, indicating increased vesicle trafficking and recycling, and significantly reduced nerve growth factor (NGF) immunoreactivity within MCs, possibly indicating increased neurotrophin release upon OR2AT4 activation. Live-cell imaging showed that Sandalore® rapidly induces a loss of FFN206-dependent fluorescence in MCs, suggesting OR2AT4-dependent MC depolarization and subsequent vesicle secretion. Yet, in contrast to keratinocytes, OR2AT4 stimulation by Sandalore® altered neither the number nor the proliferation status of MCs. These preliminary ex vivo findings demonstrate that epidermal MCs also exert OR-dependent chemosensory functions in human skin, and invite one to explore whether these newly identified properties are dysregulated in selected skin disorders, for example, in pruritic dermatoses, and if these novel MC functions can be therapeutically targeted to maintain/promote skin health.

Case report: Metastatic Merkel cell carcinoma presenting seven years after loco-regional disease resection of primary tumor with interval in-transit and nodal metastases

Merkel cell carcinoma (MCC) is a rare tumor with a high risk of recurrence after definitive therapy; however, the optimal duration of surveillance is unclear. First recurrences typically occur within 3 years. National guidelines recommend that patients undergo physical examination and imaging for surveillance during this time period. However, the duration of surveillance beyond this is not defined. Here, we describe a case of a patient developing a recurrence of MCC 7 years after the primary diagnosis with interval in-transit and regional lymph node metastases 15 months following the treatment of the primary MCC. Such late recurrences are rare, largely not reported, and the risk factors contributing to late recurrences are not well described. This case highlights the possibility of late recurrences of MCC after an initial in-transit and nodal recurrence and underscores the importance of identifying predictors of recurrence that may better guide the duration of surveillance.

Do Merkel complexes initiate mechanical itch?

Itch is a common sensation which is amenable to disabling patients' life under pathological and chronic conditions. Shared assertion easily limits itch to chemical itch, without considering mechanical itch and alloknesis, its pathological counterpart. However, in recent years, our understanding of the mechanical itch pathway, particularly in the central nervous system, has been enhanced. In addition, Merkel complexes, conventionally considered as tactile end organs only responsible for light touch perception due to Piezo2 expressed by both Merkel cells and SA1 Aβ-fibres - low threshold mechanical receptors (LTMRs) -, have recently been identified as modulators of mechanical itch. However, the tactile end organs responsible for initiating mechanical itch remain unexplored. The consensus is that some LTMRs, either SA1 Aβ- or A∂- and C-, are cutaneous initiators of mechanical itch, even though they are not self-sufficient to finely detect and encode light mechanical stimuli into sensory perceptions, which depend on the entire hosting tactile end organ. Consequently, to enlighten our understanding of mechanical itch initiation, this article discusses the opportunity to consider Merkel complexes as potential tactile end organs responsible for initiating mechanical itch, under both healthy and pathological conditions. Their unsuspected modulatory abilities indeed show that they are tuned to detect and encode light mechanical stimuli leading to mechanical itch, especially as they host not only SA1 Aβ-LTMRs but also A∂- and C-fibres.

Skin cancers under Janus kinase inhibitors: A World Health Organization drug safety database analysis

BACKGROUND

Janus kinase (JAK) inhibitors are targeted therapies with a potential imunomodulatory and anti-inflammatory effect, indicated in various dysimmune pathologies. Skin cancers have been reported to occur in patients treated with JAK inhibitors. However, drug safety in clinical trials did not confirm that risk, but these studies are performed on controlled population and in a limited time of follow up.

OBJECTIVES

The aim of this study is to evaluate in real life condition if a disproportionality signal exists between JAK inhibitors treatment and skin cancers.

METHODS

We performed cases/non cases analysis in VigiBase® (the World Health Organization international database of suspected adverse drug reaction) using information component to search for a disproportionality signal of skin cancers from JAK inhibitor. We extracted all reports of skin cancers from the French Pharmacovigilance database occurring since 1978 up to 31^st December 2019 for the three existing JAK inhibitors on market: ruxolitinib, tofacitinib and baricitinib. Only melanoma, squamous cell carcinoma and Merkel cell carcinoma were analyzed, according to the pathophysiology of these cancers and their link with immunosuppression.

RESULTS

A disproportionality signal was found positive for squamous cell carcinoma with ruxolitinib (IC025=3.92) and tofacitinib (IC025=0.82), for melanoma with ruxolitinib (IC025=0.81) and tofacitinib (IC025=0.74), and Merkel cell carcinoma with ruxolitinib (IC025=4) and tofactinib (IC025=1.01) and only for Merkel cell carcinoma with baricitinib (IC025=0.53). Moreover, Merkel cell carcinoma, a very rare skin cancer more prevalent in immunodepressed patients was particularly represented in our sample and was associated with a significant disproportionality signal with all the studied JAK inhibitors.

CONCLUSION

Our study shows that JAK inhibitors could be associated with an extra risk to develop skin cancers. Could an anti-viral or immunovigilance disruption mechanism brought by JAK inhibitors explain an over-risk with Merkel cell carcinoma, which were notably represented in our sample? Considering pharmacovigilance method limitations, further pharmacoepidemiological studies are required to assess a causal link between JAK inhibitors treatment and skin cancers development.

Partial Gastric Resection for Symptomatic Anemia following Diagnosis of Merkel Cell Carcinoma (MCC) of the Skin with Gastric Metastasis

Merkel Cell Carcinoma (MCC) is a rare dermatologic malignancy with significant morbidity and mortality associated with metastatic disease. In this case, we discuss and extremely rare presentation of MCC with metastasis to the stomach in a patient that presented with profound anemia. Unfortunately, mortality following diagnosis of MCC with gastric metastasis approaches 67% at 4 months based on available published reports. Due to its rarity and high rate of mortality, there is a lack of available research and literature to help guide treatment of this rare presentation of MCC. This case report presents a positive outcome associated with a partial gastrectomy for the treatment of symptomatic MCC with gastric metastasis and continued survival with persistently stable hemoglobin at 12 months.

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.

