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Background Chilblains ('COVID toes') are being seen with increasing frequency in children and young adults during the COVID-19 pandemic. Detailed histopathological descriptions of COVID-19 chilblains have not been reported, and causality of SARS-CoV-2 has not yet been established. Objectives To describe the histopathological features of COVID-19 chilblains and to explore the presence of SARS-CoV-2 in the tissue. Methods We examined skin biopsies from seven paediatric patients presenting with chilblains during the COVID-19 pandemic. Immunohistochemistry for SARS-CoV-2 was performed in all cases and electron microscopy in one. Results Histopathology showed variable degrees of lymphocytic vasculitis ranging from endothelial swelling and endotheliitis to fibrinoid necrosis and thrombosis. Purpura, superficial and deep perivascular lymphocytic inflammation with perieccrine accentuation, oedema, and mild vacuolar interface damage were also seen. SARS-CoV-2 immunohistochemistry was positive in endothelial cells and epithelial cells of eccrine glands. Coronavirus particles were found in the cytoplasm of endothelial cells on electron microscopy. Conclusions Although the clinical and histopathological features were similar to other forms of chilblains, the presence of viral particles in the endothelium and the histological evidence of vascular damage support a causal relation of the lesions with SARS-CoV-2. Endothelial damage induced by the virus could be the key mechanism in the pathogenesis of COVID-19 chilblains and perhaps also in a group of patients severely affected by COVID-19 presenting with features of microangiopathic damage. What is already known about this topic? Despite the high number of cases of chilblains seen during the COVID-19 pandemic, a definite causative role for SARS-CoV-2 has not yet been proven. Different pathogenetic hypotheses have been proposed, including coagulation anomalies, interferon release and external factors. What does this study add? The demonstration of SARS-CoV-2 in endothelial cells of skin biopsies by immunohistochemistry and electron microscopy confirms that these lesions are part of the spectrum of COVID-19. Virus-induced vascular damage and secondary ischaemia could explain the pathophysiology of COVID-19 chilblains. Our findings support the hypothesis that widespread endothelial infection by SARS-CoV-2 could have a pathogenetic role in the severe forms of COVID-19. Linked Comment: Wetter. Br J Dermatol 2020; 183:611.

Blue nevi are melanocytic tumors originating in the cutaneous dermis. Malignant tumors may arise in association with or resembling blue nevi, so called ‘blue nevus-like melanoma’, which can metastasize and result in patient death. Identifying which tumors will behave in a clinically aggressive manner can be challenging. Identifying genetic alterations in such tumors may assist in their diagnosis and prognostication. Blue nevi are known to be genetically related to uveal melanomas (eg, both harboring GNAQ and GNA11 mutations). In this study, we analyzed a large cohort (n=301) of various morphologic variants of blue nevi and related tumors including tumors diagnosed as atypical blue nevi (n=21), and blue nevus-like melanoma (n=12), screening for all gene mutations known to occur in uveal melanoma. Similar to published reports, we found the majority of blue nevi harbored activating mutations in GNAQ (53%) or GNA11 (15%). In addition, rare CYSLTR2 (1%) and PLCB4 (1%) mutations were identified. EIF1AX, SF3B1, and BAP1 mutations were also detected, with BAP1 and SF3B1 R625 mutations being present only in clearly malignant tumors (17% (n=2) and 25% (n =3) of blue nevus-like melanoma, respectively). In sequencing data from a larger cohort of cutaneous melanomas, this genetic profile was also identified in tumors not originally diagnosed as blue nevus-like melanoma. Our findings suggest that the genetic profile of coexistent GNAQ or GNA11 mutations with BAP1 or SF3B1 mutations can aid the histopathological diagnosis of blue nevus-like melanoma and distinguish blue nevus-like melanoma from conventional epidermal-derived melanomas. Future studies will need to further elucidate the prognostic implications and appropriate clinical management for patients with tumors harboring these mutation profiles.

Merkel cell carcinoma is a primary cutaneous neuroendocrine carcinoma, which once metastatic is difficult to treat. Recent mutation analyses of Merkel cell carcinoma revealed a low number of mutations in Merkel cell polyomavirus-associated tumors, and a high number of mutations in virus-negative combined squamous cell and neuroendocrine carcinomas of chronically sun-damaged skin. We speculated that the paucity of mutations in virus-positive Merkel cell carcinoma may reflect a pathomechanism that depends on derangements of chromatin without alterations in the DNA sequence (epigenetic dysregulation). One central epigenetic regulator is the Polycomb repressive complex 2 (PRC2), which silences genomic regions by trimethylating (me3) lysine (K) 27 of histone H3, and thereby establishes the histone mark H3K27me3. Recent experimental research data demonstrated that PRC2 loss in mice skin results in the formation of Merkel cells. Prompted by these findings, we explored a possible contribution of PRC2 loss in human Merkel cell carcinoma. We examined the immunohistochemical expression of H3K27me3 in 35 Merkel cell carcinomas with pure histological features (22 primary and 13 metastatic lesions) and in 5 combined squamous and neuroendocrine carcinomas of the skin. We found a strong reduction of H3K27me3 staining in tumors with pure histologic features and virus-positive Merkel cell carcinomas. Combined neuroendocrine carcinomas had no or only minimal loss of H3K27me3 labeling. Our findings suggest that a PRC2-mediated epigenetic deregulation may play a role in the pathogenesis of virus-positive Merkel cell carcinomas and in tumors with pure histologic features.

