The clinicopathologic spectrum and genomic landscape of de-/trans-differentiated melanoma

Metastatic Nodular Melanoma with Angiosarcomatous Transdifferentiation-A Case Report and Review of the Literature

Diagnosing cutaneous melanomas relies mainly on histopathological analysis, which, in selected cases, can be aided by immunohistochemical evaluation of conventional melanocytic markers. Nevertheless, these malignancies, particularly in metastatic settings, may display divergent differentiation with unusual histological and immunohistochemical features. In this context, we present the case of a 65-year-old male diagnosed with typical superficial spreading melanoma who developed recurrence and metastatic lesions featuring angiosarcomatous differentiation. The diagnosis of the initial tumour and the subsequently dedifferentiated lesions was confirmed by ample immunohistochemical analysis, which included several melanocytic markers, as well as mesenchymal and vascular markers. The recurrent tumour and lymph nodes metastases were completely negative for Melan-A and PRAME, and focally positive for SOX10. Additionally, they also displayed diffuse, intense positivity for CD10 and WT1 and focal positivity for CD99, ERB, and CD31. Thus, the diagnosis of primary cutaneous melanoma with recurrent and metastatic divergent angiosarcomatous differentiation was established. This occurrence is particularly rare and can pose important diagnostic challenges. Therefore, in addition to presenting this highly unusual case, we also performed a comprehensive review of the literature on divergent differentiation in melanomas.

Metastatic Undifferentiated Melanoma Mimicking a Primary Bone Tumor: A Potential Diagnostic Pitfall

ABSTRACT

Undifferentiated melanoma (UM) is defined by the loss of classic morphologic and immunohistochemical melanocytic markers. Reports in the literature are rare and show that UM usually occurs as a metastasis in the setting of a known primary cutaneous melanoma. The most common mutations in UM include those involving BRAF , NRAS , and KIT , which are almost invariably present in the parent melanoma. In this study, we report a case of a primary sinonasal melanoma with metastatic UM presenting with osteoclast-like giant cells and resembling a primary bone tumor. The retention of an unusual KRAS mutation in UM that was also present in the primary lesion provided critical information for the diagnosis. Our report highlights the importance of considering mutational analysis to identify undifferentiated melanomas in patients with metastatic tumors which do not have the typical histopathologic and immunohistochemical features of melanoma.

The practical utility of AI-assisted molecular profiling in the diagnosis and management of cancer of unknown primary: an updated review

Cancer of unknown primary (CUP) presents a complex diagnostic challenge, characterized by metastatic tumors of unknown tissue origin and a dismal prognosis. This review delves into the emerging significance of artificial intelligence (AI) and machine learning (ML) in transforming the landscape of CUP diagnosis, classification, and treatment. ML approaches, trained on extensive molecular profiling data, have shown promise in accurately predicting tissue of origin. Genomic profiling, encompassing driver mutations and copy number variations, plays a pivotal role in CUP diagnosis by providing insights into tumor type-specific oncogenic alterations. Mutational signatures (MS), reflecting somatic mutation patterns, offer further insights into CUP diagnosis. Known MS with established etiology, such as ultraviolet (UV) light-induced DNA damage and tobacco exposure, have been identified in cases of dedifferentiated/transdifferentiated melanoma and carcinoma. Deep learning models that integrate gene expression data and DNA methylation patterns offer insights into tissue lineage and tumor classification. In digital pathology, machine learning algorithms analyze whole-slide images to aid in CUP classification. Finally, precision oncology, guided by molecular profiling, offers targeted therapies independent of primary tissue identification. Clinical trials assigning CUP patients to molecularly guided therapies, including targetable alterations and tumor mutation burden as an immunotherapy biomarker, have resulted in improved overall survival in a subset of patients. In conclusion, AI- and ML-driven approaches are revolutionizing CUP management by enhancing diagnostic accuracy. Precision oncology utilizing enhanced molecular profiling facilitates the identification of targeted therapies that transcend the need to identify the tissue of origin, ultimately improving patient outcomes.