Merkel cell carcinoma in a young man with AIDS-related Kaposi sarcoma

Merkel cell carcinoma (MCC) is a rare, aggressive primary neuroendocrine carcinoma of the skin that can present in immunocompromised patients. Kaposi sarcoma (KS) is an indolent angioproliferative tumor associated with human herpesvirus 8 (HHV8). The concurrence of both MCC and KS is rare, and there have been limited cases reported in the literature. We present a rare case of concurrent MCC and KS in an immunocompromised patient. To our knowledge, this is the first report of MCC and KS described in the same histopathological specimen. A 37-year-old Black male with a history of recurrent AIDS-related KS involving bilateral lower extremities was evaluated for a tender nodule on the left posterior leg. A punch biopsy was consistent with MCC. Magnetic resonance imaging brain and full-body positron emission tomography/computed tomography (PET/CT) scan were without evidence of distant metastasis. The patient underwent wide local excision with negative margins and completed postoperative radiation therapy. However, he later developed cutaneous metastasis of MCC to the left medial thigh and excision revealed residual MCC with adjacent KS. Treatment is still ongoing with pembrolizumab for both KS and MCC.

Anatomy of the sense of touch in sea otters: Cutaneous mechanoreceptors and structural features of glabrous skin

Sea otters (Enhydra lutris) demonstrate rapid, accurate tactile abilities using their paws and facial vibrissae. Anatomical investigations of neural organization in the vibrissal bed and somatosensory cortex coincide with measured sensitivity, but no studies describe sensory receptors in the paws or other regions of glabrous (i.e., hairless) skin. In this study, we use histology to assess the presence, density, and distribution of mechanoreceptors in the glabrous skin of sea otters: paws, rhinarium, lips, and flipper digits, and we use scanning electron microscopy to describe skin-surface texture and its potential effect on the transduction of mechanical stimuli. Our results confirm the presence of Merkel cells and Pacinian corpuscles, but not Meissner corpuscles, in all sea otter glabrous skin. The paws showed the highest density of Merkel cells and Pacinian corpuscles. Within the paw, relative densities of mechanoreceptor types were highest in the distal metacarpal pad and digits, which suggests that the distal paw is a tactile fovea for sea otters. In addition to the highest receptor density, the paw displayed the thickest epidermis. Rete ridges (epidermal projections into the dermis) and dermal papillae (dermal projections into the epidermis) were developed across all glabrous skin. These quantitative and qualitative descriptions of neural organization and physical features, combined with previous behavioral results, contribute to our understanding of how structure relates to function in the tactile modality. Our findings coincide with behavioral observations of sea otters, which use touch to maintain thermoregulatory integrity of their fur, explore objects, and capture visually cryptic prey.

Sex-Dependent Reduction in Mechanical Allodynia in the Sural-Sparing Nerve Injury Model in Mice Lacking Merkel Cells

Innocuous touch sensation is mediated by cutaneous low-threshold mechanoreceptors (LTMRs). Aβ slowly adapting type I (SAI) neurons constitute one LTMR subtype that forms synapse-like complexes with associated Merkel cells in the basal skin epidermis. Under healthy conditions, these complexes transduce indentation and pressure stimuli into Aβ SAI LTMR action potentials that are transmitted to the CNS, thereby contributing to tactile sensation. However, it remains unknown whether this complex plays a role in the mechanical hypersensitivity caused by peripheral nerve injury. In this study, we characterized the distribution of Merkel cells and associated afferent neurons across four diverse domains of mouse hind paw skin, including a recently described patch of plantar hairy skin. We also showed that in the spared nerve injury (SNI) model of neuropathic pain, Merkel cells are lost from the denervated tibial nerve territory but are relatively preserved in nearby hairy skin innervated by the spared sural nerve. Using a genetic Merkel cell KO mouse model, we subsequently examined the importance of intact Merkel cell-Aβ complexes to SNI-associated mechanical hypersensitivity in skin innervated by the spared neurons. We found that, in the absence of Merkel cells, mechanical allodynia was partially reduced in male mice, but not female mice, under sural-sparing SNI conditions. Our results suggest that Merkel cell-Aβ afferent complexes partially contribute to mechanical allodynia produced by peripheral nerve injury, and that they do so in a sex-dependent manner.SIGNIFICANCE STATEMENT Merkel discs or Merkel cell-Aβ afferent complexes are mechanosensory end organs in mammalian skin. Yet, it remains unknown whether Merkel cells or their associated sensory neurons play a role in the mechanical hypersensitivity caused by peripheral nerve injury. We found that male mice genetically lacking Merkel cell-Aβ afferent complexes exhibited a reduction in mechanical allodynia after nerve injury. Interestingly, this behavioral phenotype was not observed in mutant female mice. Our study will facilitate understanding of mechanisms underlying neuropathic pain.

The Anatomical Distribution of Mechanoreceptors in Mouse Hind Paw Skin and the Influence of Integrin α1β1 on Meissner-Like Corpuscle Density in the Footpads

Afferent neurons and their mechanoreceptors provide critical sensory feedback for gait. The anatomical distribution and density of afferents and mechanoreceptors influence sensory feedback, as does mechanoreceptor function. Electrophysiological studies of hind paw skin reveal the different types of afferent responses and their receptive fields, however, the anatomical distribution of mechanoreceptor endings is unknown. Also, the role of integrin α1β1 in mechanoreceptor function is unclear, though it is expressed by keratinocytes in the stratum basale where it is likely involved in a variety of mechanotransduction pathways and ion channel functionalities. For example, it has been shown that integrin α1β1 is necessary for the function of TRPV4 that is highly expressed by afferent units. The purpose of this study, therefore, was to determine and compare the distribution of mechanoreceptors across the hind paw skin and the footfall patterns of itga1-null and wild type mice. The itga1-null mouse is lacking the integrin α1 subunit, which binds exclusively to the β1 subunit, thus rendering integrin α1β1 nonfunctional while leaving the numerous other pairings of the β1 subunit undisturbed. Intact hind paws were processed, serially sectioned, and stained to visualize mechanoreceptors. Footfall patterns were analyzed as a first step in correlating mechanoreceptor distribution and functionality. Merkel cells and Meissner-like corpuscles were present, however, Ruffini endings and Pacinian corpuscles were not observed. Meissner-like corpuscles were located exclusively in the glabrous skin of the footpads and digit tips, however, Merkel cells were found throughout hairy and glabrous skin. The increased density of Merkel cells and Meissner-like corpuscles in footpads 1 and 3 and Meissner-like corpuscles in footpad 4 suggests their role in anteroposterior balance, while Meissner-like corpuscle concentrations in digits 2 and 5 support their role in mediolateral balance. Finally, a larger density of Meissner-like corpuscles in footpads 3 and 4 in male itga1-null mice compared to wild type controls paves the way for future site-specific single fiber in vivo recordings to provide insight into the role of integrin α1β1 in tactile mechanotransduction.

