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Deficiency of adenosine deaminase type 2 (DADA2) is an autosomal recessive monogenic autoinflammatory syndrome that is classically characterised by polyarteritis nodosa, systemic vasculitis and stroke. The spectrum of disease manifestations has broadened to encompass a range of cutaneous, vascular and haematological manifestations. We report a novel association in two sisters with heterozygous p.R169G/p.M309l mutations in ADA2 with low serum ADA2 activity who both presented similarly with clinical and histological features consistent with histiocytoid Sweet syndrome.

Melanocytic lesions in the nail apparatus are often challenging. Both subungual melanomas (SUM) and blue naevus of the nail are very rare. Occasionally, melanomas may mimic blue naevus histologically. Benign and malignant blue melanocytic lesions are commonly associated with G protein mutations, a distinct abnormality not associated with conventional subungual melanomas. We describe the clinical, histological and immunohistochemical features of nine cases of SUM with blue naevus-like morphological features. Mutations in exon 4 and 5 of GNAQ and GNA11 were investigated in two cases, which showed no mutations. RNA-seq of one case revealed unknown mutations along with mutations in ATM, METK and ARID1A. Our study delineates a variant of SUM that mimics blue naevus. Awareness of this pitfall is important when evaluating heavily pigmented lesions around the nail in order to avoid misdiagnosis. Appropriate sampling of subungual lesions and clinicopathological correlation are paramount to reach the correct diagnosis.

HPV42 consensus genomes.

The skin is exposed to viral pathogens, but whether they contribute to the oncogenesis of skin cancers has not been systematically explored. Here we investigated 19 skin tumor types by analyzing off-target reads from commonly available next-generation sequencing data for viral pathogens. We identified human papillomavirus 42 (HPV42) in 96% (n = 45/47) of digital papillary adenocarcinoma (DPA), an aggressive cancer occurring on the fingers and toes. We show that HPV42, so far considered a nononcogenic, “low-risk” HPV, recapitulates the molecular hallmarks of oncogenic, “high-risk” HPVs. Using machine learning, we find that HPV-driven transformation elicits a germ cell–like transcriptional program conserved throughout all HPV-driven cancers (DPA, cervical carcinoma, and head and neck cancer). We further show that this germ cell–like transcriptional program, even when reduced to the top two genes (CDKN2A and SYCP2), serves as a fingerprint of oncogenic HPVs with implications for early detection, diagnosis, and therapy of all HPV-driven cancers.Significance:We identify HPV42 as a uniform driver of DPA and add a new member to the short list of tumorigenic viruses in humans. We discover that all oncogenic HPVs evoke a germ cell–like transcriptional program with important implications for detecting, diagnosing, and treating all HPV-driven cancers.See related commentary by Starrett et al., p. 17.This article is highlighted in the In This Issue feature, p. 1

A 64-year-old man with a known history of psoriasis was under regular clinical and reflectance confocal microscopy follow-up for a biopsy-proven lentigo maligna on his right forehead. Five years after the initial diagnosis the lesion gradually disappeared with no concurrent effective treatment. Spontaneous resolution is reported in various skin tumours but to our knowledge, this phenomenon has not been previously described in lentigo maligna.

The classification of vascular lesions is complex. There is a slight overlap between reactive, developmental and benign vascular tumours, and some conditions defy precise classification. This review follows the most recent World Health Organization (WHO) classification of cutaneous vascular tumors and provides the framework for a systematic study, incorporating as many recent advances in molecular and immunohistochemical diagnostics as possible at this moment in time.

The recent WHO classification of skin tumors has underscored the importance of acknowledging intermediate grade melanocytic proliferations. A multistep acquisition of oncogenic events drives the progressive transformation of nevi into melanomas. The various pathways described are modulated by the initial oncogenic drivers that define the common, blue, and Spitz nevi groups. Intermediate lesions are most often the result of a clonal evolution within such nevi. Based on this established classification, we have suggested for each pathway a practical diagnostic approach, benefiting from the recently developed molecular tools, both in the setting of general pathology labs and expert centers. Moreover, recommendations regarding the re-excision and clinical follow-up are given to support decision-making in multidisciplinary tumor boards.