Divergent Lineage Markers in Anaplastic Thyroid Carcinoma

Anaplastic thyroid carcinoma (ATC) often results from dedifferentiation of differentiated thyroid carcinoma (DTC), and the diagnosis is not difficult, as the tumor is seen to progress from a recognized DTC. However, in some cases, the diagnosis based on biopsy of limited tissue or resection of a completely undifferentiated tumor relies on immunohistochemical biomarkers and is usually a diagnosis of exclusion. To examine the biomarker profile of ATC and to determine whether divergent lineage markers can complicate this process, we examined the expression of a number of biomarkers in a series of ATCs. Cases retrieved from the department laboratory information system were included if there was evidence of an accurate diagnosis based on the presence of a coexisting or antecedent DTC or in cases where the immunoprofile was consistent with thyroid origin in a non-equivocal clinical setting. Questionable cases were excluded. We identified 36 cases for analysis. Tissue sections were stained for PAX8, TTF1, BRAFV600E, NRASQ61R, TRK, and p53, as well as p40, CDX2, SATB2, GATA3, CD117, CD163, SALL4, SMARCA4, PRAME, SOX10, ERG and HEPPAR1. As expected, all 36 ATCs were negative for TTF1 except for one showing focal, weak expression. Thirteen expressed PAX8 with variable intensity. BRAFV600E was positive in 10/34 tumors and equivocal in 3; NRASQ61R was positive in 12, and TRK was positive in 1 case. Staining for p53 was diffusely positive in 14 and completely negative in 19, with only 3 cases showing a wild-type pattern. We found aberrant expression of GATA3 in 11/36 cases, SATB2 in 8/36, CD117 in 2/35, and SALL4 in 1/30. CD163 expression was identified in tumor cells in 10/30 cases with variable intensity; in the other tumors, interpretation was obscured by abundant histiocytes. P40 was positive in 5 cases with squamoid morphology. CDX2 was negative in 35 tested cases. PRAME was identified in 1 of 33 cases. Stains for SOX10, ERG, and HEPPAR1 were negative in 33 cases. Twenty tested cases showed retained SMARCA4 expression. We conclude that ATCs express a number of divergent lineage markers that can cause diagnostic dilemmas, as they are also features of other tumors in the differential diagnosis of high-grade midline neck malignancies.

PRAME Expression Is a Useful Tool in the Diagnosis of Primary and Metastatic Dedifferentiated and Undifferentiated Melanoma

Although mostly recognized in the metastatic setting dedifferentiated and undifferentiated melanomas are increasingly recognized as cutaneous and, less commonly, mucosal primary tumors. Their diagnosis is challenging and dependent on sampling and recognition of a conventional melanoma precursor and/or detection of a mutation in a conventional melanoma driver gene. PRAME immunohistochemistry has recently become an important ancillary tool in the separation of melanoma from benign nevi, but no comprehensive studies exist regarding its value in the detection of dedifferentiated and undifferentiated melanomas and their separation from atypical fibroxanthoma and pleomorphic dermal sarcoma, the main differential diagnoses on sun-damaged skin. After retrieval from archival files, we performed PRAME immunohistochemistry on 11 primary and 10 metastatic dedifferentiated and undifferentiated melanomas, 11 atypical fibroxanthomas, and 10 pleomorphic dermal sarcomas. Nuclear staining was assigned extent (ranging from 0 to 4 and reflecting the percentage of PRAME-positive tumor nuclei) and intensity scores (graded as absent, weak, moderate, and strong, with assigned scores ranging from 0 to 3) with combined scores ranging from 0 to 7. Both primary and metastatic dedifferentiated and undifferentiated melanomas showed strong and diffuse nuclear PRAME staining with median combined scores of 7. Strong and diffuse staining was also seen in all conventional melanoma precursors except for desmoplastic melanoma. In contrast, PRAME staining in atypical fibroxanthoma and pleomorphic dermal sarcoma was patchy and weak with median combined scores of 2. Our data emphasize the diagnostic utility of PRAME staining as a first screening tool in the detection and workup of dedifferentiated and undifferentiated melanomas, both in the primary and metastatic settings. PRAME immunohistochemistry is particularly helpful as it is also positive in tumors without a recognizable conventional melanoma precursor and in those associated with desmoplastic melanomas, where PRAME is typically found to be negative.

Melanoma with rhabdomyosarcomatous features: a potential diagnostic pitfall

Malignant melanoma is well-known for phenotypic plasticity, and rare cases of divergent differentiation have been described. This case report is of a tumour diagnosed as 'rhabdomyosarcoma' on the face of a man in his 80s. However, given the recent excision of an ulcerated melanoma (Breslow thickness 5.8 mm) from the same site, the more likely diagnosis would be recurrent melanoma with rhabdomyosarcomatous differentiation. This highlights a rare form of divergent differentiation and a potential diagnostic pitfall.

