Superficial Wnt-Activated Melanocytic Nevi/Melanocytomas With a Junctional Component: A Case Series.

ABSTRACT: The conventional morphological characteristics of Wnt-activated deep penetrating/plexiform melanocytomas/nevi (DPN) are those of large spindled or epithelioid melanocytes with distinctive voluminous amphophilic cytoplasm, fine pigmented granules, and surrounding melanophages. The central molecular hallmark is the activation of the Wnt-pathway predominantly driven by mutations in the beta-catenin (CTNNB1) gene. Although typically lacking a junctional component, a lesser-known superficial variant with a junctional component has been identified, which could potentially lead to diagnostic challenges. This study presents a cohort of 11 such cases displaying a junctional component of DPN from 10 patients (5 women and 5 men; age range: 27-78 years; median age: 51 years). The nevi were distributed as follows: 1 conjunctival, 1 scalp, 2 lower limb, and 6 truncal lesions. Eight cases were combined with a conventional nevus, 2 cases displayed pure DPN cytology exhibiting only a junctional element, and 9 cases exhibited some degree of lentiginous architecture. All cases demonstrated a low mitotic index (<1 mitosis/mm2). Immunohistochemistry revealed positive BRAF V600E staining in 8 cases (8/11), whereas all cases tested (11/11) were PRAME negative. Nuclear beta-catenin and LEF1 staining was consistently strong and diffuse with DPN cytology (11/11), along with robust cyclin D1 staining in all cases tested (11/11). By contrast, all 9 conventional nevi showed an absence of nuclear beta-catenin staining (0/9) and weaker, mosaic-type LEF1 and cyclin D1 staining was observed. This study emphasizes the diagnostic challenge these nevi can pose in the absence of a conventional, deeper DPN component, which can potentially be misdiagnosed as melanoma.

In Situ Protein Expression Analysis of Melanocyte Differentiation Antigen TRP1 (Tyrosinase-Related Protein-1).

ABSTRACT: Melanocyte differentiation antigens refer to molecules expressed in cells of melanocytic lineage such as gp100/PMEL, tyrosinase, and Melan-A. Corresponding antibodies such as HMB45, T311, and A103 have become key immunohistochemical tools in surgical pathology for the diagnosis of pigmented and related lesions. Little is known about tyrosinase-related protein 1 (TRP1), another melanocyte differentiation antigen, which is an enzymatic component of melanogenesis and known as the brown locus in mice. In this study, we tested several commercial reagents to TRP1 and identified one clone, EPR13063, which we further characterized by testing its specificity and usefulness for surgical pathology. Subsequently, we analyzed the expression of TRP1 in panels of normal tissues and tumors. TRP1 is regularly expressed in normal skin and in cutaneous nevi predominantly present in junctional and to a lesser extent in dermal nevocytes. In melanoma, TRP1 is present in 100% and 44% of primary and metastatic melanomas, respectively. TRP1 was absent in 5 desmoplastic melanomas but heterogeneously present in 9 of 11 PEComas/angiomyolipomas. No TRP1 was found in neoplasms of nonmelanocytic lineage. We demonstrate that EPR13063 is a valuable reagent for the analysis of TRP1 expression in archival surgical pathology material. The TRP1 expression pattern in melanocytic and related lesions appears to parallel other melanocyte differentiation antigens with a higher incidence in primary and a lower incidence in metastatic melanomas.

Extramammary Paget disease. Part I. epidemiology, pathogenesis, clinical features, and diagnosis.

Extramammary Paget disease (EMPD) is a rare skin cancer of apocrine-rich skin that mimics common inflammatory and infectious dermatoses, leading to delays in diagnosis and increased patient morbidity. Better clinical recognition of this entity, multidisciplinary patient assessment, and deeper understanding of the underlying pathophysiology are essential to improve patient care and disease outcomes. It is important to distinguish primary intraepithelial/micro-invasive EMPD from invasive EMPD or cases with adenocarcinoma arising within EMPD. This 2-part continuing medical education series provides a complete picture of EMPD. Part 1 of this continuing medical education series reviews the epidemiology, oncogenesis, clinical and histopathologic presentation, workup, and prognosis of this rare cancer.