Follicle-sinus complexes in muzzle skin of domestic and wild animals as diagnostic material for detection of rabies

We previously reported a novel diagnostic method using follicle-sinus complexes (FSCs) in the muzzle skin for postmortem diagnosis of rabies in dogs. However, whether this method works in other animal species remains unclear. Here, FSCs were collected from a wolf, a red fox, 2 bats, and a cat, and examined for the presence of viral antigen, viral mRNA, and viral particles. Viral antigen and viral mRNA were confirmed in Merkel cells (MCs) in FSCs of all species. Electron microscopy performed using only samples from wolf and cat confirmed viral particles in MCs of FSCs. These results suggested that this novel diagnostic method using FSCs might be useful for detection of rabies not only in domestic but also wild animals.

Sentinel Lymph Node Biopsy for Eyelid and Conjunctival Malignancy: A Report by the American Academy of Ophthalmology

PURPOSE

To determine the efficacy and safety of sentinel lymph node biopsy (SLNB) in the management of eyelid and conjunctival malignancy.

METHODS

A literature search was performed in August 2019 and January 2020 for articles published in English in the PubMed and Cochrane Library databases. This search yielded 151 articles that were reviewed for relevancy, of which 27 were deemed to have met the inclusion criteria for this assessment. The data from these articles were abstracted and the articles were rated for strength of evidence by the panel methodologist.

RESULTS

All 27 studies were rated level III, and a total of 197 SLNBs were reported. Diagnoses included conjunctival and eyelid cutaneous melanoma (85 and 42 patients, respectively), sebaceous gland carcinoma (35 patients), squamous cell carcinoma (26 patients), Merkel cell carcinoma (6 patients), pigmented epithelioid melanocytoid tumor (1 patient), mucoepidermoid carcinoma (1 patient), and signet ring carcinoma (1 patient). Tracer was found in regional lymph nodes in 100% of patients in 21 of 27 articles and in 191 of 197 patients overall. The number of lymph nodes removed ranged from 1 to 16, with most ranging from 1 to 5. Tumor-positive lymph nodes were found in 33 of 197 patients (16.8%), prompting recommendations for adjuvant treatments. Survival data were reported for 16 of these patients, with follow-up periods ranging from 3 to 36 months (average, 12.7 months). Fourteen of 16 patients received adjuvant treatments. Nine were alive and well, 1 was alive with metastases, and 6 had died of metastatic disease (including 2 patients who declined additional treatment). False-negative SLNB results were reported in 5 articles involving 9 of 197 procedures (4.6%). Complications were documented in 7 of 27 articles and included transient facial nerve weakness, persistent blue dye staining of the conjunctiva, neck hematoma, and suture abscess.

CONCLUSIONS

Sentinel lymph node biopsy is a promising procedure in patients with eyelid and conjunctival malignancy, and it is useful in identifying sentinel lymph nodes. However, at present, insufficient evidence exists showing that SLNB improves patient outcomes and survival. Recognition of microscopic metastatic disease may prove beneficial in staging and guiding adjuvant therapy.

The Role of Age and Merkel Cell Polyomavirus in Oral Cavity Cancers

The incidence of oral tongue cancer, the majority subsite of oral cavity cancer, is rising among young people with less exposure to tobacco and alcohol. Viral causes have been proposed, including Merkel cell polyomavirus (MCPyV). We evaluated patient and tumor characteristics among 126 incident oral cavity cancers (OCCs). Consistent with generational norms, younger patients had less exposure to tobacco and a greater number of oral sexual partners than older OCCs. In addition, younger patients were more likely to present at an earlier stage and with cancer arising from the oral tongue (each P < .05). A subset of 44 cases was centrally tested for MCPyV large T antigen expression by immunohistochemistry. In the presence of controls, none of the tumors expressed MCPyV. These findings exclude consideration of MCPyV as an etiologic factor in OCC and may generate hypotheses for future examinations of the factors underlying the rise in oral tongue cancers.

Triple collision tumor comprising Merkel cell carcinoma with an unusual immunophenotype, squamous cell carcinoma in situ, and basal cell carcinoma

Merkel cell carcinoma (MCC) is a rare, aggressive primary cutaneous neuroendocrine cancer which almost always exhibits the cytokeratin (CK)20+/thyroid transcription factor (TTF)-1- immunophenotype. MCC may occur concurrently with squamous cell carcinoma, Bowen disease, and/or basal cell carcinoma (BCC), with some evidence that MCCs which occur in conjunction with other neoplasms exhibit different immunophenotypes compared to pure MCC cases. We present a case of CK20-/TTF-1+ MCC concurrent with Bowen disease and BCC, and discuss possible differences in the pathogenesis of pure vs combined MCC. We also review the literature for this unusual immunophenotype, noting that most cases occur in combined MCC.

Immunotherapy for skin cancer

Among all tumor types, skin cancers are profoundly sensitive to immunotherapy. Indeed, the recently reported response rates for anti-PD-1 (anti-programmed-death 1) therapy for cutaneous malignant melanomas (MM), Merkel cell carcinomas, basal cell carcinomas, cutaneous squamous cell carcinomas and Kaposi sarcomas are all above 40%. This unique immunogenicity renders skin cancers as a paradigm for tumor-immune interactions and is driven by high mutational burdens, over-expressed tumor antigens and/or viral antigens. However, despite the clear demonstration of immunologic cure of skin cancer in some patients, most tumors develop either early (primary) or late (adaptive) resistance to immunotherapy. Resistance mechanisms are complex, and include contributions of tumor cell-intrinsic, T cell and microenvironment factors that have been recently further elucidated with the advent of single-cell technologies. This review will focus on the exciting progress with immunotherapy for skin cancers to date, and also our current understanding of the mechanisms of resistance to immunotherapy.

Avelumab Immunotherapy: Management of Adverse Events Associated With New Treatment for Merkel Cell Carcinoma

BACKGROUND

Metastatic Merkel cell carcinoma (mMCC) is a rare skin cancer with poor prognosis. Avelumab is the first approved treatment option for patients with mMCC. Immune checkpoint inhibitors, such as avelumab, are associated with unique toxicities that can be effectively addressed with prompt recognition and appropriate management.

OBJECTIVES

This article discusses the use of avelumab for the treatment of mMCC and management of associated toxicities.

METHODS

Literature on mMCC disease state and clinical trial data for avelumab were reviewed.

