Molecular analysis has emerged as an important ancillary method for the diagnosis and treatment of melanocytic tumors. Test results are often helpful but can occasionally be confounding if an unfamiliar variant is identified. We report a series of melanocytic tumors, which were found to harbor a TFG gene fusion and their significance. Of 105 melanocytic tumors with gene fusions, 9 involved TGF (8.6%). One tumor harbored a TFG::NTRK3 fusion, more precisely characterized as an NTRK3 fusion with TFG as the 5' partner, the detection of which was diagnostically helpful by indicating the presence of a Spitz pathway. Eight cases exhibited a TFG::ADGRG7 fusion. Current evidence suggests that this recurrent event represents a polymorphic germline variant, possibly arising from read-through transcription (intergenic splicing), rather than a biologically pathogenic driver. It should be noted that laboratory reporting practices vary, and not all laboratories report such transcripts in official molecular pathology reports. Recognition of such fusions is essential to avoid misinterpretation, particularly as fusion detection increasingly informs diagnosis and clinical decision-making. These findings underscore the necessity of integrating molecular results with established clinicopathologic frameworks.

Melanomas are immunogenic with significant variation of tumor infiltrating lymphocytes (TIL). Primary melanomas are routinely scored by pathologists, for TIL grade, as brisk, nonbrisk, and absent, but TIL grade is not utilized in staging. While brisk TIL grade predicts improved melanoma-specific survival, nonbrisk TIL grade often lacks prognostic significance. A high proportion of primary melanomas from stage II and III patients are scored as nonbrisk TIL grade. Our goal is to quantitatively predict T cell estimates in primary melanoma from DNA methylation data using immunofluorescence CD3 + staining as ground truth. Primary cutaneous melanomas (n = 80), analyzed for multiplex-immunofluorescence (CD3, CD8, S100) and whole-genome DNA methylation, underwent elastic net modeling of the proportion of CD3 + T lymphocytes to build a quantitative prediction model for TILs in primary melanoma called EpiTIL. Melanoma-specific survival (MSS) Kaplan–Meier curves significantly differed by primary melanoma EpiTIL tertiles (p = 0.001). Patients with intermediate or highest tertile EpiTIL scores had higher median probability of MSS than those with lowest tertile scores. EpiTIL added significant prognostic value for MSS beyond age, sex, and stage, analyzed using proportional hazard regression modelling (p = 0.012). EpiTIL survival prediction was validated in two multi-omic studies, TCGA (n = 352) and InterMEL (n = 399). Among TCGA melanomas, the survival curves significantly differed by EpiTIL tertile scores (p = 0.009) and EpiTIL scores added prognostic value to clinical factors (p < 0.002). In the InterMEL case–control study of stage II/III melanoma, patients with 5-year MSS without recurrence (controls) had a significantly higher mean EpiTIL scores than those who died of melanoma within 5 years (cases) (p = 1.5e − 11). Using logistic regression, EpiTIL scores significantly predicted 5-year MSS without recurrence, even after adjusting for age, sex, stage and TIL grade, with OR = 4.7 (p = 2.38e-06) comparing the highest to lowest EpiTIL tertiles. Extending the EpiTIL prediction to the Newell metastatic melanoma cohort, we found immune checkpoint inhibitor responders had a significantly higher mean EpiTIL score than non-responders (p = 0.047). EpiTIL is a DNA methylation-based predictor of T cell proportion that demonstrates potential prognostic value in primary melanoma, particularly for stages II and III. Furthermore, higher EpiTIL scores derived from primary melanomas were positively associated with improved therapeutic responses to immune checkpoint inhibitors in metastatic disease, highlighting its potential to identify patients most likely to benefit from immunotherapy.