Lymphoepithelioma-like carcinoma of the skin is an extremely rare tumour whose aetiology is yet to be established. An 83-year-old female presented with a rapidly growing plaque on the chest wall diagnosed as lymphoepithelioma-like carcinoma histologically.

In the UK, sea urchin-related injuries (SUIs) most commonly present in returning travellers. Delayed complications mainly affect the skin but nerves, tendons, joints and bones may also be involved. The management of chronic reactions may be challenging and a variety of approaches have been described. Surgical measures are often undertaken, particularly when retained spines are suspected. We demonstrate, through three cases presenting in the UK with chronic SUIs, that conservative management, surgery and intralesional corticosteroids may all be associated with satisfactory outcomes. Management options should consider the presence of retained spines, injury site, symptoms and importantly, patient preference.

Encorafenib is a BRAF inhibitor increasingly used as a second-line treatment for metastatic melanoma and colorectal cancer. BRAF inhibitors have been reported to be associated with new and changing melanocytic lesions, including eruptive naevi. We describe two cases of eruptive naevi secondary to encorafenib used for the treatment of BRAF-mutant metastatic colorectal cancer.

The skin is exposed to viral pathogens, but whether they contribute to the oncogenesis of skin cancers has not been systematically explored. Here we investigated 19 skin tumor types by analyzing off-target reads from commonly available next-generation sequencing data for viral pathogens. We identified human papillomavirus 42 (HPV42) in 96% (n = 45/47) of digital papillary adenocarcinoma (DPA), an aggressive cancer occurring on the fingers and toes. We show that HPV42, so far considered a nononcogenic, “low-risk” HPV, recapitulates the molecular hallmarks of oncogenic, “high-risk” HPVs. Using machine learning, we find that HPV-driven transformation elicits a germ cell–like transcriptional program conserved throughout all HPV-driven cancers (DPA, cervical carcinoma, and head and neck cancer). We further show that this germ cell–like transcriptional program, even when reduced to the top two genes (CDKN2A and SYCP2), serves as a fingerprint of oncogenic HPVs with implications for early detection, diagnosis, and therapy of all HPV-driven cancers. Significance: We identify HPV42 as a uniform driver of DPA and add a new member to the short list of tumorigenic viruses in humans. We discover that all oncogenic HPVs evoke a germ cell–like transcriptional program with important implications for detecting, diagnosing, and treating all HPV-driven cancers. See related commentary by Starrett et al., p. 17. This article is highlighted in the In This Issue feature, p. 1

A 57-year-old man, being managed with a watchful waiting strategy for Stage A chronic lymphocytic leukaemia (CLL), presented, eight years following diagnosis, with itchy spots involving the face, trunk and limbs (Figure 1a). Individual lesions came spontaneously and resolved completely over several weeks. Clinically, there were crops of 4 to 10 mm pruritic, acneiform papules that were not folliculocentric, some of which had a central area of erosion(Figure 1b). Despite trials of lymecycline, topical clindamycin and fucibet therapy, the striking skin eruption progressed in severity becoming widespread and complicated by recurrent secondary Staphylococcal abscesses and an episode of facial erysipelas.