FINDINGS

Avelumab has been investigated in patients with mMCC either following disease progression after one or more prior lines of chemotherapy or no prior systemic therapy. These patients experience clinically meaningful benefit. About 70% of patients receiving avelumab experience treatment-related adverse events. Given the limited benefit of chemotherapy, managing symptoms related to avelumab is key to administering this effective treatment to patients with mMCC.

Patterns of distant metastases in 215 Merkel cell carcinoma patients: Implications for prognosis and surveillance

Approximately one‐third of Merkel cell carcinoma (MCC) patients eventually develop distant metastatic disease. Little is known about whether the location of the primary lesion is predictive of initial distant metastatic site, or if survival likelihood differs depending on the metastatic site. Such data could inform imaging/surveillance practices and improve prognostic accuracy. Multivariate and competing‐risk analyses were performed on a cohort of 215 MCC patients with distant metastases, 31% of whom had two or more initial sites of distant metastasis. At time of initial distant metastasis in the 215 patients, metastatic sites (n = 305) included non‐regional lymph nodes (present in 41% of patients), skin/body wall (25%), liver (23%), bone (21%), pancreas (8%), lung (7%), and brain (5%). Among the 194 patients who presented with MCC limited to local or regional sites (stage I‐III) but who ultimately developed distant metastases, distant progression occurred in 49% by 1 year and in 80% by 2 years following initial diagnosis. Primary MCC locations differed in how likely they were to metastasize to specific organs/sites (P < .001). For example, liver metastases were far more likely from a head/neck primary (43% of 58 patients) versus a lower limb primary (5% of 39 patients; P < .0001). Skin‐only distant metastasis was associated with lower MCC‐specific mortality as compared to metastases in multiple organs/sites (HR 2.7; P = .003), in the liver (HR 2.1; P = .05), or in distant lymph nodes (HR 2.0; P = .045). These data reflect outcomes before PD1‐pathway inhibitor availability, which may positively impact survival. In conclusion, primary MCC location is associated with a pattern of distant spread, which may assist in optimizing surveillance. Because it is linked to survival, the site of initial distant metastasis should be considered when assessing prognosis.

The morphology, size and density of the touch dome in human hairy skin by scanning electron microscopy

The touch domes of mammalian hairy skin are mechanoreceptors characterized by the accumulation of Merkel cell-neurite complexes at the epidermal base. In this study, we examined the shape, size, and density of the touch dome of human skin of the forearm and the abdomen through scanning electron microscopy (SEM). Human skin samples were obtained from donated bodies, as well as a patient who underwent biopsy. Skin pieces were treated with a KOH-collagenase method for the separation of the epidermis from the dermis. The basal surface of the separated epidermis was then observed using SEM. The touch dome was clearly determined as a concave area bordered by a thick epidermal ridge, where neural components accumulated. The touch dome was rather independent from hair follicles, although they were sometimes located beside the touch dome. The average size and density of the touch dome were 0.06 mm2 and 3.82 cm2 in the forearm, and 0.10 mm2 and 1.30 cm2 in the abdomen, respectively. Our results suggested that the regional difference in size and density of the touch dome might be related to the sensation's sensitivity as touch spots in human hairy skin.

Cutaneous nociception: Role of keratinocytes

Recent years have brought an enhanced understanding of keratinocyte contribution to cutaneous nociception. While intra-epidermal nerve endings were classically considered as the exclusive transducers of cutaneous noxious stimuli, it has now been demonstrated that epidermal keratinocytes can initiate nociceptive responses, like Merkel cells do for the innocuous mechanotransduction. In the light of recent in vivo findings, this article outlines this paradigm shift that points to a not yet considered population of sensory epidermal cells.

Merkel Cells Release Glutamate Following Mechanical Stimulation: Implication of Glutamate in the Merkel Cell-Neurite Complex

Merkel cells (MCs) have been proposed to form a part of the MC-neurite complex with sensory neurons through synaptic contact. However, the detailed mechanisms for intercellular communication between MCs and neurons have yet to be clarified. The present study examined the increases in intracellular free Ca²⁺ concentration ([Ca²⁺]_i) induced by direct mechanical stimulation of MCs. We also measured [Ca²⁺]_i in the trigeminal ganglion neurons (TGs) following direct mechanical stimulation to the MCs in an MC-TGs coculture. The MCs were isolated from hamster buccal mucosa, while TGs were isolated from neonatal Wistar rats. Both cell populations showed depolarization-induced [Ca²⁺]_i. Direct mechanical stimulation to MCs increased [Ca²⁺]_i, showing stimulation strength dependence. In the MC-TGs coculture, the application of direct mechanical stimulation to MCs resulted in increased [Ca²⁺]_i in the TGs. These changes were significantly suppressed by antagonists of glutamate-permeable anion channels (4,4′-diisothiocyanato-2,2′-stilbenedisulfonic acid; DIDS), and non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptors (MK801). Apyrase, an ATP-degrading enzyme, and suramin, a non-selective P2 purinergic receptor antagonist, did not exert inhibitory effects on these [Ca²⁺]_i increases in the TGs following MC stimulation. These results indicated that MCs are capable of releasing glutamate, but not ATP, in response to cellular deformation by direct mechanical stimulation. The released glutamate activates the NMDA receptors on TGs. We suggest that MCs act as mechanoelectrical transducers and establish synaptic transmission with neurons, through the MC-neurite complex, to mediate mechanosensory transduction.

Diffuse lichen planus-like keratoses and clinical pseudo-progression associated with avelumab treatment for Merkel cell carcinoma, a case report

Background

Avelumab is an anti-programmed cell death ligand 1 (PD-L1) antibody approved for treatment of Merkel cell carcinoma (MCC) and locally advanced or metastatic urothelial carcinoma. It shares a similar side effect profile to other immune checkpoint inhibitors, including immune-related adverse reactions in the skin. These adverse skin reactions can present as a morbilliform exanthem, lichenoid dermatitis, vitiligo, autoimmune bullous disorder, among others.

Case presentation

We describe a patient with advanced MCC successfully treated with avelumab who developed acute onset diffuse lichen planus-like keratoses (LPLK) at sites of existing seborrheic keratoses (SK) and lentigines. Histopathology of an affected SK revealed papillomatous epidermal hyperplasia with lichenoid interface changes, numerous dyskeratotic keratinocytes and intermittent hypergranulosis. The findings resembled lichen planus (LP) arising in an SK. Onset of the skin symptoms corresponded with an inflammatory cancer response (clinical pseudo-progression), and the eruption improved as overall tumor burden decreased. The patient’s pruritus was treated with topical steroids and cyrotherapy for individual symptomatic lesions.