Dedifferentiated and undifferentiated melanomas: a practical approach to a challenging diagnosis

Dedifferentiation, defined as the loss of cellular features of terminal differentiation resulting in a more primitive, unspecialized phenotype, is a rare phenomenon in melanoma and more commonly observed in the metastatic setting than in primary melanomas. The diagnosis of dedifferentiated melanoma poses a significant challenge, and the tumors need to be carefully sampled and worked up to identify any residual morphologic, immunohistochemical, or molecular evidence of their melanocytic lineage. This article reviews our current knowledge of the clinical, histopathological, immunohistochemical, and molecular features of these rare tumors and provides a practical diagnostic approach and discussion of the relevant differential diagnoses and associated diagnostic pitfalls.

Pleomorphic Dermal Sarcoma With Metastasis to the Lung: A Case Report

ABSTRACT

Atypical fibroxanthoma and pleomorphic dermal sarcoma (PDS) are dermal malignant mesenchymal tumors that lie at the ends of the same disease spectrum. Clinically indistinguishable from atypical fibroxanthoma, PDS has a more aggressive course with significantly higher rate of local recurrence and metastases. Histological findings that favor a PDS include subcutaneous invasion, tumor necrosis, lymphovascular invasion, and/or perineural infiltration. Herein, we report a case of PDS with metastasis to the lung. Our report highlights the risk of local recurrence and metastatic spread in this cutaneous tumor and the importance of distinguishing this entity from its less aggressive counterpart.

The Comparative Pathology Workbench: Interactive visual analytics for biomedical data

Pathologists need to compare histopathological images of normal and diseased tissues between different samples, cases, and species. We have designed an interactive system, termed Comparative Pathology Workbench (CPW), which allows direct and dynamic comparison of images at a variety of magnifications, selected regions of interest, as well as the results of image analysis or other data analyses such as scRNA-seq. This allows pathologists to indicate key diagnostic features, with a mechanism to allow discussion threads amongst expert groups of pathologists and other disciplines. The data and associated discussions can be accessed online from anywhere in the world. The Comparative Pathology Workbench (CPW) is a web-browser-based visual analytics platform providing shared access to an interactive "spreadsheet" style presentation of image and associated analysis data. The CPW provides a grid layout of rows and columns so that images that correspond to matching data can be organised in the form of an image-enabled "spreadsheet". An individual workbench can be shared with other users with read-only or full edit access as required. In addition, each workbench element or the whole bench itself has an associated discussion thread to allow collaborative analysis and consensual interpretation of the data. The CPW is a Django-based web-application that hosts the workbench data, manages users, and user-preferences. All image data are hosted by other resource applications such as OMERO or the Digital Slide Archive. Further resources can be added as required. The discussion threads are managed using WordPress and include additional graphical and image data. The CPW has been developed to allow integration of image analysis outputs from systems such as QuPath or ImageJ. All software is open-source and available from a GitHub repository.

Undifferentiated and Dedifferentiated Metastatic Melanomas Masquerading as Soft Tissue Sarcomas: Mutational Signature Analysis and Immunotherapy Response

The distinction between undifferentiated melanoma (UM) or dedifferentiated melanoma (DM) from undifferentiated or unclassifiable sarcoma can be difficult and requires the careful correlation of clinical, pathologic, and genomic findings. In this study, we examined the utility of mutational signatures to identify patients with UM/DM with particular attention as to whether this distinction matters for treatment because the survival of patients with metastatic melanoma has dramatically improved with immunologic therapy, whereas durable responses are less frequent in sarcomas. We identified 19 cases of UM/DM that were initially reported as unclassified or undifferentiated malignant neoplasm or sarcoma and submitted for targeted next-generation sequencing analysis. These cases were confirmed as UM/DM by harboring melanoma driver mutations, UV signature, and high tumor mutation burden. One case of DM showed melanoma in situ. Meanwhile, 18 cases represented metastatic UM/DM. Eleven patients had a prior history of melanoma. Thirteen of 19 (68%) of the tumors were immunohistochemically completely negative for 4 melanocytic markers (S100, SOX10, HMB45, and MELAN-A). All cases harbored a dominant UV signature. Frequent driver mutations involved BRAF (26%), NRAS (32%), and NF1 (42%). In contrast, the control cohort of undifferentiated pleomorphic sarcomas (UPS) of deep soft tissue exhibited a dominant aging signature in 46.6% (7/15) without evidence of UV signature. The median tumor mutation burden for DM/UM vs UPS was 31.5 vs 7.0 mutations/Mb (P < .001). A favorable response to immune checkpoint inhibitor therapy was observed in 66.6% (12/18) of patients with UM/DM. Eight patients exhibited a complete response and were alive with no evidence of disease at the last follow-up (median 45.5 months). Our findings support the usefulness of the UV signature in discriminating DM/UM vs UPS. Furthermore, we present evidence suggesting that patients with DM/UM and UV signatures can benefit from immune checkpoint inhibitor therapy.