Histopathological evaluation of melanocytic tumours usually allows reliable distinction of benign melanocytic naevi from melanoma. More difficult is the histopathological classification of Spitz tumours, a heterogeneous group of tumours composed of large epithelioid or spindle-shaped melanocytes. Spitz tumours are biologically distinct from conventional melanocytic naevi and melanoma, as exemplified by their distinct patterns of genetic aberrations. Whereas common acquired naevi and melanoma often harbour BRAF mutations, NRAS mutations, or inactivation of NF1, Spitz tumours show HRAS mutations, inactivation of BAP1 (often combined with BRAF mutations), or genomic rearrangements involving the kinases ALK, ROS1, NTRK1, BRAF, RET, and MET. In Spitz naevi, which lack significant histological atypia, all of these mitogenic driver aberrations trigger rapid cell proliferation, but after an initial growth phase, various tumour suppressive mechanisms stably block further growth. In some tumours, additional genomic aberrations may abrogate various tumour suppressive mechanisms, such as cell-cycle arrest, telomere shortening, or DNA damage response. The melanocytes then start to grow in a less organised fashion and may spread to regional lymph nodes, and are termed atypical Spitz tumours. Upon acquisition of even more aberrations, which often activate additional oncogenic pathways or alter cell differentiation, the neoplastic cells become entirely malignant and may colonise and take over distant organs (spitzoid melanoma). The sequential acquisition of genomic aberrations suggests that Spitz tumours represent a continuous biological spectrum, rather than a dichotomy of benign versus malignant, and that tumours with ambiguous histological features (atypical Spitz tumours) might be best classified as low-grade melanocytic tumours. The number of genetic aberrations usually correlates with the degree of histological atypia and explains why existing ancillary genetic techniques, such as array comparative genomic hybridisation (CGH) or fluorescence in situ hybridisation (FISH), are usually capable of accurately classifying histologically benign and malignant Spitz tumours, but are not very helpful in the diagnosis of ambiguous melanocytic lesions. Nevertheless, we expect that progress in our understanding of tumour progression will refine the classification of spitzoid melanocytic tumours in the near future. By integrating clinical, pathological, and genetic criteria, distinct tumour subsets will be defined within the heterogeneous group of Spitz tumours, which will eventually lead to improvements in diagnosis, prognosis and therapy.

Purpose: The aim of this study was to use massively parallel DNA sequencing to identify GNAQ/11, BAP1 and SF3B1 mutations in ophthalmic melanocytoma. Procedures: Six ophthalmic melanocytoma specimens (1 iridociliary and 5 optic nerve) were profiled for genomic alterations in GNAQ/11, BAP1 and SF3B1 using a custom deep sequencing assay. This assay uses solution phase hybridization-based exon capture and deep-coverage massively parallel DNA sequencing to interrogate all protein-coding exons and select introns. Results: The only iridociliary melanocytoma showed a mutation in GNAQ but not in BAP1. Of the 2 optic-nerve melanocytomas that developed into melanoma, one had a GNAQ mutation and both a BAP1 mutation and monosomy 3. The remaining 3 optic-nerve melanocytomas did not reveal mutations in GNAQ/11 or BAP1. SF3B1 mutations were not detected in any specimen. Conclusions: The presence of GNAQ mutation in some iridociliary and optic-nerve melanocytomas suggests a possible relationship between ophthalmic melanocytoma and other ophthalmic melanocytic neoplasms. BAP1 mutation may accompany the transformation of ophthalmic melanocytoma to melanoma.

Atypical fibroxanthomas and pleomorphic dermal sarcomas are tumors arising in sun-damaged skin of elderly patients. They have differing prognoses and are currently distinguished using histological criteria, such as invasion of deeper tissue structures, necrosis and lymphovascular or perineural invasion. To investigate the as-yet poorly understood genetics of these tumors, 41 atypical fibroxanthomas and 40 pleomorphic dermal sarcomas were subjected to targeted next-generation sequencing approaches as well as DNA copy number analysis by comparative genomic hybridization. In an analysis of the entire coding region of 341 oncogenes and tumor suppressor genes in 13 atypical fibroxanthomas using an established hybridization-based next-generation sequencing approach, we found that these tumors harbor a large number of mutations. Gene alterations were identified in more than half of the analyzed samples in FAT1, NOTCH1/2, CDKN2A, TP53, and the TERT promoter. The presence of these alterations was verified in 26 atypical fibroxanthoma and 35 pleomorphic dermal sarcoma samples by targeted amplicon-based next-generation sequencing. Similar mutation profiles in FAT1, NOTCH1/2, CDKN2A, TP53, and the TERT promoter were identified in both atypical fibroxanthoma and pleomorphic dermal sarcoma. Activating RAS mutations (G12 and G13) identified in 3 pleomorphic dermal sarcoma were not found in atypical fibroxanthoma. Comprehensive DNA copy number analysis demonstrated a wide array of different copy number gains and losses, with similar profiles in atypical fibroxanthoma and pleomorphic dermal sarcoma. In summary, atypical fibroxanthoma and pleomorphic dermal sarcoma are highly mutated tumors with recurrent mutations in FAT1, NOTCH1/2, CDKN2A, TP53, and the TERT promoter, and a range of DNA copy number alterations. These findings suggest that atypical fibroxanthomas and pleomorphic dermal sarcomas are genetically related, potentially representing two ends of a common tumor spectrum and distinguishing these entities is at present still best performed using histological criteria.Modern Pathology advance online publication, 3 November 2017; doi:10.1038/modpathol.2017.146.

Hintergrund Spitzoide melanozytare Neoplasien (Spitz-Navi, atypische Spitz-Tumoren, spitzoide Melanome) sind eine klinisch, histopathologisch und genetisch heterogene Gruppe melanozytarer Hauttumoren.

Blue nevi are common melanocytic tumors arising in the dermal layer of the skin. Similar to uveal melanomas, blue nevi frequently harbor GNAQ and GNA11 mutations. Recently, recurrent CYSLTR2 and PLCB4 mutations were identified in uveal melanomas not harboring GNAQ or GNA11 mutations. All four genes (GNAQ, GNA11, CYSLTR2, and PLCB4) code for proteins involved in the same signaling pathway, which is activated by mutations in these genes. Given the related functional consequences of these mutations and the known genetic similarities between uveal melanoma and blue nevi, we analyzed a cohort of blue nevi to investigate whether CYSLTR2 and PLCB4 mutations occur in tumors lacking GNAQ or GNA11 mutations (as in uveal melanoma). A targeted next-generation sequencing assay covering known activating mutations in GNAQ, GNA11, CYSLTR2, PLCB4, KIT, NRAS, and BRAF was applied to 103 blue nevi. As previously reported, most blue nevi were found to harbor activating mutations in GNAQ (59%, n = 61), followed by less frequent mutations in GNA11 (16%, n = 17). Additionally, one BRAF (1%) and three NRAS (3%) mutations were detected. In three tumors (3%) harboring none of the aforementioned gene alterations, CYSLTR2 mutations were identified. All three CYSLTR2 mutations were the same c.386T > A, L129Q mutation previously identified in uveal melanoma that has been shown to lead to increased receptor activation and signaling. In summary, our study identifies CYSLTR2 L129Q alterations as a previously unrecognized activating mutation in blue nevi, occuring in a mutually exclusive fashion with known GNAQ and GNA11 mutations. Similar to GNAQ and GNA11 mutations, CYSLTR2 mutations, when present, are likely defining pathogenetic events in blue nevi.