Conclusion

Diffuse LPLK is a distinct immune-related reaction pattern associated with PD-L1/PD-1 checkpoint blockade. This is an important side effect to be aware of as LPLK frequently mimic keratinocytic neoplasms. Further observation is needed to assess the prevalence and significance of this immune therapy-associated adverse reaction.

A Report of 13 Cases of Merkel Cell Carcinoma: Single-Center Experience and Review of the Literature

Background

There is limited data knowledge of Merkel cell carcinoma (MCC) in Turkey aside from a few case reports.

Objective

The aim of this study was to describe the clinical characteristics, demographic features, therapeutic parameters, and outcome of primary cutaneous MCC cases from Turkey.

Methods

Digital medical records of the 13 MCC patients who were followed-up at a tertiary referral center were retrospectively analyzed. Clinic, demographic, tumor characteristics, and survival of the patients were retrieved.

Results

Most of our patients were elderly. Female predominance was noticed. The most common primary site of the tumors was the lower extremities. The overall survival was 42 months, 68% at first year, 68% at third years, and 29% at fifth years.

Conclusion

This is the first largest report from Turkish population with female predominance, and lower extremity tendency.

Upper eyelid Merkel cell carcinoma treated with neoadjuvant chemotherapy and surgical excision

Merkel cell carcinoma is a rare cutaneous carcinoma, featured by an aggressive clinical course and a mortality rate of 28% at 2 years. A 71-year-old female was affected by a 4.1-cm-wide locally advanced Merkel cell carcinoma of the upper eyelid, previously misdiagnosed as chalazion, with involvement of the extraocular muscles. Although the tumor showed a macroscopic spontaneous regression in size after the incisional biopsy, the mass was treated with neoadjuvant chemotherapy and surgical excision. Good functional and aesthetic result with preservation of the eyeball and absence of tumor recurrence were achieved at 3-year follow-up. In our experience, the combination of the inflammatory cascade due to the incisional biopsy and neoadjuvant chemotherapy led to the regression of a locally advanced large Merkel cell carcinoma of the eyelid.

Adhesive pyramidal thorn patches provide pain relief to athletes

Pain in athletes is ideally treated without systemic medicine. Therefore, complementary and alternative medicine, including patch treatments, is often used. The physiologic mechanisms of pain relief produced by patch treatment, however, are not well elucidated. In the present study, we introduce a pyramidal thorn (PT) patch that we developed, demonstrate the effects of this PT patch for the treatment of various types of pain in 300 subjects, and suggest a physiologic mechanism for the pain relief effects. One treatment with the PT patch effectively relieved pain in almost half the subjects evaluated. Except for pain generated deeply under the skin, such as low-back pain, pain was eliminated within four treatments with the PT patch in almost all of the subjects. Interestingly, the pain-sensing region moved along the nerve fibers after each trial. Further, patches without PT also provided some pain relief. We considered that this effect was due to hair deflection on the skin; that is, adhesion of the PT patch activates Merkel cells directly as well as Merkel cell-neurite complexes around the hair follicles by deflecting the hair follicles, whereas adhesion of a patch without PT only activates the Merkel cell-neurite complexes. In any case, patch adhesion stimulates Aβ fibers to alleviate pain. Finally, we found that the pain threshold is increased by electric stimulation, suggesting that the gentle adhesion of a PT patch would be more effective. To our knowledge, this is the first study to demonstrate physiologically the validity of an adherent patch for pain relief.

Nonmelanoma Skin Cancer

This article reviews the most common nonmelanoma skin cancers affecting the head and neck region. Although the most common of these malignancies rarely result in mortality, local morbidity caused by the tumors and their extirpation cannot be underestimated. Complete tumor extirpation with pathologically confirmed negative margins is the gold standard. Regional and distant metastases are rare, but must be treated appropriately should they occur. Although reconstructive surgery can be life changing for the patients and rewarding for the clinicians, it behooves the treating surgeons to remain true to oncologic principles above all else.

Merkel Cells: A Collective Review of Current Concepts

Merkel cells (MCs) constitute a very unique population of postmitotic cells scattered along the dermo-epidermal junction. These cells that have synaptic contacts with somatosensory afferents are regarded to have a pivotal role in sensory discernment. Several concerns exist till date as to their origin, multiplication, and relevance in skin biology. The article, a collective review of literature extracted from PubMed search and dermatology books, provides novel insights into the physiology of MCs and their recent advances.

Follicle sinus complexes (FSCs) in muzzle skin as postmortem diagnostic material of rabid dogs

Recently, we reported that follicle-sinus complexes (FSCs) in the muzzle skin are useful for postmortem diagnosis of rabid dogs. Here, we compared the sensitivity and specificity of detecting the viral antigen in the brain and FSCs of 226 suspected rabid dogs, and assessed whether the FSC harbored the virus genome and particles. The viral antigen was detected in 211 of 226 samples with 100% sensitivity and specificity. Viral RNA and particles were observed in the cytoplasm of Merkel cells (MCs). These results suggest that MCs are targets of virus infection and FSCs are useful material for diagnosing rabies.

A novel report of a primary Merkel cell carcinoma lesion in the nasal vestibule

Merkel cell carcinoma (MCC) accounts for less than 1% of cutaneous malignancies. As the lesion may mimic benign entities, clinicians' differential should include rare entities to improve outcomes by early intervention. We present a case of primary MCC in the nasal vestibule requiring partial rhinectomy, suprahyoid lymphadenectomy, and radiation therapy.

Merkel cells in extraocular sebaceous carcinoma

INTRODUCTION

Mature sebaceous glands do not contain Merkel cells. Neither do sebaceous tumors in the vast majority of cases. Recently, however, it was showed that rare sebaceous adenomas with a carcinoid-like or labyrinthine pattern can contain intratumoral Merkel cells. Our purpose in this study is to examine for the presence of Merkel cells in extraocular sebaceous carcinomas.

METHODS

Nineteen cases of extraocular sebaceous carcinoma were retrospectively studied with cytokeratin 20.

RESULTS

One out of 19 cases (5.3%) contained Merkel cells in the basal layers of the tumoral nests of a sebaceous carcinoma from the cheek of a 76-year-old woman.

CONCLUSIONS

Merkel cells are rarely evident in extraocular sebaceous carcinoma, and therefore, their evidence does not exclude this diagnosis.

Multidimensional, quantitative assessment of PD-1/PD-L1 expression in patients with Merkel cell carcinoma and association with response to pembrolizumab

Background

We recently reported a 56% objective response rate in patients with advanced Merkel cell carcinoma (MCC) receiving pembrolizumab. However, a biomarker predicting clinical response was not identified.