Mixed histiocytic neoplasms: A multicentre series revealing diverse somatic mutations and responses to targeted therapy.

Histiocytic neoplasms are diverse clonal haematopoietic disorders, and clinical disease is mediated by tumorous infiltration as well as uncontrolled systemic inflammation. Individual subtypes include Langerhans cell histiocytosis (LCH), Rosai-Dorfman-Destombes disease (RDD) and Erdheim-Chester disease (ECD), and these have been characterized with respect to clinical phenotypes, driver mutations and treatment paradigms. Less is known about patients with mixed histiocytic neoplasms (MXH), that is two or more coexisting disorders. This international collaboration examined patients with biopsy-proven MXH with respect to component disease subtypes, oncogenic driver mutations and responses to conventional (chemotherapeutic or immunosuppressive) versus targeted (BRAF or MEK inhibitor) therapies. Twenty-seven patients were studied with ECD/LCH (19/27), ECD/RDD (6/27), RDD/LCH (1/27) and ECD/RDD/LCH (1/27). Mutations previously undescribed in MXH were identified, including KRAS, MAP2K2, MAPK3, non-V600-BRAF, RAF1 and a BICD2-BRAF fusion. A repeated-measure generalized estimating equation demonstrated that targeted treatment was statistically significantly (1) more likely to result in a complete response (CR), partial response (PR) or stable disease (SD) (odds ratio [OR]: 17.34, 95% CI: 2.19-137.00, p = 0.007), and (2) less likely to result in progression (OR: 0.08, 95% CI: 0.03-0.23, p < 0.0001). Histiocytic neoplasms represent an entity with underappreciated clinical and molecular diversity, poor responsiveness to conventional therapy and exquisite sensitivity to targeted therapy.

The Impact of Next-generation Sequencing on Interobserver Agreement and Diagnostic Accuracy of Desmoplastic Melanocytic Neoplasms.

Next-generation sequencing (NGS) is increasingly being utilized as an ancillary tool for diagnostically challenging melanocytic neoplasms. It is incumbent upon the pathology community to perform studies assessing the benefits and limitations of these tools in specific diagnostic scenarios. One of the most challenging diagnostic scenarios faced by skin pathologists involves accurate diagnosis of desmoplastic melanocytic neoplasms (DMNs). In this study, 20 expert melanoma pathologists rendered a diagnosis on 47 DMNs based on hematoxylin and eosin sections with demographic information. After submitting their diagnosis, the experts were given the same cases, but this time with comprehensive genomic sequencing results, and asked to render a diagnosis again. Identification of desmoplastic melanoma (DM) improved by 7%, and this difference was statistically significant ( P <0.05). In addition, among the 15 melanoma cases, in the pregenomic assessment, only 12 were favored to be DM by the experts, while after genomics, this improved to 14 of the cases being favored to be DM. In fact, some cases resulting in metastatic disease had a substantial increase in the number of experts recognizing them as DM after genomics. The impact of the genomic findings was less dramatic among benign and intermediate-grade desmoplastic tumors (BIDTs). Interobserver agreement also improved, with the Fleiss multirater Kappa being 0.36 before genomics to 0.4 after genomics. NGS has the potential to improve diagnostic accuracy in the assessment of desmoplastic melanocytic tumors. The degree of improvement will be most substantial among pathologists with some background and experience in bioinformatics and melanoma genetics.

BRAF Mutated and Morphologically Spitzoid Tumors, a Subgroup of Melanocytic Neoplasms Difficult to Distinguish From True Spitz Neoplasms.