Abstract: BAP1 inactivated melanocytomas are considered intermediate grade melanocytic tumors. They may have overlapping morphologic features with melanoma. Nuclear atypia, expansile growth, and mitotic activity often raise concern for the possibility of melanoma. However, there is limited information in the literature on outcomes-based diagnostic criteria that may be useful for the distinction of BAP1 inactivated melanocytomas from BAP1 inactivated melanomas. Herein, we present a series of 20 BAP1 inactivated melanomas with clinical follow-up (n = 17) and compare the genomic and morphologic features with 23 BAP1 inactivated melanocytomas. In this series, only BAP1 inactivated melanomas had ulceration, tumor necrosis, invasion of the subcutis, and mitotic activity ≥4/mm 2 . BAP1 inactivated melanomas had more pathogenic variants on average than BAP1 inactivated melanocytomas (6.6 vs. 2.4, P = 0.0001) and a higher TMB (31.2 m/Mb vs. 7.8 m/Mb, P = 0.0071). Pathogenic variants in TERT -promoter, CDKN2A , CDK4 , MYC , the SWI/SNF complex, and the PI3K-AKT pathway were only seen in BAP1 inactivated melanomas. Because BAP1 inactivated melanomas are uncommon compared with BAP1 inactivated melanocytomas, useful diagnostic criteria must have very high specificity and be rare to absent in BAP1 inactivated melanocytomas. In this study, we identified morphologic and molecular features that were strongly associated with BAP1 inactivated melanomas but not seen in BAP1 inactivated melanocytomas. Our findings may be helpful for the diagnostic assessment of challenging melanocytic tumors with BAP1 inactivation.

Since the original description of CRTC1::TRIM11 fusion cutaneous tumors (CTCT) in 2018, an increasing number of cases with metastatic behavior have been reported, yet there are limited studies analyzing prognostic parameters. This expanding data set presents an opportunity for reappraisal of clinical behavior. We present a series of 21 cases with detailed morphologic, molecular, clinical outcomes, and therapeutic response data. We utilize this data and a meta-analysis of all the cases in the literature to assess potential prognostic parameters to assist in clinical management. Primary tumors resulting in metastasis were larger ( P =0.038), had higher mitotic counts ( P <0.001), were more frequently ulcerated ( P =0.001), and exclusively harbored TERT promoter mutations ( P =0.005). A functional analysis of mixed data demonstrated a clear clustering pattern in which metastatic cases had larger diameters and were more mitotically active compared with nonmetastatic cases. Inclusion of TERT promoter mutational status further improved the model. There were no metastatic events among cases meeting all the following criteria: size <1.2 cm, <7 mitoses/mm 2 , and absent TERT promoter mutation. Metastatic events frequently involved regional lymph nodes, and all patients with distant metastasis had pulmonary involvement. Considering metastatic events in 23% of cases, sentinel lymph node biopsy and imaging studies may be considered in some cases, while, in cases with smaller size, low mitotic counts, and no evidence of a TERT promoter mutation, excision alone may be adequate. Given poor therapeutic responses in reported metastatic cases, more therapeutic options should be explored.

PURPOSE:Neoadjuvant PD-1 blockade has shown marked efficacy before surgery in patients with head and neck cutaneous squamous cell cancinoma (CSCC). However, the potential for PD-1 blockade as a definitive, nonoperative therapy remains uncertain. EXPERIMENTAL DESIGN:We conducted a single-institution retrospective study (2018 to 2023) of patients with locally advanced resectable stage III/IV CSCC treated with cemiplimab. Patients received neoadjuvant cemiplimab followed by surgery or cemiplimab monotherapy without surgery. The primary endpoint was the objective radiologic response rate (assessed using immune Response Evaluation Criteria in Solid Tumors) and clinical response rate; the secondary endpoints included disease-specific survival (DSS), progression-free probability (PFP), histopathologic response, and exploratory genomic biomarkers. RESULTS:Fifty-one patients received cemiplimab monotherapy alone (median age: 78.8 years), and 21 received neoadjuvant cemiplimab followed by surgery (median age: 73 years). The 2-year DSS and PFP for cemiplimab monotherapy were 90% [95% confidence interval (CI), 80%-100%] and 82% (95% CI, 72%-94%), respectively. The 2-year DSS and PFP for neoadjuvant cemiplimab with surgery were 95% (95% CI, 86%-100%) and 78% (95% CI, 62%-100%), respectively. Tumor-infiltrating lymphocytes (TIL) were higher in patients with complete response (CR) or partial response (PR) than in patients with progressive disease (PD) or stable disease (P = 0.005, q = 0.026), with absent TILs more frequent in nonresponders. Tumor mutational burden was higher in CR (55.7) and PR (14.9) than in PD (4.9; P = 0.02, q = 0.04). CONCLUSIONS:In this retrospective, nonrandomized cohort, definitive-intent cemiplimab monotherapy was associated with durable disease control in selected patients with locally advanced resectable head and neck CSCC. This study provides a promising real-world organ preservation experience for patients with advanced head and neck CSCC treated with cemiplimab monotherapy that does not compromise oncologic outcomes.