Most malignant peripheral nerve sheath tumors (MPNSTs) exhibit combined inactivation of NF1, CDKN2A, and polycomb repressive complex 2 component genes (Embryonic Ectoderm Development [EED] and Suppressor of Zeste 12 [SUZ12]). Mutations in EED and SUZ12 induce loss of trimethylation at lysine 27 of histone 3 (H3K27me3), with subsequent aberrant transcriptional activation of polycomb repressive complex 2–repressed homeobox master regulators. These findings prompted us to investigate the performance of an anti-H3K27me3 monoclonal antibody clone C36B11 as an immunohistochemical marker for MPNSTs. We assessed the C36B11 reactivity pattern in a pathologically and genetically well-characterized cohort of 68 MPNSTs, spanning various clinical presentations, such as type 1 neurofibromatosis (NF1), radiotherapy, and sporadic MPNSTs. We found that 69% (n=47) of all MPNSTs demonstrated loss of H3K27me3 expression, with 42 (61%) showing complete loss and 5 (7%) showing partial loss, whereas 31% (n = 21) retained H3K27me3 expression. Among the NF1-related high-grade MPNSTs, 60% demonstrated loss of expression. In contrast, the majority of both sporadic (95%) and radiotherapy-related (91%) MPNSTs showed loss of H3K27me3 expression. Two of the 3 low-grade MPNSTs and all neurofibromas showed retained expression. Furthermore, all 5 epithelioid MPNSTs retained H3K27me3 labeling. The specificity of H3K27me3 loss as a marker for MPNSTs was studied by testing a large spectrum of lesions included in MPNST differential diagnosis, such as spindle/desmoplastic melanomas, synovial sarcomas, myoepithelial tumors, and other mesenchymal neoplasms, all of which retained expression of H3K27me3. We conclude that immunohistochemical analysis of H3K27me3 has good sensitivity and robust specificity for the diagnosis of MPNST, particularly outside of NF1 clinical history, which represents the most challenging diagnostic setting.

Spitz tumors are a group of melanocytic neoplasms with distinct morphological features that tend to affect young individuals. Distinguishing benign from malignant Spitz tumors can be challenging, but cytogenetic and molecular tests have contributed to improvements in diagnostic accuracy. Spitz tumors harbor diverse genetic alterations, including mutations in HRAS, loss of BAP1, or kinase fusions in ROS1, NTRK1, ALK, BRAF, and RET genes. Limited data exist on the correlation between histopathological features and kinase fusions. Here, we describe the histopathological features of 105 Spitz tumors (Spitz nevi and atypical Spitz tumors), comparing lesions according to their immunoreactivity for ALK or NTRK1. Intersecting fascicular growth of fusiform melanocytes was seen in all but one ALK-positive tumor (27 of 28 or 96.4%), whereas it was infrequent in NTRK1-positive tumors (5 of 20 or 25.0%) and tumors negative for both ALK and NTRK1 (96.4% vs 25.0% vs 8.7%, P < .0027). There was a trend toward ALK-positive tumors being amelanotic compared with NTRK1-positive tumors and combined ALK-/NTRK1-negative tumors (89.3% vs 45% vs 47.4%, respectively, P = .1023) and lacking epithelioid cell morphology (0% vs 45.0% vs 41%, respectively, P = .6985). In conclusion, this study confirms that although not specific, the growth pattern of intersecting fascicles of amelanotic fusiform melanocytes is strongly associated with ALK expression.

We recently reported that germline mutations in BAP1 cause a familial tumor syndrome characterized by high penetrance for melanocytic tumors with distinct clinical and histologic features. Melanocytic neoplasms in affected individuals harbored BRAF mutations, showed loss of BAP1 expression, and histologically resembled so-called "atypical Spitz tumors" (ASTs). ASTs are an ill-defined and probably heterogenous group of melanocytic tumors that display histologic features seen in both Spitz nevi and melanomas. Their biological behavior cannot be reliably predicted. In view of the histologic similarities of the familial tumors and ASTs, we hypothesized that a subset of ASTs might harbor genetic alterations seen in the familial tumors. To address this hypothesis, we analyzed 32 sporadic ASTs for BRAF mutations and for BAP1 expression. Nine (28%) sporadic ASTs showed loss of BAP1 expression, of which 8 (89%) had concomitant BRAF mutations. Only 1 of the BAP1-positive ASTs (4%) had a BRAF mutation (P

Cutaneous melanomas are characterized by a range of histological appearances, and several morphological variants have been described. In this study, we report a variant of superficial spreading melanoma that is characterized by large, irregular junctional melanocytic nests. The junctional nests varied in shape and size, showed focal tendency to confluence, and were often surrounded by a cuff of epidermal keratinocytes. The melanocytes comprising the nests showed variable cytological atypia. In most of the cases, scant intraepidermal or junctional single melanocytes were seen, and other well-documented diagnostic criteria for melanoma were lacking, and as a result, histological recognition of these tumors as melanoma was difficult. Some cases were associated with an invasive dermal component or showed evidence of sun damage. To provide supporting evidence for malignancy, we analyzed these tumors for genomic aberrations. Using array comparative genomic hybridization (aCGH), we identified multiple genomic aberrations in all analyzed cases. A similar pattern of genomic aberrations was seen in a control group of bona fide superficial spreading melanomas, suggesting that these 'melanomas composed exclusively or predominantly of large nests' are indeed variants of superficial spreading melanoma. Fluorescence in-situ hybridization (FISH) was positive in 40% of the cases. However, using aCGH, the FISH-negative cases showed multiple genomic aberrations in regions that are not covered by FISH. The low sensitivity of the FISH test can be explained by the fact that FISH only evaluates four genomic loci for aberrations, whereas aCGH surveys the entire genome. In summary, we present histological and molecular genetic evidence for a morphological variant of superficial spreading melanoma. Awareness of the histological features will aid in their correct diagnosis as melanoma, and in difficult cases, judicious application of ancillary tests such as aCGH (rather than FISH) will assist accurate diagnosis.

Common acquired melanocytic nevi are benign neoplasms that are composed of small, uniform melanocytes and are typically present as flat or slightly elevated pigmented lesions on the skin. We describe two families with a new autosomal dominant syndrome characterized by multiple, skin-colored, elevated melanocytic tumors. In contrast to common acquired nevi, the melanocytic neoplasms in affected family members ranged histopathologically from epithelioid nevi to atypical melanocytic proliferations that showed overlapping features with melanoma. Some affected individuals developed uveal or cutaneous melanomas. Segregating with this phenotype, we found inactivating germline mutations of BAP1, which encodes a ubiquitin carboxy-terminal hydrolase. The majority of melanocytic neoplasms lost the remaining wild-type allele of BAP1 by various somatic alterations. In addition, we found BAP1 mutations in a subset of sporadic melanocytic neoplasms showing histological similarities to the familial tumors. These findings suggest that loss of BAP1 is associated with a clinically and morphologically distinct type of melanocytic neoplasm.