Drivers of Spitz neoplasms include activating point mutations in HRAS and Spitz-associated genomic fusions. It has become evident that some BRAF -mutated melanocytic neoplasms can morphologically mimic Spitz tumors (STs). These have been termed BRAF mutated and morphologically spitzoid (BAMS). In this study, 17 experts from the International Melanoma Pathology Study Group assessed 54 cases which included 40 BAMS and 14 true STs. The participants reviewed the cases blinded to the genomic data and selected among several diagnostic options, including BAMS, ST, melanoma, and other. A total of 38% of all diagnostic selections in the BAMS cases were for BAMS, whereas 32% were for ST. In 22 of the BAMS cases, the favored diagnosis was BAMS, whereas in 17 of the BAMS cases, the favored diagnosis was ST. Among the 20 cases in the total group of 54 with the highest number of votes for ST, half were BAMS. Of BAMS, 75% had a number of votes for ST that was within the SD of votes for ST seen among true ST cases. There was poor interobserver agreement for the precise diagnosis of the BAMS (kappa = 0.16) but good agreement that these cases were not melanoma (kappa = 0.7). BAMS nevi/tumors can closely mimic Spitz neoplasms. Expert melanoma pathologists in this study favored a diagnosis of ST in nearly half of the BAMS cases. There are BAMS cases that even experts cannot morphologically distinguish from true Spitz neoplasms.

ATOH1, TFAP2B, and CEACAM6 as Immunohistochemical Markers to Distinguish Merkel Cell Carcinoma and Small Cell Lung Cancer.

Merkel cell carcinoma (MCC) and small cell lung cancer (SCLC) can be histologically similar. Immunohistochemistry (IHC) for cytokeratin 20 (CK20) and thyroid transcription factor 1 (TTF-1) are commonly used to differentiate MCC from SCLC; however, these markers have limited sensitivity and specificity. To identify new diagnostic markers, we performed differential gene expression analysis on transcriptome data from MCC and SCLC tumors. Candidate markers included atonal BHLH transcription factor 1 (ATOH1) and transcription factor AP-2ß (TFAP2B) for MCC, as well as carcinoembryonic antigen cell adhesion molecule 6 (CEACAM6) for SCLC. Immunostaining for CK20, TTF-1, and new candidate markers was performed on 43 MCC and 59 SCLC samples. All three MCC markers were sensitive and specific, with CK20 and ATOH1 staining 43/43 (100%) MCC and 0/59 (0%) SCLC cases and TFAP2B staining 40/43 (93%) MCC and 0/59 (0%) SCLC cases. TTF-1 stained 47/59 (80%) SCLC and 1/43 (2%) MCC cases. CEACAM6 stained 49/59 (83%) SCLC and 0/43 (0%) MCC cases. Combining CEACAM6 and TTF-1 increased SCLC detection sensitivity to 93% and specificity to 98%. These data suggest that ATOH1, TFAP2B, and CEACAM6 should be explored as markers to differentiate MCC and SCLC.

A cutaneous epithelioid vascular tumor harboring a TPM3::ALK fusion.

Substantial progress has been made in understanding the molecular pathways associated with vascular tumors over the last two decades. In addition to mutations and copy number aberrations, fusions have emerged as significant contributors to the pathogenesis of a notable subset of vascular tumors. In this report, we present a case of an unusual intradermal vascular tumor with epithelioid cytomorphology. Immunohistochemistry revealed diffuse positivity for CD31, ERG and Factor VIII, supporting its endothelial lineage. RNA sequencing (ArcherFusion Plex) revealed the presence of an in-frame fusion between the genes TPM3 Exon 8 and ALK Exon 20. Immunohistochemistry confirmed ALK expression by the endothelial cells. To our knowledge, this is the first documented case of a vascular tumor harboring an ALK fusion. It may fall within the spectrum of epithelioid hemangiomas; nevertheless, we cannot definitively exclude the possibility of it being a distinct and potentially unique benign entity on its own.

Spindle cell porocarcinoma with a novel YAP1::MAML3 fusion.