BACKGROUND:Neoadjuvant therapy with immune checkpoint inhibitors (ICIs) is increasingly used in advanced or recurrent melanoma based on outcomes observed in clinical trials. The efficacy and toxicity of this in a real-world setting remain unclear. STUDY DESIGN:We conducted a retrospective review of adults with cutaneous melanoma who received neoadjuvant ICI as first line therapy at our institution between 2019 and 2024. Patients had advanced melanoma that was surgically resectable and treated with neoadjuvant intent. The primary outcome was pathological response, with a secondary outcome of immune-related toxicity. RESULTS:In total, 81 patients were identified. The median age was 64 (range: 21-86). There were 48 males. Most patients received 2 cycles (n = 53) prior to resection (range: 1-7 cycles). Dual ICI was the most common approach (n = 62). Disease stage ranged from IIC to IV, with 57% IIIC. Half were pathologic non-responders (n = 41). Pathologic complete response (pCR) was seen in 25% (n = 20), near-pCR in 2% (n = 2) and partial PR in 10% (n = 8). Ten (12%) patients had a discrepant PR between two or more resected sites. Immune related adverse events were observed in 34 (42%) patients; 21 (26%) grade 1-2, and 13 (16%) grade 3-4. Overall survival trended towards significance (p = 0.07) for those with mPR. CONCLUSIONS:Non-trial use of neoadjuvant ICI therapy is associated with a less favourable pathological response than reported in clinical trials and similar risks of toxicity.

BAP1 inactivated melanocytic tumors (BIMTs) are recognized for their potential for significant morphologic atypia including nuclear atypia, expansile growth, and mitotic activity, making it difficult to form firm morphologic criteria for malignancy. Next generation sequencing (NGS) is becoming increasingly utilized in melanocytic pathology. We conducted a two-phase survey with 26 dermatopathologists from the International Melanoma Pathology Study Group to assess the impact of NGS on diagnostic accuracy and interobserver agreement in 31 BIMTs. After NGS results, interobserver agreement improved from fair on Survey 1 (κ = 0.348) to moderate on Survey 2 (κ = 0.441). Respondents were 1.7 times more likely to be correct on Survey 2 after NGS results (OR = 1.67, 95% CI [1.16-2.44], p = 0.005). When accounting for case variability and difficulty, respondents were 8.7 times more likely to provide a correct diagnosis for a given case (CMH OR = 8.69, 95% CI [4.89-15.44], p < 0.001). Among the 8 BAP1 inactivated melanomas in this study, 3 transitioned from a majority of votes for benign/intermediate grade BIMT to a majority of votes for melanoma after seeing NGS data. Genomic aberrations exclusive to malignant cases included pathogenic variants in TERT-p, CDKN2A, PTEN, and amplification of MYC. Our study suggests NGS has the potential to improve diagnostic accuracy and interobserver agreement for BAP1 inactivated melanocytic tumors. With the advent of increasingly effective therapies for melanoma, there is value in forming a definitive diagnosis of melanoma when appropriate. Additional studies with greater case numbers and follow-up are needed to further validate these findings.

In the past 2 decades, several molecular methods have been developed as an adjunct for the assessment of melanocytic neoplasms. Some tests can assist in the diagnostic workup of neoplasms with ambiguous histopathologic findings. Others can optimize the selection of patients for targeted therapy. Some tests also aim to provide prognostic information. Scenarios when ordering these tests may be appropriate and helpful are discussed in this article as well as pitfalls in the interpretation of test results. Due to the inherent limitations in sensitivity and specificity of various tests, correlation with the histopathologic findings is paramount.