Recently, initial studies describing the use of multicolor fluorescence in situ hybridization (FISH) for classifying melanocytic skin lesions have been published demonstrating a high sensitivity and specificity in discriminating melanomas from nevi. However, the majority of these studies included neither histologically ambiguous lesions nor a clinical long-term follow up. This study was undertaken to validate a special multicolor FISH test in histologically ambiguous melanocytic skin lesions with known clinical long-term follow up. FISH was scored by three independent pathologists in a series of 22 melanocytic skin lesions, including 12 ambiguous cases using four probes targeting chromosome 6p25, centromere 6, 6q23, and 11q13. The FISH results were compared with array comparative genomic hybridization data and correlated to the clinical long-term follow up (mean: 65 months). Pair-wise comparison between the interpretations of the observers showed a moderate to substantial agreement (kappa 0.47-0.61). Comparing the FISH results with the clinical behavior reached an overall sensitivity of 60% and a specificity of 50% (chi(2)=0.25; P=0.61) for later development of metastases. Comparison of array comparative genomic hybridization data with FISH analyses did not yield significant results but array comparative genomic hybridization data demonstrated that melanocytic skin lesions with the development of metastases showed significantly more chromosomal aberrations (P

BACKGROUND Uveal melanoma is the most common intraocular cancer. There are no effective therapies for metastatic disease. Mutations in GNAQ, the gene encoding an alpha subunit of heterotrimeric G proteins, are found in 40% of uveal melanomas. METHODS We sequenced exon 5 of GNAQ and GNA11, a paralogue of GNAQ, in 713 melanocytic neoplasms of different types (186 uveal melanomas, 139 blue nevi, 106 other nevi, and 282 other melanomas). We sequenced exon 4 of GNAQ and GNA11 in 453 of these samples and in all coding exons of GNAQ and GNA11 in 97 uveal melanomas and 45 blue nevi. RESULTS We found somatic mutations in exon 5 (affecting Q209) and in exon 4 (affecting R183) in both GNA11 and GNAQ, in a mutually exclusive pattern. Mutations affecting Q209 in GNA11 were present in 7% of blue nevi, 32% of primary uveal melanomas, and 57% of uveal melanoma metastases. In contrast, we observed Q209 mutations in GNAQ in 55% of blue nevi, 45% of uveal melanomas, and 22% of uveal melanoma metastases. Mutations affecting R183 in either GNAQ or GNA11 were less prevalent (2% of blue nevi and 6% of uveal melanomas) than the Q209 mutations. Mutations in GNA11 induced spontaneously metastasizing tumors in a mouse model and activated the mitogen-activated protein kinase pathway. CONCLUSIONS Of the uveal melanomas we analyzed, 83% had somatic mutations in GNAQ or GNA11. Constitutive activation of the pathway involving these two genes appears to be a major contributor to the development of uveal melanoma. (Funded by the National Institutes of Health and others.).

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a neoplasm derived from precursors of plasmacytoid dendritic cells. Cutaneous involvement represents often the first manifestation of the disease. We studied 45 skin biopsies from 33 patients (M:F=7.25:1; median age: 71 y; age range: 30 to 89) with BPDCN to delineate histopathologic and immunophenotypic features of this disease. Patients presented with generalized (n=18), localized (n=6), or solitary (n=9) macules, plaques, and/or tumors. Staging investigations at presentation were negative in 20 patients. Unusual histologic features included a perivascular/periadnexal pattern (6 biopsies from 4 patients) and the presence of pleomorphism of neoplastic cells with blastoid cells admixed with elongated, twisted, or hyperchromatic cells (observed in 24 specimens). Negativity of 1 among the 4 markers CD4, CD56, CD123, and TCL-1 was seen in 11 biopsies, and of 2 markers in 4 biopsies. Staining for CD68 revealed positivity of the majority of cells in 1 and of scattered cells in 24/37 stained cases. Terminal deoxynucleotidyl transferase was observed in 22/37 stained cases. Staining for Bcl-6, MUM-1 and FOX-P1 revealed positivity of a variable proportion of neoplastic cells in 16/30, 19/29, and 21/23 cases, respectively. Our study shows that cutaneous lesions of BPDCN display a greater variability of morphologic and phenotypic features than recognized earlier. Discrete perivascular infiltrates, pleomorphic morphology of neoplastic cells, and unusual phenotypic profiles may be the source of diagnostic pitfalls. These atypical variants should be recognized to make an early diagnosis and to manage properly patients with this aggressive hematological disorder.

Cutaneous lymphomas represent a heterogeneous group of malignant lymphoid diseases with particular tropism for the skin. Prognosis and treatment depend on the type of lymphoma, thus precise diagnosis and classification are of paramount importance. Classification of cutaneous lymphomas relies on a synthesis of all available information, including clinical history and presentation, histopathology, immunophenotype, and molecular data. Thanks to the efforts of the lymphoma groups of both the World Health Organization (WHO) and the European Organization for Research and Treatment of Cancer (EORTC), a joint WHO-EORTC classification for primary cutaneous lymphomas has been proposed in 2005. The WHO-EORTC classification has been adsorbed with minor changes in the 2008 WHO classification of tumours of haematopoietic and lymphoid tissues, thus including for the first time primary cutaneous lymphomas as distinct subtypes of extranodal lymphomas in a general classification of lymphomas.

Desmoplastic melanoma (DM) is a rare variant of melanoma with distinct clinical, histopathologic, and immunohistochemical features. Clinically, DM differs from conventional melanoma by a higher propensity for local recurrence and less frequent metastatic spread to regional lymph nodes. In its pure form, DM has a distinct appearance displaying a low density of fusiform melanocytes in a collagen-rich matrix. While a number of mutations have been identified in primary melanoma, including BRAF, NRAS, GNAQ, GNA11 and KIT, and the occurrence of these mutations has been found to correlate to some extent with the histopathologic features, anatomic site and/or mode of sun exposure, no distinct set of mutations has so far been reported for DM. To study the potential association of neurofibromin (NF1) mutations with DM, we examined 15 desmoplastic and 20 non-desmoplastic melanomas by next-generation sequencing. Mutations of the NF1 gene were found in 14 of 15 (93%) desmoplastic and 4 of 20 (20%) non-desmoplastic melanomas. The high frequency of NF1 mutations in desmoplastic melanomas suggests an important role for NF1 in the biology of this type of melanoma.