Pure intravascular growth of epithelioid hemangioma (EH) is exceptional. Herein, we report a series of 21 intravascular EHs, representing a potential serious diagnostic pitfall by mimicking malignant vascular neoplsms with epithelioid morphology. The tumors developed in 12 males and 4 females, aged from 11 to 71 years (mean age 40.2 years) with a predilection for the extremities (13 of 21, 61.9%), followed by the head and neck (8 of 21, 38.1%). Lesions ranged in size from 2 to 30 mm (mean size 13 mm). The most common presenting feature was a slowly growing nodule. Most neoplasms were solitary (13 of 16 patients, 81.2%) but three patients developed more than one intravascular EH (3 of 16, 18.8%). Treatment consisted of complete surgical excision and was generally curative. Follow-up was available for 13 lesions that had developed in ten patients (range 4-72 months, mean 27.3 months). No recurrences or development of additional tumors were observed. All 21 lesions developed in subcutaneous veins. Two morphological patterns of intravascular epithelioid endothelial cell proliferation were observed: (1) a lobular capillary hemangioma-like proliferation with variable formation of open vascular lumina and (2) a solid proliferation generally lacking open vascular spaces. A lobular capillary hemangioma-like pattern was the sole pattern in nine lesions, a mixed lobular hemangioma-like pattern, and solid pattern in eight and a pure solid pattern in four intravascular EHs. Mitotic activity in epithelioid endothelial cells ranged from 0 to 7 mitoses per 10 high-power field (mean 2.1 mitoses per 10 HPFs). Six lesions displayed brisk mitotic activity of five or more mitoses per 10 HPF (6 of 21, 28.5%). The number of mitoses was usually more prominent in areas with solid growth. Atypical mitoses were not observed. No intratumoral necroses were seen. Cytological atypia was mild (20 out of 21 cases). By immunohistochemistry, all tumors were positive for CD31 (14 out of 14) and ERG (5 out of 5). While all tested cases were FOS negative by immunohistochemistry (6 out of 6), one out of six cases (case 6) displayed FOSB nuclear positivity in about 30% of the lesional endothelial cells. Eight cases were analysed by FISH for the presence of FOS and FOSB gene rearrangements. While all cases were negative for FOSB rearrangements, a single case proved positive for FOS gene break-apart. In conclusion, intravascular growth of EH is not associated with adverse biological behavior. Solid intravascular proliferations of endothelial cells can mimic a malignant vascular tumor with epithelioid morphology. Nevertheless, intravascular EHs display mild cytological atypia coupled with low mitotic activity, and a lack of atypical mitoses, pronounced nuclear atypia, multilayering or tumor necrosis. Finally, the FOS gene is infrequently rearranged, and there are no FOSB gene abnormalities in this subset of EHs, suggesting a potential distinct pathogenesis than most classic EHs.

The distinction between nevoid melanoma and a mitotically active nevus can be challenging at the microscopic level. In this study, we performed cytogenetic testing on a cohort of 25 mitotically active melanocytic proliferations resembling common melanocytic nevus from 25 patients. Based on cytogenetic findings, the lesions were classified as "nevoid melanoma" (n = 13) or "mitotically active nevus" (n = 12). Subsequently, we compared the clinicopathological features between these 2 groups. Nevoid melanomas occurred in older patients (P = 0.007); however, there were no significant differences in gender, size, or anatomical distribution between the 2 groups. Histologically, deep/marginal mitoses (P = 0.006), lack of maturation with depth (P = 0.036), and pseudo-maturation (P = 0.006) were significantly more common in nevoid melanomas. Immunohistochemically, complete loss of p16 was an important divisive feature (P = 0.0004), seen in 70% of nevoid melanomas, and highly correlated with loss of CDKN2A gene (chromosome 9p21). Our findings suggest that such reproducible immunomorphological differences can be of value in distinguishing nevoid melanoma from mitotically active nevus. Nevoid melanomas demonstrated a spectrum of chromosomal aberrations similar to those seen in common subtypes of melanoma, which can serve as a powerful adjunct diagnostic tool in morphologically challenging lesions.

Tumours derived from/differentiating towards the hair follicle are relatively rare and the nomenclature is somewhat confusing. A seemingly difficult task of classifying and stratifying various follicular tumours can be made easier by grouping various follicular tumours according to lines of differentiation pertaining to the specific anatomical compartments within the hair follicle. This review paper aims to improve the understanding of follicular tumours and provide several key points in order to facilitate their diagnosis.

Epidermolysis bullosa acquisita is a highly uncommon condition in the paediatric population. This article describes three children with this disease, different clinical presentation and management. It also reviews the most relevant articles on this topic.

Linked Article: Cook et al. Br J Dermatol 2022; 186:167–173.