Cribriform tumor of the skin (formerly primary cutaneous cribriform carcinoma/primary cutaneous cribriform apocrine carcinoma) is a rare adnexal neoplasm of uncertain malignant potential. Recent studies have identified recurrent co-deletion of the long arm of chromosomes 6 and 9 and CD38 overexpression as potential diagnostic features, but their sensitivity and specificity remain incompletely defined. We identified 11 cribriform tumors with classic morphologic features, including several previously reported molecular characterized cases and additional unpublished cases, from multiple institutions. CD38 immunohistochemistry was performed on all tumors and compared with a panel of morphologic mimics, including adenoid cystic carcinoma (n = 8), digital papillary adenocarcinoma (n = 8), eccrine/apocrine adenomas (n = 7), hidradenoma (n = 2), and endocrine mucin-producing sweat gland carcinoma (n = 3). SNP array analysis was available in nine cases. Patients had a median age of 47 years with a slight female predominance (64

Digital papillary adenocarcinoma (DPA) is a rare malignant sweat gland tumor affecting fingers and toes most commonly. Human papillomavirus type 42 (HPV42), a low-risk HPV type, is an important diagnostic criterion. No uniform mutational signature has been detected in DPA except for BRAF mutations encoding p.V600E in small case series and in single case reports. The aim of this study was to add to the data on the prevalence of low-risk HPV/HPV42 detection and BRAF-VE1 immunohistochemistry in digital papillary adenocarcinoma. H and E-stained sections and immunohistochemistry for S100, SOX10, SMA, p63/p40, CK7, CK5/6, YAP1, and BRAF-VE1 were reviewed, and in situ hybridization (ISH) for low-risk HPV (including HPV42) or specifically HPV42 was performed. Clinical follow-up was obtained from patient records. Twenty-eight tumors were included and presented on the fingers (23), feet (4), and vulva (1) with a median size of 1.5 cm. The patient age ranged from 11 to 88 years (median: 49.5; M:F=6:1). Histopathologically, digital papillary adenocarcinomas presented as multinodular, poorly- or well-circumscribed tumors in the dermis and subcutaneous tissue, with solid, cystic, and papillary growth patterns. Cytologic atypia was mild to moderate. All tumors were positive for low-risk HPV and/or HPV42. BRAF-VE1 immunohistochemistry was negative in all tumors. Two patients developed distant metastases; all other patients were alive without recurrence (median follow-up: 46.5 mo, range: 5 to 192 mo). In conclusion, this study does not support the pathogenic role of BRAF p.V600E in digital papillary adenocarcinoma but confirms low-risk HPV/HPV42 infection as the only driver in all tumors.

A comprehensive understanding of newly described tumors is often an evolutionary process. In this study, we describe the extended spectrum of morphologic patterns in a cohort of 144 ALK fusion Spitz neoplasms and provide the largest data set of ALK fusion Spitz with clinical follow-up. In addition to the most classic morphologic pattern of a nodular silhouette with wavy fascicles of spindle cells, these tumors may also form a desmoplastic pattern, a combined nevus of Reed-Spitz pattern, a predominantly epithelioid pattern, and a nevoid pattern. There are genomic correlates to some of these morphologic patterns, with Reed-Spitz cases frequently having TPM4 as the fusion partner ( P =0.001), epithelioid cases frequently having EHBP1 as the fusion partner ( P =0.0002), and nevoid cases frequently having KIF5B as the fusion partner. Two fusion partners, ZEB2 and EML4 , were only seen in Spitz melanoma (SM) cases. TERT promoter mutations and c-MYC amplification were only seen in SM. A meta-analysis of the literature suggests that adverse events tend to be associated with c-MYC amplification, CDKN2A homozygous deletion, and higher mitotic count (5.5 mitoses/mm 2 in metastatic cases vs. 2.2 mitoses/mm 2 in nonmetastatic cases). Our study expands the morphologic spectrum and the associated genomic correlates of ALK -rearranged Spitz neoplasms and identifies parameters associated with malignant behavior.