Germline loss of function mutations in BAP1 are associated with the development of cutaneous melanocytic tumors with some histopathologic characteristics seen in Spitz nevi. Similar melanocytic tumors occurring in a sporadic setting have been demonstrated to have biallelic loss of BAP1. In some of these sporadic tumors, loss of BAP1 occurs through mutation of one allele and genomic loss of the other. We screened our database of comparative genomic hybridization profiles of ambiguous melanocytic tumors to identify cases with a single genomic event involving loss of the BAP1 locus. The prevalence of tumors with a single genomic event involving loss of BAP1 was 6.7% in our study population. We further characterized the BAP1 status in 17 of these tumors with available additional material, confirming loss of BAP1 in all cases. We describe BAP1 loss in a blue nevus like melanoma and further expand the histopathologic spectrum of spitzoid melanocytic neoplasms with BAP1 loss.

Spitz tumors represent a group of melanocytic neoplasms that typically affects young individuals. Microscopically the lesions are composed of cytologically distinct spindle and epithelioid melanocytes, with a range in the architectural display or the cells, their nuclear features, and secondary epidermal or stromal changes. Recently, kinase fusions have been documented in a subset of Spitz tumors, but there is limited information on the clinical and pathologic features associated with those lesions. Here, we report a series of 17 patients (9 male, 8 female) with spitzoid neoplasms showing ALK fusions (5 Spitz nevi and 12 atypical Spitz tumors). The patients’ ages ranged from 2 years to 35 years (mean = 17; median = 16). Most lesions were located on the lower extremities and presented clinically as polypoid nodules. All tumors were compound melanocytic proliferations with a predominant intradermal growth. Tumor thickness ranged from 1.1 to 6 mm (mean = 2.9 mm; median = 2.5 mm). The most characteristic histopathologic feature of the tumors (seen in all but two lesions) was a plexiform dermal growth of intersecting fascicles of fusiform melanocytes. All but two tumors were amelanotic. All tumors were strongly immunoreactive for ALK. The ALK rearrangements were confirmed in all cases by fluorescence in situ hybridization (FISH) and the fusion partner was determined by quantitative polymerase chain reaction as TPM3 (tropomyosin 3) in 11 cases and DCTN1 (dynactin 1) in 6 cases. None of the eight tumors, which were analyzed by FISH for copy number changes of 6p, 6q, 9p, or 11q met criteria for melanoma. Two patients underwent a sentinel lymph node biopsy, and in both cases melanocytes nests were found in the subcapsular sinus of the node. Array comparative genomic hybridization of these two tumors revealed no chromosomal gains or losses. In conclusion, our study revealed that Spitz nevi/tumors with ALK rearrangement show a characteristic plexiform morphology and that ALK immunohistochemistry and FISH enables the accurate identification of this morphologic and genetic distinct subset of spitzoid neoplasms.

Cutaneous lesions of lupus erythematosus (LE) show a broad spectrum of clinicopathologic features. Histopathologically, besides typical patterns such as interface dermatitis, perivascular lymphocytic infiltrate and dermal mucin deposits, an involvement of the eccrine structures, especially the acrosyringium, may be observed. We describe the case of a 21-year-old woman with a 4-year history of systemic LE, who presented with a 'butterfly' rash over the cheeks as well as erythematous macules on the arms and décolleté. Biopsy from one lesion on the arm revealed interface changes, necrotic keratinocytes and exocytosis of lymphocytes restricted only to the regions of the acrosyringia. The epidermis between affected acrosyringia was normal with no hints of interface dermatitis. The eccrine glands and coils were not affected. In the dermis there were only sparse inflammatory infiltrates. Differential diagnoses such as erythema multiforme, drug eruption and lichen planus could be ruled out because of histopathologic features and clinical presentation. This is an example of a peculiar histopathological variant of cutaneous LE, characterized by exclusive involvement of the acrosyringia. The histopathologic features represent a pitfall in the diagnosis and can be correctly interpreted only upon correlation with clinical data.

Background Extranodal natural killer–/T-cell lymphoma, nasal type (ENKTCL-NT) is a highly aggressive lymphoma and prognosis is usually poor. The genetic background of primary cutaneous cases is poorly understood. Objective We sought to evaluate the clinicopathologic features of cutaneous ENKTCL-NT, and the prognostic significance of genomic copy number alterations. Methods Eight cases of cutaneous ENKTCL-NT (5 primary, 2 secondary, 1 no staging performed), including 2 patients with an unusually prolonged course of 5 and 23 years, were investigated using array comparative genomic hybridization. Results All patients presented with typical clinicopathologic features. Epstein-Barr virus was found in neoplastic cells in all specimens. Copy number alterations were detected in all 8 cases with losses on 6q (37.5% of cases) and 7p (37.5% of cases), and gains on 7q (37.5% of cases) being the most frequent. Complexity of array comparative genomic hybridization profile did not correlate with the course of the disease. However, an increase of copy number alterations was detected in sequential biopsy specimens of 1 long-term survivor. Limitations This was a small case series retrospective study. Conclusion Clinicopathologic features of cutaneous ENKTCL-NT are distinctive. Lower number of copy number alterations cannot be used as predictor for prolonged survival in cutaneous ENKTCL-NT.

Summary BAP1 (BRCA1-Associated Protein 1) was initially identified as a protein that binds to BRCA1. BAP1 is a tumour suppressor that is believed to mediate its effects through chromatin modulation, transcriptional regulation, and possibly via the ubiquitin-proteasome system and the DNA damage response pathway. Germline mutations of BAP1 confer increased susceptibility for the developmentofseveral tumours, including uveal melanoma, epithelioid atypical Spitz tumours, cutaneous melanoma, and mesothelioma. However, the complete tumour spectrum associated with germline BAP1 mutations is not yet known. Somatic BAP1 mutations are seen in cutaneous melanocytic tumours (epithelioid atypical Spitz tumours and melanoma), uveal melanoma, mesothelioma, clear cell renal cell carcinoma, and other tumours. Here, we review the current state of knowledge about the functional roles of BAP1 , and summarise data on tumours associated with BAP1 mutations. Awareness of these tumours will help pathologists and clinicians to identify patients with a high likelihood of harbouring germline or somatic BAP1 mutations. We recommend that pathologists consider testing for BAP1 mutations in epithelioid atypical Spitz tumours and uveal melanomas, or when other BAP1-associated tumours occur in individual patients. Tumour tissues may be screened for BAP1 mutations/loss/inactivation by immunohistochemistry (IHC) (demonstrated by loss of nuclear staining in tumour cells). Confirmatory sequencing may be considered in tumours that exhibit BAP1 loss by IHC and in those with equivocal IHC results. If a BAP1 mutation is confirmed in a tumour, the patient’s treating physician should be informed of the possibility of a BAP1 germline mutation, so they can consider whether genetic counselling and further testing of the patient and investigation of their family is appropriate. Recognition and evaluation of larger numbers of BAP1-associated tumours will also be necessary to facilitate identification of additional distinct clinico-pathological characteristics or other genotype-phenotype correlations that may have prognostic and management implications.