Methods

Pretreatment FFPE tumor specimens (n = 26) were stained for CD8, PD-L1, and PD-1 by immunohistochemistry/immunofluorescence (IHC/IF), and the density and distribution of positive cells was quantified to determine the associations with anti-PD-1 response. Multiplex IF was used to test a separate cohort of MCC archival specimens (n = 16), to identify cell types expressing PD-1.

Results

Tumors from patients who responded to anti-PD-1 showed higher densities of PD-1+ and PD-L1+ cells when compared to non-responders (median cells/mm², 70.7 vs. 6.7, p = 0.03; and 855.4 vs. 245.0, p = 0.02, respectively). There was no significant association of CD8+ cell density with clinical response. Quantification of PD-1+ cells located within 20 μm of a PD-L1+ cell showed that PD-1/PD-L1 proximity was associated with clinical response (p = 0.03), but CD8/PD-L1 proximity was not. CD4+ and CD8+ cells in the TME expressed similar amounts of PD-1.

Conclusions

While the binomial presence or absence of PD-L1 expression in the TME was not sufficient to predict response to anti-PD-1 in patients with MCC, we show that quantitative assessments of PD-1+ and PD-L1+ cell densities as well as the geographic interactions between these two cell populations correlate with clinical response. Cell types expressing PD-1 in the TME include CD8+ T-cells, CD4+ T-cells, T_regs, and CD20+ B-cells, supporting the notion that multiple cell types may potentiate tumor regression following PD-1 blockade.

Electronic supplementary material

The online version of this article (10.1186/s40425-018-0404-0) contains supplementary material, which is available to authorized users.

Vesicular glutamate transporter isoforms: The essential players in the somatosensory systems

In nervous system, glutamate transmission is crucial for centripetal conveyance and cortical perception of sensory signals of different modalities, which necessitates vesicular glutamate transporters 1-3 (VGLUT 1-3), the three homologous membrane-bound protein isoforms, to load glutamate into the presysnaptic vesicles. These VGLUTs, especially VGLUT1 and VGLUT2, selectively label and define functionally distinct neuronal subpopulations at each relay level of the neural hierarchies comprising spinal and trigeminal sensory systems. In this review, by scrutinizing each structure of the organism's fundamental hierarchies including dorsal root/trigeminal ganglia, spinal dorsal horn/trigeminal sensory nuclear complex, somatosensory thalamic nuclei and primary somatosensory cortex, we summarize and characterize in detail within each relay the neuronal clusters expressing distinct VGLUT protein/transcript isoforms, with respect to their regional distribution features (complementary distribution in some structures), axonal terminations/peripheral innervations and physiological functions. Equally important, the distribution pattern and characteristics of VGLUT1/VGLUT2 axon terminals within these structures are also epitomized. Finally, the correlation of a particular VGLUT isoform and its physiological role, disclosed thus far largely via studying the peripheral receptors, is generalized by referring to reports on global and conditioned VGLUT-knockout mice. Also, researches on VGLUTs relating to future direction are tentatively proposed, such as unveiling the elusive differences between distinct VGLUTs in mechanism and/or pharmacokinetics at ionic/molecular level, and developing VGLUT-based pain killers.

Fatal enteric plexus neuropathy after one dose of ipilimumab plus nivolumab: a case report

Background

Immune checkpoint inhibitors (ICIs) are the treatment of choice for several cancers and can be associated with remarkable clinical benefit, but can also cause serious immune-related adverse events (irAEs). Management of rare and severe irAEs is challenged by an incomplete knowledge of their natural history and pathogenetic mechanisms. We report a case of fatal acute-onset gastro-intestinal (GI) hypomotility from myenteric plexus neuropathy following a single dose of ipilimumab plus nivolumab given for treatment of Merkel cell carcinoma (MCC).

Case presentation

A 66-year-old man with recurrent metastatic MCC involving several organs (liver, bones and disseminated retroperitoneal lymphadenopathy) developed profound pharyngeal dysphagia and ileus that started 7 days after receiving a single administration of combination immune checkpoint blockade consisting of nivolumab (3 mg/kg) and low-dose ipilimumab (1 mg/kg). A swallowing study showed oropharyngeal dysfunction and aspiration. Imaging studies were consistent with diffuse intestinal paresis. An extensive work-up did not reveal obvious causes of these symptoms, and enteric plexopathy was suspected. Empiric immune suppressive therapy was initiated urgently. Despite an escalating immunosuppressive regimen that included high dose steroids, tacrolimus and therapeutic plasma exchange, no improvement in GI motility was seen and the patient suffered repeated episodes of aspiration. Seven weeks after the onset of GI hypomotility, the patient succumbed to sepsis from intestinal perforations. At autopsy, histologic specimens obtained from the entire GI tract (pharynx to rectum) showed near complete loss of ganglion cells within the myenteric and submucosal plexuses. An associated inflammatory infiltrate was not seen, suggesting a ‘burned out’ phase of illness. C4d complement deposition was found at the ganglionic sites, suggesting antibody-mediated pathogenesis. Remarkably, at sites of previously suspected Merkel cell metastases, no residual viable Merkel cell carcinoma was identified.

Conclusions

GI-tract paresis due to myenteric neuritis is a rarely reported toxicity of ICIs. Because the window of reversibility is likely to be very brief, quick and decisive interventions are warranted. Subtle functional and anatomic perturbations of the myenteric nervous system from the use of ICIs may be more prevalent than realized and should be suspected and addressed in both clinical and investigational settings.

Merkel cell carcinoma and the challenge in its approach: a review based on a clinical context of immunosuppression

Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine cancer with high rate to local relapse and metastasis. Its connection to immunosuppression is well known, with reported association to human immunodeficiency virus (HIV).

The authors present an 87-year-old woman, infected by HIV type 2 at advanced stage of the disease, whom presented a painless papule on left cheek in 2011. After its total excision, the histopathology confirmed MCC “in situ,” with no regional or distant metastases. Simultaneously, she revealed a viral load of 2220 copies/mL and 224 CD4/mm³. Five months later, the patient presented a local and distance relapse with an aggressive behavior and positive regional lymph node. Stage IV disease was confirmed due to presence of liver metastases. Concurrently to the relapse, it was detected low CD4 levels.

In our multidisciplinary team decision meeting, it has been decided conservative treatment due to low Karnofsky status, comorbidities, and stage of disease.