Porocarcinomas are rare sweat gland cancers representing the malignant counterpart to benign poromas. Their diagnosis can be challenging, especially in the absence of an associated poroma or when the tumor is poorly differentiated. Since recurrent YAP1::MAML2 and YAP1::NUTM1 fusions have been identified in poroid tumors, molecular studies provide an opportunity to support the diagnosis in challenging cases. We describe a case of a female patient in her early 90s, with a polypoid mass of the hip. Histopathologically, there was a poorly differentiated malignant spindle cell tumor adjacent to a poroma. Because of the close association with a poroma and immunoreactivity for p40, a diagnosis of spindle cell porocarcinoma was rendered, which was further supported by YAP1 immunohistochemical studies. Antibodies targeting both the N-terminus and C-terminus confirmed YAP1 rearrangement in both the poroma and the spindle cell neoplasm. Subsequent targeted RNA sequencing revealed a YAP1::MAML3 gene fusion. MAML3 has previously not yet been reported as a YAP1 fusion partner in porocarcinoma. With the illustration of a rare spindle cell variant of porocarcinoma and the identification of a novel gene fusion, this case report expands the spectrum of morphologic and genomic aberrations associated with porocarcinoma.

Perifollicular linear projections: A dermatoscopic criterion for the diagnosis of lentigo maligna on the face.

BACKGROUND: Lentigo maligna (LM) can mimic benign, flat, pigmented lesions and can be challenging to diagnose. OBJECTIVE: To describe a new dermatoscopic feature termed "perifollicular linear projections (PLP)" as a diagnostic criterion for LM on the face. METHODS: Retrospective study on reflectance confocal microscopy and dermatoscopy images of flat facial pigmented lesions originating from 2 databases. PLP were defined as short, linear, pigmented projections emanating from hair follicles. Dermatoscopy readers were blinded to the final histopathologic diagnosis. RESULTS: From 83 consecutive LMs, 21/83 (25.3%) displayed "bulging of hair follicles" on reflectance confocal microscopy and 18 of these 21 (85.7%), displayed PLP on dermatoscopy. From a database of 2873 consecutively imaged and biopsied lesions, 252 flat-pigmented facial lesions were included. PLP was seen in 47/76 melanomas (61.8%), compared with 7/176 lesions (3.9%) with other diagnosis (P < .001). The sensitivity was 61.8% (95% CI, 49.9%-72.7%), specificity 96.0% (95% CI, 92.9%-98.4%). PLP was independently associated with LM diagnosis on multivariate analysis (OR 26.1 [95% CI, 9.6%-71.0]). LIMITATIONS: Retrospective study. CONCLUSION: PLP is a newly described dermatoscopic criterion that may add specificity and sensitivity to the early diagnosis of LM located on the face. We postulate that PLP constitutes an intermediary step in the LM progression model.

Most large structural variants in cancer genomes can be detected without long reads.

Short-read sequencing is the workhorse of cancer genomics yet is thought to miss many structural variants (SVs), particularly large chromosomal alterations. To characterize missing SVs in short-read whole genomes, we analyzed 'loose ends'-local violations of mass balance between adjacent DNA segments. In the landscape of loose ends across 1,330 high-purity cancer whole genomes, most large (>10-kb) clonal SVs were fully resolved by short reads in the 87% of the human genome where copy number could be reliably measured. Some loose ends represent neotelomeres, which we propose as a hallmark of the alternative lengthening of telomeres phenotype. These pan-cancer findings were confirmed by long-molecule profiles of 38 breast cancer and melanoma cases. Our results indicate that aberrant homologous recombination is unlikely to drive the majority of large cancer SVs. Furthermore, analysis of mass balance in short-read whole genome data provides a surprisingly complete picture of cancer chromosomal structure.

Immunohistochemistry for PRAME in Dermatopathology.