Purpose: Conjunctival melanoma is a rare but potentially deadly tumor of the eye. Despite effective local therapies, recurrence and metastasis remain frequent. Once the tumor has metastasized, treatment options are limited and the prognosis is poor. To date, little is known of the genetic alterations in conjunctival melanomas. Experimental Design: We conducted genetic analysis of 78 conjunctival melanomas, to our knowledge the largest cohort reported to date. An oncogene hotspot array was run on 38 samples, screening for a panel of known cancer-relevant mutations. Thirty tumors were analyzed for genome-wide copy number alterations (CNA) using array-based comparative genomic hybridization. Sanger sequencing of selected target mutations was conducted in all samples. Results: BRAF mutations were identified in 23 of 78 (29%) tumors. NRAS mutations, previously not recognized as relevant in conjunctival melanoma, were detected in 14 of 78 (18%) tumors. We found CNAs affecting various chromosomes distributed across the genome in a pattern reminiscent of cutaneous and mucosal melanoma but differing markedly from uveal melanoma. Conclusions: The presence of NRAS or BRAF mutations in a mutually exclusive pattern in roughly half (47%) of conjunctival melanomas and the pattern of CNAs argue for conjunctival melanoma being closely related to cutaneous and mucosal melanoma but entirely distinct from uveal melanoma. Patients with metastatic conjunctival melanoma should be considered for therapeutic modalities available for metastatic cutaneous and mucosal melanoma including clinical trials of novel agents. Clin Cancer Res; 19(12); 3143–52. ©2013 AACR.

Recently a group of spitzoid melanocytic proliferations with loss of BAP1 expression has been reported. The lesions may occur sporadically or as part of a familial cancer syndrome. They have distinct histopathologic features characterized by a nevus-like silhouette and cytologic composition of large epithelioid melanocytes with oval vesicular nuclei, distinct nucleoli, and abundant cytoplasm with well-defined cytoplasmic borders. A characteristic immunohistochemical finding is loss of nuclear labeling for BAP1. In contrast to classic Spitz nevi, the lesions carry the BRAF mutation. They may present as a pure large epithelioid cell proliferation or as a combined lesion in association with a conventional nevus. Here we report a series of 8 combined melanocytic lesions, in which a dominant large epithelioid cell proliferation with loss of BAP1 expression was associated and intimately admixed with a BAP1-positive conventional nevus. These biphenotypic lesions were from 6 patients, 3 female and 3 male, ranging in age from 16 to 59 years. Immunohistochemical analysis for BAP1 showed loss of nuclear labeling confined to the large epithelioid melanocyte subpopulation. The conventional melanocytes retained BAP1 expression. Both large epithelioid and conventional melanocytes were immunoreactive with the monoclonal antibody VE1, which recognizes the protein encoded by mutant BRAF. In 6 cases the conventional nevus component was a compound nevus of small "type B" melanocytes. In 2 cases, the nevus remnant was entirely intradermal. The lesions described herein may represent a peculiar combined melanocytic nevus variant. However, longer follow-up and more studies are needed to determine the biological potential of the BAP1-negative melanocyte proliferations.

Dermatofibroma (cutaneous fibrous histiocytoma) represents a common benign mesenchymal tumor, and numerous morphological variants have been described. Some variants of dermatofibroma are characterized by an increased risk of local recurrences, and there are a few reported metastasizing cases. Unfortunately, an aggressive behavior cannot be predicted reliably by morphology at the moment, and we evaluated the value of array-comparative genomic hybridization (CGH) in this setting. Seven cases of clinically aggressive dermatofibromas were identified, and pathological and molecular features were evaluated. The neoplasms occurred in four female and in three male patients (mean age was 33 years, range 2–65 years), and arose on the shoulder, buttock, temple, lateral neck, thigh, ankle, and cheek. The size of the neoplasms ranged from 1 to 9 cm (mean: 3 cm). An infiltration of the subcutis was seen in five cases. Two neoplasms were completely excised, whereas an incomplete or marginal excision was reported in the remaining cases. Local recurrences were seen in six cases (time to the first recurrence ranged from 8 months to 9 years). Metastases were noted between 3 months and 8 years after diagnosis in six patients. Two patients died of disease, and two patients are alive with disease. Histologically, the primary tumors showed features of cellular dermatofibroma (four cases), cellular/aneurysmal dermatofibroma (one case), atypical/cellular dermatofibroma (one case), and classical dermatofibroma (one case). Mitotic figures ranged from 3 to 25 per 10 high-power fields, and focal necrosis was present in five cases. Interestingly, malignant transformation from cellular dermatofibroma to an obvious spindle cell/pleomorphic sarcoma was seen in one primary and in one recurrent neoplasm. Five neoplasms showed chromosomal aberrations by array-CGH, suggesting that these changes may represent an additional diagnostic tool in the recognition of cases of dermatofibroma with a metastatic potential.