PRC1 Fine-tunes Gene Repression and Activation to Safeguard Skin Development and Stem Cell Specification

Polycomb repressive complexes (PRCs) 1 and 2 are essential chromatin regulators of cell identity. PRC1, a dominant executer of Polycomb-mediated control, functions as multiple sub-complexes that possess catalytic-dependent H2AK119 mono-ubiquitination (H2AK119ub) and catalytic-independent activities. Here, we show that, despite its well-established repressor functions, PRC1 binds to both silent and active genes. Through in vivo loss-of-function studies, we show that global PRC1 function is essential for skin development and stem cell (SC) specification, whereas PRC1 catalytic activity is dispensable. Further dissection demonstrated that both canonical and non-canonical PRC1 complexes bind to repressed genes, marked by H2AK119ub and PRC2-mediated H3K27me3. Interestingly, loss of canonical PRC1, PRC1 catalytic activity, or PRC2 leads to expansion of mechanosensitive Merkel cells in neonatal skin. Non-canonical PRC1 complexes, however, also bind to and promote expression of genes critical for skin development and SC formation. Together, our findings highlight PRC1's diverse roles in executing a precise developmental program.

The association between geographic location and incidence of Merkel cell carcinoma in comparison to melanoma: An international assessment

AIM

The aim of this article was to provide worldwide, population-based incidence rates for Merkel cell carcinoma (MCC).

METHODS

We included 11,576 cases from 20 countries for time trend analyses (1990-2007) and 11,028 cases (2.5 billion person-years) from 21 countries for the period 2003-2007 extracted from Cancer Incidence in Five Continents. We computed age-standardised incidence rates (World Standard population) per million person years and sex ratios of these rates. We estimated annual percentage changes (EAPCs) of the incidence and studied the association between geographic latitude and MCC incidence. We examined the body site distribution of MCC.

FINDINGS

In the majority of populations, the incidence has increased over time (EAPC, men 2.0-21.0%; women 1.6-27.2%). Rate differences between 1995 and 2007 were typically small (men: 0.8-2.2; women: 0.2-1.7). The incidence was relatively stable in some populations (men: U.S. blacks, Japan, Norway, Denmark; women: Denmark, Norway, Sweden). Incidences from 2003 to 2007 were highest in Australia, New Zealand, the United States and Israel among men and in New Zealand, Australia, Ireland and the Netherlands among women. The incidence of MCC and melanoma among white non-Hispanic males in North America was positively associated with living closer to the equator. The proportion of MCC on the head was higher with advanced age. The head was a less likely primary site among blacks as compared with any other ethnicity.

INTERPRETATION

Several countries showed increases in MCC incidence among white non-Hispanics over time. Latitude closer to the equator was associated with the MCC incidence in North American men, but barely in women, possibly due to occupational sunlight exposure patterns.

Treatment of a Patient with Merkel Cell Skin Carcinoma Using Radiation Therapy - A Case Report

BACKGROUND:

Merkel cell carcinoma (MCC) is a rare, very aggressive tumour. The pathogenesis remains unclear, but UV radiation, immunosuppression, and the presence of Merkel cell polyomavirus in the tumour genome appear to have a key role. Merkel cell carcinoma is a highly aggressive tumour that often has a lethal end.

CAS REPORT:

A patient at 93 years of age comes for an examination by a dermatologist due to a rapidly growing nodular tumour growth in the forehead area. A tumour was about 3 cm in size. It had no signs of basal-cell carcinoma, no arborising vascularisation, no pigmentations on dermoscopy. Clinically, an eventual Merkel cell carcinoma was considered for the patient, but other primary skin tumours had to be excluded, as well as the possibility that regarding the patient’s age, it may be a metastatic deposit. A skin biopsy was performed, as well as H-E examination and immunohistochemical analyses (positive CD56, positivity of neuroendocrine markers synaptophysin, chromogranin) which were in favour of Merkel cell carcinoma of the skin. After setting the diagnosis, our patient was treated with therapy which led to a complete withdrawal of a tumour. However, after 3 months the patient had repeated relapse of a tumour at the same site on the forehead and metastases in the retroauricular lymph nodes bilaterally. It shows that the radiotherapy as monotherapy has a great effect on the removal of the tumour formation, but unfortunately, it has no impact on lesion recurrence. It is also compatible with the literature data.

CONCLUSION:

In many adult patients, as our case suggests, radiotherapy could be a good palliative treatment opportunity that should be considered, as well as a combination of radiation therapy with other oncologic therapeutic options.

Merkel Cell Polyomavirus Small T Antigen Drives Cell Motility via Rho-GTPase-Induced Filopodium Formation

Cell motility and migration is a complex, multistep, and multicomponent process intrinsic to progression and metastasis. Motility is dependent on the activities of integrin receptors and Rho family GTPases, resulting in the remodeling of the actin cytoskeleton and formation of various motile actin-based protrusions. Merkel cell carcinoma (MCC) is an aggressive skin cancer with a high likelihood of recurrence and metastasis. Merkel cell polyomavirus (MCPyV) is associated with the majority of MCC cases, and MCPyV-induced tumorigenesis largely depends on the expression of the small tumor antigen (ST). Since the discovery of MCPyV, a number of mechanisms have been suggested to account for replication and tumorigenesis, but to date, little is known about potential links between MCPyV T antigen expression and the metastatic nature of MCC. Previously, we described the action of MCPyV ST on the microtubule network and how it impacts cell motility and migration. Here, we demonstrate that MCPyV ST affects the actin cytoskeleton to promote the formation of filopodia through a mechanism involving the catalytic subunit of protein phosphatase 4 (PP4C). We also show that MCPyV ST-induced cell motility is dependent upon the activities of the Rho family GTPases Cdc42 and RhoA. In addition, our results indicate that the MCPyV ST-PP4C interaction results in the dephosphorylation of β₁ integrin, likely driving the cell motility pathway. These findings describe a novel mechanism by which a tumor virus induces cell motility, which may ultimately lead to cancer metastasis, and provides opportunities and strategies for targeted interventions for disseminated MCC.