The differential diagnosis of atypical dermal nonepidermotropic CD8To assess the clinical, histological and immunophenotypic features; outcomes of; and differences between dermal CD8Retrospective analysis of a series of 46 patients and biopsies by the international EORTC Cutaneous Lymphoma Group.The dermal CD8A constellation of distinct clinical, histopathological and phenotypic features allows discrimination and assignment of dermal CD8

Background and Aims Metastatic Crohn’s disease is an extraintestinal cutaneous manifestation characterised by non-specific inflammatory lesions anatomically separate from the gut; genital involvement is rare. We conducted a systematic review of anogenital Crohn’s disease and granulomatosis, to provide a synthesis of epidemiology, clinical features, and treatment outcomes. Methods A systematic search of the literature was conducted via MEDLINE, EMBASE, and the Cochrane database from inception to December 1, 2020. Two investigators extracted and analysed study data. Response and remission were defined as partial improvement or complete resolution of symptoms and examination findings, respectively. Results Of 9381 screened studies, 185 articles, [410 cases: 273 female, 137 male] were included. The predominant clinical features were oedema, ulcers, fissures, and hypertrophic lesions. Adults and children present similarly. Luminal Crohn’s disease was diagnosed in nearly 80% of cases including 45–80% patients without gastrointestinal symptoms (time to inflammatory bowel disease [IBD] from anogenital Crohn’s disease diagnosis [range] –43 to 11 years). Antibiotics, corticosteroids, thiopurines, and anti-tumour necrosis factor [TNF] therapy were the most frequently prescribed agents. At final follow-up, non-response, response, and remission rates were 37/304 [12%], 267/304 [88%], and 114/304 [38%], respectively. Oedema was associated with a poor response to topical therapy. Greater response rates to anti-TNF therapy were seen in patients prescribed concomitant immunomodulation [24/25, 96% vs 67/90, 74%, p = 0.02]. Conclusions We provide an illustrative summary of the clinical presentation and treatment effectiveness of this rare, under-recognised condition, and a proposed algorithm for approach and management. Prospective studies with longer follow-up are required to define optimal treatment strategies.

Amelanotic/hypomelanotic variant of cellular blue naevus (CBN) can present a challenge for the clinician and histopathologist. We report a case of amelanotic/hypomelanotic variant of CBN that presented as a painless scrotal swelling in a child. We review the literature on amelanotic/hypomelanotic CBN, the key histological features and important differential diagnoses.

Summary Glomus tumours (GTs) have traditionally been classified into benign GTs, GTs with uncertain malignant potential and malignant GTs, based on a combination of criteria such as size of the tumour, degree of nuclear atypia and the level of mitotic activity. Several of the proposed grading criteria are difficult, or even impossible to apply for GTs occurring in the skin. The aim of the study was to analyse the applicability of the currently established GT malignancy criteria for tumours occurring in the skin and to establish their prognostic significance. A total of 25 benign cutaneous GTs, 11 new cutaneous malignant GTs and 36 cutaneous malignant GTs previously published in the literature were studied. We analysed the following clinicopathological features and correlated them with disease outcome: age, sex, site, size, depth of invasion, degree of nuclear atypia, mitotic activity, growth pattern, vascular invasion, spindle-cell morphology and tumoural necrosis. Of all the clinicopathological parameters analysed, only tumoural necrosis was found by univariate analysis (p = 0.001) to be associated with adverse biological behaviour, and none by multivariate analysis. Multivariate statistical analysis failed to detect any clinicopathological features predictive of the disease outcome (e.g., local recurrence, development of metastatic spread and/or death of disease) in cutaneous malignant GTs. Furthermore, the currently established malignancy criteria for cutaneous GTs can be difficult to apply, mainly due to their smaller size. Likewise, counting mitotic activity per 50 high power fields can often not be accomplished in GTs occurring at superficial locations. Complete excision of these tumours coupled with long-term follow-up is the mainstay of treatment for cutaneous malignant GTs. The results of our study also suggest that cutaneous malignant GTs follow a more indolent clinical course than their deep soft tissue counterparts.

Dermal hyperneury (DN) is a rarely reported form of small nerve hypertrophy characterized by an exaggerated size and prominence of dermal nerve fibers. Clinically, it can present with or without visible lesions, within a syndrome or sporadically, and in solitary or multiple fashion. The syndromes most commonly associated with DN include multiple endocrine neoplasia 2B and 2A, neurofibromatosis type II, and Cowden syndrome. Patients with syndrome-associated DN have an increased risk for various malignancies. Sporadic DN has been reported either in association with cutaneous tumors/reactive lesions, such as nodular prurigo, or in idiopathic form, where it can present with multiple DN lesions. There is a morphologic overlap between mucocutaneous neuromas and DN, as the former can have the appearance of either bulkier circumscribed lesions or tortuous and hyperplastic nerves more akin to DN. Epithelial sheath neuroma also shares a similar appearance to DN, from which it can be distinguished by a squamoid-appearing and thickened perineurium.