ABSTRACT: Preferentially expressed antigen in melanoma (PRAME) is a tumor-associated antigen first identified in a melanoma patient and found to be expressed in most melanomas as well as in variable levels in other malignant neoplasms of epithelial, mesenchymal, or hematolymphoid lineage. Detection of PRAME expression in formalin-fixed paraffin-embedded tissue is possible by immunohistochemistry (IHC) with commercially available monoclonal antibodies. In situ and invasive melanoma frequently show a diffuse pattern of nuclear PRAME immunoreactivity which contrasts with the infrequent and typically nondiffuse staining seen in nevi. In many challenging melanocytic tumors, results of PRAME IHC and other ancillary tests correlate well, but not always: The tests are not interchangeable. Most metastatic melanomas are positive for PRAME, whereas nodal nevi are not. Numerous studies on PRAME IHC have become available in the past few years with results supporting the value of PRAME IHC as an ancillary tool in the evaluation of melanocytic lesions and providing insights into limitations in sensitivity and specificity as well as possible pitfalls that need to be kept in mind by practicing pathologists.

Acquired Melanocytic Nevi Mimicking Acral Lentiginous Melanoma in a Patient Taking a BRAF Inhibitor.

This case report describes a patient in their 60s with metastatic colon cancer who developed multiple new dark nevi within 2 months of initiating encorafenib and panitumumab therapy.

Cutaneous Neuroendocrine Mucinous Carcinomas Are Low-grade But May Be Associated With Other Cancers.

Primary cutaneous mucinous sweat gland carcinoma is said to be prognostically stratifiable by neuroendocrine differentiation, however, this assertion is based on historical data and older staining techniques. We aimed to evaluate the percentage of mucinous and nonmucinous adnexal tumors expressing the newer, more sensitive neuroendocrine marker insulinoma-associated protein 1 (INSM1), and to assess clinicopathologic features in patients cohorted by this phenotype. Of 12 available adnexal/cutaneous adenocarcinomas, 9 were mucinous, 3/9 of which were INSM1-negative, and 2/3 with nodal metastases. Of 3 nonmucinous cases, all were INSM1-negative, 1/3 with nodal metastasis, and 2/3 with lymphovascular invasion. In contrast, of 6 mucinous INSM1-positive cases, no cases had LVI or metastasis, however, 3 patients died during follow-up, 2 from breast or urothelial cancer. A fourth patient developed breast carcinoma. INSM1-positive tumors, from cheek (3), scalp (2), and chin (1) were estrogen receptor and progesterone receptor positive. No cases of apocrine adenoma or hidrocystoma, basal cell, or sebaceous carcinoma labeled with INSM1. While most primary cutaneous mucinous carcinomas are of the neuroendocrine type, our study confirms the presence of occasional non-neuroendocrine mucinous carcinomas. We validate the association of such tumors and nonmucinous non-neuroendocrine adnexal carcinoma with intermediate-grade behavior, including lymph node metastases, but not death. Conversely, neuroendocrine expressing primary cutaneous mucinous carcinoma may represent the well-differentiated neuroendocrine neoplasm/neuroendocrine tumor primary to skin, with low-grade behavior, but attendant risk of germline susceptibility to other aggressive extracutaneous tumors. Routine assessment of cutaneous adnexal carcinoma with INSM1 and longer term follow-up and cancer screening of patients with positive staining is recommended.

Association of functional, inherited vitamin D-binding protein variants with melanoma-specific death.

BACKGROUND: It is unclear whether genetic variants affecting vitamin D metabolism are associated with melanoma prognosis. Two functional missense variants in the vitamin D-binding protein gene (GC), rs7041 and rs4588, determine 3 common haplotypes, Gc1s, Gc1f, and Gc2, of which Gc1f may be associated with decreased all-cause death among melanoma patients based on results of a prior study, but the association of Gc1f with melanoma-specific death is unclear. METHODS: We investigated the association of the Gc1s, Gc1f, and Gc2 haplotypes with melanoma-specific and all-cause death among 4490 individuals with incident, invasive primary melanoma in 2 population-based studies using multivariable Cox-proportional hazards regression. RESULTS: In the pooled analysis of both datasets, the patients with the Gc1f haplotype had a 37% lower risk of melanoma-specific death than the patients without Gc1f (hazard ratio [HR] = 0.63, 95% confidence interval [CI] = 0.47 to 0.83, P = .001), with adjustments for age, sex, study center, first- or higher-order primary melanoma, tumor site, pigmentary phenotypes, and Breslow thickness. Associations were similar in both studies. In pooled analyses stratified by Breslow thickness, the corresponding melanoma-specific death HRs for those patients with the Gc1f haplotype compared with those without Gc1f were 0.89 (95% CI = 0.63 to 1.27) among participants with tumor Breslow thickness equal to or less than 2.0 mm and 0.40 (95% CI = 0.25 to 0.63) among participants with tumor Breslow thickness greater than 2.0 mm (Pinteraction = .003). CONCLUSIONS: Our findings suggest that individuals with the GC haplotype Gc1f may have a lower risk of dying from melanoma-specifically from thicker, higher-risk melanoma-than individuals without this Gc1f haplotype.