IMPORTANCE Merkel cell polyomavirus (MCPyV) is the most recently discovered human tumor virus. It causes the majority of cases of Merkel cell carcinoma (MCC), an aggressive skin cancer. However, the molecular mechanisms implicating MCPyV-encoded proteins in cancer development are yet to be fully elucidated. This study builds upon our previous observations, which demonstrated that the MCPyV ST antigen enhances cell motility, providing a potential link between MCPyV protein expression and the highly metastatic nature of MCC. Here, we show that MCPyV ST remodels the actin cytoskeleton, promoting the formation of filopodia, which is essential for MCPyV ST-induced cell motility, and we also implicate the activity of specific Rho family GTPases, Cdc42 and RhoA, in these processes. Moreover, we describe a novel mechanism for the activation of Rho-GTPases and the cell motility pathway due to the interaction between MCPyV ST and the cellular phosphatase catalytic subunit PP4C, which leads to the specific dephosphorylation of β1 integrin. These findings may therefore provide novel strategies for therapeutic intervention for disseminated MCC.

Insulinoma-associated 1: A novel nuclear marker in Merkel cell carcinoma (cutaneous neuroendocrine carcinoma)

Merkel cell carcinoma (MCC) is a rare, clinically aggressive, cutaneous neuroendocrine (NE) neoplasm. As a tumor with small, round, blue cells, the histologic differential diagnosis for MCC can include melanoma, metastatic small cell carcinoma (SCC), nodular hematopoietic tumors, basal cell carcinoma (BCC), atypical variants of squamous carcinoma and the uncommon occurrence of primary cutaneous Ewing sarcoma. In cases with atypical histology or without the classic immunophenotype, the diagnosis can be challenging. Ultimately, immunohistochemistry (IHC) is essential to the definitive diagnosis of MCC and in difficult cases, the diagnosis may hinge entirely on the immunophenotype of the tumor cells. Insulinoma-associated 1 (INSM1) is a transcription factor expressed in tissues undergoing terminal NE differentiation. As a nuclear protein tied to both differentiation and the cell cycle, INSM1 may offer additional utility in comparison to traditional, cytoplasmic markers of NE differentiation.

Developing a sense of touch

The sensation of touch is mediated by mechanosensory neurons that are embedded in skin and relay signals from the periphery to the central nervous system. During embryogenesis, axons elongate from these neurons to make contact with the developing skin. Concurrently, the epithelium of skin transforms from a homogeneous tissue into a heterogeneous organ that is made up of distinct layers and microdomains. Throughout this process, each neuronal terminal must form connections with an appropriate skin region to serve its function. This Review presents current knowledge of the development of the sensory microdomains in mammalian skin and the mechanosensory neurons that innervate them.

Touch Receptors Undergo Rapid Remodeling in Healthy Skin

Sensory tissues exposed to the environment, such as skin, olfactory epithelia, and taste buds, continuously renew; therefore, peripheral neurons must have mechanisms to maintain appropriate innervation patterns. Although somatosensory neurons regenerate after injury, little is known about how these neurons cope with normal target organ changes. To elucidate neuronal plasticity in healthy skin, we analyzed the structure of Merkel-cell afferents, which are gentle touch receptors, during skin remodeling that accompanies mouse hair-follicle regeneration. The number of Merkel cells is reduced by 90% and axonal arbors are simplified during active hair growth. These structures rebound within just days. Computational modeling predicts that Merkel-cell changes are probabilistic, but myelinated branch stability depends on Merkel-cell inputs. Electrophysiology and behavior demonstrate that tactile responsiveness is less reliable during active growth than in resting skin. These results reveal that somatosensory neurons display structural plasticity at the cost of impairment in the reliability of encoding gentle touch.

Reviewing the current evidence supporting early B-cells as the cellular origin of Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a highly malignant skin cancer characterized by early metastases and poor survival. Although MCC is a rare malignancy, its incidence is rapidly increasing in the U.S. and Europe. The discovery of the Merkel cell polyomavirus (MCPyV) has enormously impacted our understanding of its etiopathogenesis and biology. MCCs are characterized by trilinear differentiation, comprising the expression of neuroendocrine, epithelial and B-lymphoid lineage markers. To date, it is generally accepted that the initial assumption of MCC originating from Merkel cells (MCs) is unlikely. This is owed to their post-mitotic character, absence of MCPyV in MCs and discrepant protein expression pattern in comparison to MCC. Evidence from mouse models suggests that epidermal/dermal stem cells might be of cellular origin in MCC. The recently formulated hypothesis of MCC originating from early B-cells is based on morphology, the consistent expression of early B-cell lineage markers and the finding of clonal immunoglobulin chain rearrangement in MCC cells. In this review we elaborate on the cellular ancestry of MCC, the identification of which could pave the way for novel and more effective therapeutic regimens.

Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) encompasses neuroendocrine carcinomas primary to skin and occurs most commonly in association with clonally integrated Merkel cell polyomavirus with related retinoblastoma protein sequestration or in association with UV radiation-induced alterations involving the TP53 gene and mutations, heterozygous deletion, and hypermethylation of the Retinoblastoma gene. Molecular genetic signatures may provide therapeutic guidance. Morphologic features, although patterned, are associated with predictable diagnostic pitfalls, usually resolvable by immunohistochemistry. Therapeutic options for MCC, traditionally limited to surgical intervention and later chemotherapy and radiation, are growing, given promising early results of immunotherapeutic regimens.

Update from the 4th Edition of the World Health Organization Classification of Head and Neck Tumours: What Is New in the 2017 WHO Blue Book for Tumors and Tumor-Like Lesions of the Neck and Lymph Nodes

The World Health Organization (WHO) 2017 Classification of Head and Neck Tumors ("Blue Book") will now include a new chapter on tumors and tumor-like lesions of the neck and lymph nodes, which was not included in the previous edition. Tumors and tumor-like lesions, including a variety of cysts and metastases, can arise in any component in the neck, including soft tissue, lymph nodes, and developmental remnants. The pathology and clinical features of metastatic carcinoma of unknown primary in the head and neck has changed dramatically in the last several years. Many of these tumors which were previously diagnosed as unknown primary are now identified as oropharyngeal and nasopharyngeal carcinomas related to human papillomavirus (HPV), less commonly to Epstein-Barr virus (EBV) and occasionally even to Merkel cell polyomavirus. Many unusual features can arise in these metastases, such as undifferentiated morphology, extensive cystic change with central degeneration, gland formation, and even ciliated cells. Rarely, carcinoma in the neck can arise in association with a heterotopic tissue, primarily thyroid or salivary gland tissue. Tumor-like lesions include branchial cleft cysts, thyroglossal duct cyst, dermoid and teratoid cyst, and ranula. Pathologists should be familiar with the diagnostic features and clinicopathologic corrections of these neck lesions in order to correctly diagnosis them and to provide for proper clinical management. This article will briefly describe the pathologic and clinical features of these entities as they are covered in the new 2017 Blue Book.