Fluorescence in situ hybridization (FISH) for the diagnosis of melanoma makes use of specific fluorescent probes to detect selected chromosomal alterations on paraffin-embedded tissue samples. To date, interpretation of FISH data has been based on numerical values generated by 2 different computational algorithms that of Abbott and that of Gerami. To further evaluate the value of FISH in the diagnosis of malignant melanoma, we selected 163 clinically and histologically unequivocal cases of malignant melanoma in a cohort of 575 melanocytic tumors and analyzed FISH data using the criteria of Abbott, Gerami, and new combined criteria. Depending on the used criteria, FISH was positive in the unequivocal malignant melanoma in 69.3% (113/163) of cases using the Abbott criteria, 74.2% (121/163) of cases using the Gerami criteria, and 82.2% (134/163) of cases using the combined criteria of Abbott and Gerami. Although use of all 3 criteria was associated with 100% FISH negativity in a cohort of 30 unequivocal benign melanocytic nevi, use of the combined criteria revealed more FISH-positive cases in ambiguous benign melanocytic lesions than the criteria of Abbott or Gerami alone: Abbott, 125 of 367; Gerami, 146 of 367; combined, 161 of 367. Furthermore, we show that 66% (8/12) of FISH-negative cases of unequivocal melanoma are positive when analyzed by array comparative genomic hybridization (aCGH), demonstrating that false-negative results remain despite the usage of the combined criteria for evaluation of FISH data. In these 8 FISH-negative aCGH-positive cases, copy number alterations were often located on chromosomes 9p, a chromosomal locus that is not targeted by the FISH probes currently used. In conclusion, the existing criteria for the evaluation of multicolor melanocytic FISH are limited by a nonnegligeable rate of false negativity that can be reduced by using newly proposed combined criteria but at the cost of increased detection of FISH positivity in ambiguous benign melanocytic lesions.

Melanocytic tumors in the central nervous system (CNS) include metastatic melanoma and less commonly primary melanocytic tumors, which usually arise from melanocytes of the leptomeninges. The latter include, in order of increasing biologic potential, melanocytomas, melanocytic neoplasms of intermediate grade/differentiation and primary melanomas.(2) Primary leptomeningeal melanocytic neoplasms belong to a larger taxonomic group of benign and malignant tumors arising from melanocytes that are not associated with epithelia. The group also includes blue nevi, melanomas arising in association with blue nevi (so-called “malignant blue nevi”), uveal nevi and uveal melanomas (4, 5, 7). Neoplasms in this group share morphologic features such as predominance of spindled and epithelioid cells, conspicuous pigmentation and absence of epithelial involvement, along with frequent mutations of GNAQ or GNA11, two closely related G-proteins of the Gq family that encode critical amino acids required for the GTPase function of the proteins. GNAQ or GNA11 mutations occur in a mutually exclusive pattern and affect codon 183 in exon 4 or codon 209 in exon 5 of either gene.(7) Mutations at these sites cripple enzymatic function and lead to a constitutively activated GTP-bound state. When in this state, GNAQ and GNA11 act as dominant-acting oncogenes that activate several critical signalling pathways including the MAP-kinase pathway (5, 7). A recent study reported mutations in exon 5 of GNAQ in 6/12 (50%) melanocytomas, 5 of which were in paraspinal locations.(3) We extended this analysis to include exons 4 and 5 of both GNAQ and GNA11. Five cases of CNS melanocytoma were identified from the consultation files of one of the authors (M.K.R.). Sections were cut from formalin-fixed, paraffin-embedded tumor tissue, and stained with hematoxylin-eosin; immunohistochemistry was performed. Tumor DNA was extracted from tissue carefully microdissected from deparaffinized, unstained sections. Direct (Sanger) sequencing for exons 4 and 5 of each of GNAQ and GNA11 was performed using methods described previously.(7) The clinical and pathologic features of the tumors are summarized in Table 1. The tumors occurred in 3 males and 2 females, with a median age of 42 years (range 29-61 years). They were composed of spindle-shaped, oval or epithelioid cells arranged in nests and vague whorls. Tumor cells ranged from amelanotic (Fig. 1a) to conspicuously pigmented (Fig. 1c). Immunohistochemically, all tumors were diffusely positive for S-100 and HMB-45, and negative for epithelial membrane antigen. Mutations were identified in exon 4 of GNAQ (1 case, Fig. 1b) and exon 5 of GNA11 (1 case, Fig. 1d). The mutations [GNAQ:(c.548G>A, p.(Arg183Gln) and GNA11:c.626A>C, p.(Gln209Pro)] are identical to those seen in uveal melanoma and intradermal melanocytic proliferations (6, 7). Our results expand the spectrum of GNAQ and GNA11 mutations that may occur in melanocytomas. To our knowledge, this is the first description of mutations in GNA11 and in exon 4 of GNAQ in melanocytomas. Figure 1 a) Case 1 – A monomorphous population of slightly spindled, amelanotic cells in vaguely whorling array is present (hematoxylin-eosin, x100). Inset - Diffuse cytoplasmic immunolabeling for HMB-45 confirms the melanocytic nature of the tumor cells ... TABLE Clinical and pathologic features of melanocytomas The occurrence of GNAQ and GNA11 mutations in melanocytomas,(3) dermal melanocytic tumors(6, 7) and uveal melanomas(6, 7) suggests the possibility of a developmental link between the cells of origin of these tumors. Indeed, this thesis is supported by the recent description of a developmental pathway in which a subgroup of melanocytes derives from Schwann cell precursors.(1) Although we identified a GNAQ exon 4 mutation in 1 of 5 cases of melanocytoma, exon 4 mutations in either GNAQ or GNA11 are rare in uveal melanomas (7/145, 4.8%) and blue nevi (2/96, 2.1%) (7). Mutational analysis of larger numbers of tumors is required to determine the true incidence of the different mutations in GNAQ and GNA11, and to investigate associations of specific mutations with clinical features, pathologic characteristics, and biologic behavior of melanocytomas.

Background Data on early lesions of primary cutaneous follicle center lymphoma (PCFCL), diffuse type are very limited. Objective We sought to elucidate the early clinicopathologic features of PCFCL, diffuse type. Methods Clinical, histologic, immunohistologic, molecular, and fluorescence in situ hybridization data from 24 patients with early lesions of PCFCL, diffuse type (male:female = 19:5; median age: 57 years) were determined. Results Lesions consisted mostly of solitary or clustered papules and small nodules located on the trunk (21 cases), arm (two cases), and scalp (one case). In 3 patients small papules were located at a distance from the main affected area. All biopsy specimens from early lesions showed aggregates of medium and large centrocytes admixed with small lymphocytes without formation of clear-cut lymph follicles. Staining for Bcl-2 was positive in only 7 cases, one revealing also a rearranged BCL2 signal by fluorescence in situ hybridization. Data on treatment and follow-up were available for 22 patients. At last examination 13 patients were in complete remission (median follow-up: 60 months), 6 were alive with skin disease alone (median follow-up: 60 months), two were alive with skin disease and bone-marrow or lymph node involvement, respectively, and one died of unrelated causes while in complete remission. Limitations The retrospective study and the fact that patients were treated at different institutions are limitations. Conclusions Early lesions of PCFCL, diffuse type present with characteristic clinicopathologic features. Dermatologists should be alert particularly to the early clinical manifestations of this lymphoma and to the presence of small, inconspicuous lesions at a distance from the main affected area in order to plan treatment properly.