Sex-Specific Associations of MDM2 and MDM4 Variants with Risk of Multiple Primary Melanomas and Melanoma Survival in Non-Hispanic Whites.

MDM2-SNP309 (rs2279744), a common genetic modifier of cancer incidence in Li-Fraumeni syndrome, modifies risk, age of onset, or prognosis in a variety of cancers. Melanoma incidence and outcomes vary by sex, and although SNP309 exerts an effect on the estrogen receptor, no consensus exists on its effect on melanoma. MDM2 and MDM4 restrain p53-mediated tumor suppression, independently or together. We investigated SNP309, an a priori MDM4-rs4245739, and two coinherited variants, in a population-based cohort of 3663 primary incident melanomas. Per-allele and per-haplotype (MDM2_SNP309-SNP285; MDM4_rs4245739-rs1563828) odds ratios (OR) for multiple-melanoma were estimated with logistic regression models. Hazard ratios (HR) for melanoma death were estimated with Cox proportional hazards models. In analyses adjusted for covariates, females carrying MDM4-rs4245739*C were more likely to develop multiple melanomas (ORper-allele = 1.25, 95% CI 1.03-1.51, and Ptrend = 0.03), while MDM2-rs2279744*G was inversely associated with melanoma-death (HRper-allele = 0.63, 95% CI 0.42-0.95, and Ptrend = 0.03). We identified 16 coinherited expression quantitative loci that control the expression of MDM2, MDM4, and other genes in the skin, brain, and lungs. Our results suggest that MDM4/MDM2 variants are associated with the development of subsequent primaries and with the death of melanoma in a sex-dependent manner. Further investigations of the complex MDM2/MDM4 motif, and its contribution to the tumor microenvironment and observed associations, are warranted.

PRAME Immunohistochemical Expression and TERT Promoter Mutational Analysis as Ancillary Diagnostic Tools for Differentiating Proliferative Nodules From Melanoma Arising in Congenital Nevi.

ABSTRACT: Proliferative nodules (PNs) are benign melanocytic proliferations that typically develop within congenital melanocytic nevi. These tumors have overlapping histological features with melanoma. Ancillary immunohistochemistry and genomic sequencing are often used in diagnostically challenging cases. To assess the utility of preferentially expressed antigen in melanoma (PRAME) immunoreactivity and telomerase reverse transcriptase (TERT) promoter mutation analysis in distinguishing PNs from melanoma arising in congenital nevi cases. Twenty-one PNs and 2 melanomas arising in congenital nevi were immunohistochemically stained with PRAME. Cases with adequate tissue were also assessed for TERT promoter mutations through sequencing studies. The positivity rates in the PN cases were compared with those of the melanomas. Two of 21 PN cases were diffusely positive for PRAME (≥75% of the tumor cells positive). Two of 2 melanomas arising in congenital nevus cases were also diffusely PRAME positive. The difference was statistically significant using a Fisher exact test. None of the tumors harbored TERT promoter mutations. PRAME immunohistochemical marker may have diagnostic value in distinguishing diagnostically challenging PNs from melanoma, but diffuse expression is not specific for melanoma.