Introduction: Uveal melanomas are rare and usually detected in adults over 60 years old. We presented herein an unusual intraocular melanocytic tumor that does not fit into any known category in a child with 10-year follow-up data. The clinical findings, course, ultrasound, MRI, and pathology, including immunohistochemistry and gene profiling, of a child with pigmented intraocular masses simulating uveal melanoma are described. The tumor is provisionally called “endopapillary uveal melanocytic tumor of childhood” based on its unusual pathology and molecular biology. Comprehensive molecular testing, including MSK-IMPACT, which interrogates 468 known cancer genetic alterations, and Archer fusion testing (RNA sequence analysis) revealed no abnormalities. Case Presentation: Our patient was a 7-month-old white boy with a suspected mass in the left eye. There was no family history of melanoma. An MRI scan revealed a 1.9 × 1.7-cm well-circumscribed, heterogeneously T1 pre-contrast hyperintense mass, which demonstrated heterogeneous low signal intensity on T2-weighted imaging. A needle biopsy using a 25-gauge needle revealed a pigmented tumor, so we performed an enucleation. Upon histopathologic examination after enucleation, the tumor was densely pigmented, without significant necrosis or internal cavitation. Tumor cells grew around vascular “papillae.” Six years later, the patient is alive and shows no evidence of local or systemic recurrence. Conclusion: Our case exhibited unique features and pathology, without any of the known genetic abnormalities associated with uveal melanoma and does not match the descriptions in the existing literature. Thus, we have named these masses “endopapillary uveal melanocytic tumor of childhood.”

Supplementary data depicted in Supplementary Figures S1-S9

BACKGROUND:Recent genome-wide association studies (GWAS) have identified new susceptibility loci for melanoma, but their associations with multiple primary melanoma (MPM) are unclear. METHODS:We investigated the associations of 69 SNPs in 39 GWAS-identified loci with odds of MPM relative to single primary melanoma in the international, population-based Genes, Environment, and Melanoma study. Per-minor-allele ORs and 95% confidence intervals (CI) for individuals with MPM "cases" (n = 1,205) relative to single primary melanoma "controls" (n = 2,458) were estimated using multivariable logistic regression, and polygenic risk scores (PRS) were calculated and weighted based on a 2020 GWAS meta-analysis (57 of the 68 independent GWAS SNPs available). RESULTS:Thirteen SNPs in 11 gene regions (PARP1, CYP1B1/RMDN3, TERT, RAPGEF5, TYRP1, MTAP, CDKN2A/CDKN2B, KLF4, TYR, SOX6, and ASIP) were statistically significantly associated (P < 0.05) with MPM adjusting for age, sex, age-by-sex interaction, and study center. The highest versus lowest PRS quintile was associated with a 2.81-fold higher odds of MPM (95% CI, 2.10-3.78; P = 7.5 × 10-13); this association was attenuated but remained statistically significant after excluding SNPs individually associated with MPM (OR = 1.75, 95% CI, 1.32-2.31). CONCLUSIONS:Inherited genetic variants spanning 11 gene regions were independently associated with MPM. Nonsignificant SNPs were associated with MPM when aggregated into a PRS, indicating that their cumulative effect may influence MPM risk despite lacking individual statistical significance in our study population. IMPACT:Our findings provide additional evidence that these loci are associated with melanoma risk and estimate the magnitude of their genetic effect on subsequent (multiple) primary melanoma risk.

HPV42 is associated with DPA. A, Overview of unbiased screening approach for detection of vertebrate-infecting viruses in targeted next-generation sequencing (NGS) data. Targeted NGS data from 18 skin tumor types and MCC (positive control, pos. ctrl.) were analyzed with the centrifuge metagenomic classifier utilizing a custom viral database (Viral DB). B, Virus abundance score in targeted NGS data of 214 human tumor samples. Detection of HPV42 in 100% (n = 11/11) of DPA samples. ACC, adenoid cystic carcinoma; AFX, atypical fibroxanthoma; AS, angiosarcoma; BPDCN, blastic plasmacytoid dendritic cell neoplasm; DM, desmoplastic melanoma; DTE, desmoplastic trichoepithelioma; EPC, eccrine porocarcinoma; ES, eccrine spiradenoma; LM, lentigo maligna melanoma; MAC, microcystic adnexal carcinoma; PM, pediatric melanoma; PPT, proliferating pilar cystic tumor; SAC, spiradenocarcinoma; SC, sebaceous carcinoma; SGC, sweat gland carcinoma; SKCM, cutaneous melanoma. Viral prevalence: proportion of samples with detected virus in any given tumor type. Abundance score: mean proportion of detected virus in any given tumor type. C, HPV42 abundance score in a cohort of 17 DPAs after sequence capture to DNA and RNA of 6,453 viruses. White diamond: HPV42 detected but below an abundance of 1%. ND, not determined. D, Top, Circos plot depicting HPV42–human genome breakpoints. Each arch represents one detected breakpoint. Bottom, lollipop presentation of integration breakpoints in the HPV42 genome. Each lollipop represents one breakpoint (Supplementary Table S4). E, FISH signal of HPV42 genome (magenta) and human genome integration site adjacent locus (yellow) in DPA nuclei (blue). White arrowheads indicate fusion signals. Scale bar, 2.5 μm. Individual channels and quantifications in Supplementary Fig. S4. F, Top, RNA-ISH staining for expression of early region HPV42 mRNA in lung metastasis of a DPA tumor (T) and the surrounding normal (N) tissue. Scale bar, 1 mm. Bottom, inset. Scale bar, 20 μm.