In contrast to nodal large B-cell lymphomas, recurrent chromosomal aberrations have been studied only in a small number of cases of primary cutaneous diffuse large B-cell lymphoma (PCDLBCL). We investigated 25 PCDLBCLs (classified according to the WHO-EORTC classification into PCDLBCL, leg-type, 8; and PCDLBCL, other, 17), using an interphase fluorescence in situ hybridization technique. All cases were analyzed for chromosomal aberrations commonly observed in nodal large B-cell lymphomas, including structural aberrations of the genes BCL2, BCL6, and c-MYC, and numerical aberrations of the chromosomes/genes 3, 7, 8, 11, 12, 13, 17, 18q, RB1, and p53. We observed genetic aberrations in 19 (76%) of 25 patients. The most frequent numerical aberrations were gains of chromosome 12 (7 of 25, 28%), 7 (5 of 25, 20%), 3 (5 of 25, 20%), 18q (3 of 25, 12%), 11 (3 of 25, 12%), X (3 of 25, 12%), and losses of chromosome/gene 17/p53 (3 of 25, 12%). BCL2, c-MYC, and BCL6 were rearranged with the IGH gene in 4 (16%), 1 (4%), and none (0%) of 25 cases, respectively. Most aberrations were homogeneously distributed among cases of PCDLBCL, leg-type and of PCDLBCL, other, cases located on the leg or at other body sites, cases with round and cleaved cell morphology, and Bcl-2+ and Bcl-2- cases. These results suggest that PCDLBCLs show similar chromosomal aberrations irrespective of classification, anatomic site, cell morphology, and Bcl-2 expression, and that many similarities between primary cutaneous and nodal diffuse large B-cell lymphomas can be observed.

Importance Recently, a group of melanocytic tumors with loss of BAP1 expression has been described. The lesions may occur sporadically or as part of a familial cancer syndrome. They have distinct histopathologic features characterized by a nevuslike silhouette and cytologic composition of large epithelioid melanocytes with oval vesicular nuclei, distinct nucleoli, and abundant cytoplasm. The large melanocytes are immunohistochemically characterized by loss of nuclear labeling for BAP1. Observations We describe a 21-year-old patient with multiple combined melanocytic proliferations composed of both a nevus component with strong BAP1 expression and a large epithelioid melanocyte population with loss of BAP1 expression. The occurrence of multiple BAP1 loss melanocytic lesions raised concerns about a possible germline mutation. Sequence analysis of DNA from lesional and nonlesional skin confirmed a BAP1 germline mutation. Conclusions and Relevance The presence of multiple clinically banal–appearing melanocytic lesions with childhood onset suggests that the combined lesions with BAP1 loss large epithelioid melanocytes described herein are probably combined nevi. Our findings also illustrate how the detection of a histopathologically distinct melanocytic lesion, coupled with knowledge of its possible association with a hereditary tumor syndrome, can lead to the suspicion and confirmation of a germline mutation.

We recently reported that germline mutations in BAP1 cause a familial tumor syndrome characterized by high penetrance for melanocytic tumors with distinctive clinical and histologic features. Melanocytic neoplasms in affected individuals harbored BRAF mutations, showed loss of BAP1 expression, and histologically resembled so-called “atypical Spitz tumors” (ASTs). ASTs are an ill-defined and probably heterogenous group of melanocytic tumors that display histologic features seen in both Spitz nevi and melanomas. Their biologic behavior cannot be reliably predicted. Based on the histologic similarities of the familial tumors and ASTs, we hypothesized that a subset of ASTs might harbor genetic alterations seen in the familial tumors. To address this hypothesis, we analyzed 32 sporadic ASTs for BRAF mutations, and for BAP1 expression. To determine the utility of immunohistochemistry to assess BAP1 status, we analyzed samples from 42 patients with the above syndrome as well as 46 melanocytic nevi and found that loss of BAP1 expression was restricted to patients with the syndrome. Nine (28%) sporadic ASTs showed loss of BAP1 expression, of which of 8 (89%) had concomitant BRAF mutations. Only one of the BAP1-positive ASTs (4%) had a BRAF mutation (p Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3671. doi:1538-7445.AM2012-3671

Background Transepidermal melanocytic migration (TEM) is an important diagnostic criterion for malignancy, especially in association with cytologic atypia. However, TEM may also be observed in benign melanocytic tumors, such as Spitz nevus, acral nevi, or nevi in infancy. We discuss the value of TEM for the diagnosis of melanocytic tumors in a young patient previously diagnosed as having 11 cutaneous melanomas. Observation A 17-year-old patient with a history of 11 cutaneous melanomas diagnosed in the past 3 years by different expert dermatopathologists presented in our department. The previous histological diagnoses of melanoma were mainly based on the presence of important TEM. A reevaluation of all histological specimens in light of the clinical context and the lack of genomic aberrations as detected by array-comparative genomic hybridization led to a revision of the previous diagnoses. The striking TEM observed represents, in our opinion, a constitutional element of the melanocytic nevi in this patient and not a marker of malignancy. Conclusion Awareness of this finding is important to avoid overdiagnosis of melanoma in cases of melanocytic nevi.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare, clinically aggressive malignancy with a median survival of 12-14 months. To identify pathogenetic relevant genomic aberrations and molecular targets for therapy, we analyzed skin biopsy samples obtained from 14 patients using high-resolution array-based comparative genomic hybridization and immunostaining. Losses of chromosomes 9, 12, 13, and 15 were detected most frequently. Loss of the CDKN1B locus was the most common finding and was detected in 64% of tumors. In all but one case, the dose-dependent haploinsufficient cell-cycle inhibitor p27(KIP1), encoded by CDKN1B, was weakly expressed in the nuclei of tumor cells. Losses of the CDKN2A-ARF-CDKN2B locus occurred in 50% of patients, and in one case a distinct biallelic loss was identified. The cell-cycle inhibitor p16(INK4a), which is encoded by CDKN2A, was not expressed in tumor cells, suggesting a complete loss of function. Loss of chromosome 13, including the RB1 gene, was observed in 43% of tumors. These results imply that alterations of the cell-cycle checkpoint controlling proteins p27(KIP1), p16(INK4a), and RB1 may exert a profound effect in malignant transformation in BPDCN. The elucidation of the affected pathways may guide the development of new treatments specifically designed for this aggressive disease entity.