International audience; While virus-negative Merkel cell carcinoma (MCC) is characterized by high frequency of UV-induced mutations, expression of two viral oncoproteins is regarded as key mechanism driving Merkel cell polyomavirus (MCPyV)-positive MCC. The cells in which these molecular events initiate MCC oncogenesis have yet not been identified for both MCC subsets. A considerable proportion of virus-negative MCC is found in association with squamous cell carcinoma (SCC) suggesting (i) coincidental collision, (ii) one providing a niche for the other or (iii) one evolving from the other. Whole exome sequencing of four combined tumors consisting of SCC in situ and MCPyV-negative MCC demonstrated in all cases many mutations shared between SCC and MCC indicating a common ancestry and thereby a keratinocytic origin of these MCCs. Moreover, analyses of the combined cases as well as of pure SCC and MCC suggests that RB1 inactivation in SCC facilitates MCC development and that epigenetic changes may contribute to the SCC/MCC transition.

The recent WHO classification of skin tumors has underscored the importance of acknowledging intermediate grade melanocytic proliferations. A multistep acquisition of oncogenic events drives the progressive transformation of nevi into melanomas. The various pathways described are modulated by the initial oncogenic drivers that define the common, blue, and Spitz nevi groups. Intermediate lesions are most often the result of a clonal evolution within such nevi. Based on this established classification, we have suggested for each pathway a practical diagnostic approach, benefiting from the recently developed molecular tools, both in the setting of general pathology labs and expert centers. Moreover, recommendations regarding the re-excision and clinical follow-up are given to support decision-making in multidisciplinary tumor boards.

Aims Microcystic adnexal carcinoma is a distinctive sweat duct carcinoma of low-grade malignant potential with a risk for locally destructive growth and local recurrence. Distant metastases and disease-related mortality are exceptional. The histological hallmarks of these tumours are the diffusely infiltrative growth within the dermis, the frequent invasion of subcutaneous structures, the presence of perineurial invasion, and the bland cytological features. The tumours are organised in cords and strands, and show keratocyst formation and duct differentiation in varying proportions. Marked cytological atypia, nuclear pleomorphism, brisk and atypical mitotic activity and necrosis are not typically seen in these tumours. Methods and results We report two patients presenting with large, slowly growing tumours on the face showing areas of morphologically high-grade carcinoma arising on a background of unequivocal microcystic adnexal carcinoma. Both patients are alive with follow-up of up to 6 years, with no evidence of disease. Conclusions Morphologically high-grade transformation in microcytic adnexal carcinoma is a rare phenomenon that does not appear to confer a risk for aggressive behaviour. Recognition depends on sampling of the areas of conventional microcystic adnexal carcinoma.

Dermatofibromas are common benign skin lesions, the etiology of which is poorly understood. We identified two unrelated pedigrees in which there was autosomal dominant transmission of multiple dermatofibromas. Whole exome sequencing revealed a rare shared heterozygous missense variant in the F13A1 gene encoding factor XIII subunit A (FXIII-A), a transglutaminase involved in hemostasis, wound healing, tumor growth, and apoptosis. The variant (p.Lys679Met) has an allele frequency of 0.0002 and is predicted to be a damaging mutation. Recombinant human Lys679Met FXIII-A demonstrated reduced fibrin crosslinking activity in vitro. Of note, the treatment of fibroblasts with media containing Lys679Met FXIII-A led to enhanced adhesion, proliferation, and type I collagen synthesis. Immunostaining revealed co-localization between FXIII-A and α4β1 integrins, more prominently for Lys679Met FXIII-A than the wild type. In addition, both the α4β1 inhibitors and the mutation of the FXIII-A Isoleucine-Leucine-Aspartate-Threonine (ILDT) motif prevented Lys679Met FXIII-A-dependent proliferation and collagen synthesis of fibroblasts. Our data suggest that the Lys679Met mutation may lead to a conformational change in the FXIII-A protein that enhances α4-integrin binding and provides insight into an unexpected role for FXIII-A in the pathobiology of familial dermatofibroma.