In this Special Issue of the Journal of Cutaneous Pathology in memory of Dr. Martin C. Mihm, Jr, we highlight his many contributions over more than 50 years to the catalog of specific melanocytic tumor terminology. Dr. Mihm was an active participant in the International Melanoma Pathology Study Group (IMPSG). Discussions led to proposed recommendations for changes in the terminology of melanocytic tumors and their standardized diagnostic reporting. Histopathological reports of melanocytic tumors provide critical information that guides patient counseling and therapy. Importantly the pathology report must relay whether the melanocytic tumor is benign, intermediate, or malignant, and when appropriate, indicate diagnostic and/or prognostic uncertainty. Recent shifts in diagnostic terminology include the recommended use of the term "melanocytoma" to describe a morphologically and genetically defined subset of intermediate risk melanocytic tumors with higher (although still very low) risk of progression compared with benign nevi. Melanocytomas are distinguished from melanocytic tumors of uncertain malignant potential (MELTUMP) which are histopathologically indeterminate or uncertain tumors. In the setting of a broad lexicon for the reporting of melanocytic tumors, an assessment tool has been developed to map existing diverse terminologies into distinct hierarchical classes. The Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis (MPATH-Dx) V2.0 provides a four-tiered classification scheme that is tiered by risk of tumor progression and recommended treatment. The purpose of this review is to report these shifts in diagnostic terminology, discussed and reviewed at the annual workshop of the IMPSG, in Edinburg, Scotland, in November 2022. This discussion included the use of the term melanocytoma, and the use of the MPATH-Dx V2.0 classification and terminology for melanocytic tumors. Dr. Mihm was diligent in his attention to specific terminology, in his memory we aim to recommend terminology that improves communication in the care of those diagnosed with melanocytic tumors.

INTRODUCTION:Merkel cell carcinoma (MCC) is an uncommon neuroendocrine cutaneous malignancy considered to have a high risk of local recurrence (LR). We investigated the true risk of LR in patients with MCC treated by surgical excision alone. PATIENTS AND METHODS:Patients with clinically localized MCC excised with pathologically negative surgical margins were identified from a prospectively maintained single-institution database from November 1980 through December 2022. The cumulative incidence of LR, defined as recurrence within 5 cm of the surgical scar, was estimated using death as a competing event. RESULTS:Among 447 patients, 393 (88%) were treated with surgery alone, and 54 (12%) also received adjuvant radiotherapy (RT) to the primary site. LR occurred in eight patients, with seven recurrences detected within 12 months of treatment. All recurrences occurred in patients treated with surgery alone for a 1-year LR rate of 1.8% (95% confidence interval [CI] 0.8-3.6%). At a median follow-up of 8.8 years (95% CI 7.6-10) from presentation, of the six patients with LR alone, all treated with surgery and/or RT, four patients had no evidence of disease and two died of other causes. Two patients developed distant metastases at the time of LR; both received systemic therapy and died of disease. The low incidence of LR precluded analysis of risk factors. CONCLUSIONS:Negative-margin surgery without adjuvant RT provides excellent local control, with an LR rate of 1.8%. LR was effectively treated with surgery and/or RT. These data do not support the routine use of adjuvant RT for all patients after complete excision of primary MCC.