Clinical, histopathological and molecular features of dedifferentiated melanomas: An EORTC Melanoma Group Retrospective Analysis

PURPOSE

Dedifferentiated melanoma (DedM) poses significant diagnostic challenges. We aimed to investigate the clinical, histopathological and molecular features of DedM. Methylation signature (MS) and copy number profiling (CNP) were carried out in a subgroup of cases.

PATIENTS AND METHODS

A retrospective series of 78 DedM tissue samples from 61 patients retrieved from EORTC (European Organisation for Research and Treatment of Cancer) Melanoma Group centres were centrally reviewed. Clinical and histopathological features were retrieved. In a subgroup of patients, genotyping through Infinium Methylation microarray and CNP analysis was carried out.

RESULTS

Most patients (60/61) had a metastatic DedM showing most frequently an unclassified pleomorphic, spindle cell, or small round cell morphology akin to undifferentiated soft tissue sarcoma, rarely associated with heterologous elements. Overall, among 20 successfully analysed tissue samples from 16 patients, we found retained melanoma-like MS in only 7 tissue samples while a non-melanoma-like MS was observed in 13 tissue samples. In two patients from whom multiple specimens were analysed, some of the samples had a preserved cutaneous melanoma MS while other specimens exhibited an epigenetic shift towards a mesenchymal/sarcoma-like profile, matching the histological features. In these two patients, CNP was largely identical across all analysed specimens, in line with their common clonal origin, despite significant modification of their epigenome.

CONCLUSIONS

Our study further highlights that DedM represents a real diagnostic challenge. While MS and genomic CNP may help pathologists to diagnose DedM, we provide proof-of-concept that dedifferentiation in melanoma is frequently associated with epigenetic modifications.

Primary Undifferentiated/Dedifferentiated Cutaneous Melanomas-A Review on Histological, Immunohistochemical, and Molecular Features with Emphasis on Prognosis and Treatment

Diagnosing cutaneous melanoma is usually straightforward based on these malignancies' histopathological and immunohistochemical features. Nevertheless, melanomas can imitate various other neoplasms, sometimes lacking the expression of conventional melanocytic markers and expressing non-melanocytic ones. Furthermore, divergent differentiation is more often encountered in metastatic melanomas and is still poorly described in primary cutaneous melanomas, and little is known about these patients' prognosis and therapeutic approach. Therefore, we reviewed the literature on undifferentiated/dedifferentiated cutaneous melanomas, and we discuss the histological, immunohistochemical, and molecular profiles of undifferentiated/dedifferentiated cutaneous melanomas to understand these peculiar lesions better and improve their diagnostic algorithm. In addition to this, we also discuss how different genetic mutations may influence prognosis and become potential therapeutic targets.

Primary cutaneous extraskeletal osteosarcoma: a series of 16 cases

Extraskeletal osteosarcoma (EOS) is a high grade soft tissue tumour characterised by the production of malignant osteoid, without attachment/involvement of underlying bone/periosteum. Rarely, EOS presents as a cutaneous tumour. The clinical behaviour of primary cutaneous EOS (PC-EOS) remains incompletely characterised. Herein we present the largest case series of PC-EOS reported to date. Sixteen PC-EOS cases from the archives/consultation files were retrieved (male:female 1:1; age 31-96 years, mean age 66 years). The tumours measured 1-10 cm (mean 3.2 cm) and were located on the lower extremity (7), head (6), upper extremity (2), and trunk (1). They consisted of pleomorphic, spindled-to-epithelioid cells, with fascicular, nodular, or sheet-like growth patterns and foci of malignant osteoid. Immunohistochemistry did not reveal specific lines of differentiation, and there was no evidence of other tumour types. A literature review was conducted to identify all well characterised cases of PC-EOS. A combined analysis of present and past cases was performed to determine overall trends in clinical characteristics and outcomes. The mean follow-up period was 23.9 months, during which 67.5% of patients experienced progression-free survival and 18% of patients died of disease. Rates of local recurrence and metastasis were 10% and 25%, respectively, approximately double past estimates. These data suggest that the prognosis of PC-EOS is less favourable than previously thought. The differential diagnosis includes benign entities (e.g., ossifying pyogenic granuloma) and malignant neoplasms with heterologous osteosarcomatous differentiation (e.g., carcinosarcoma, transdifferentiated melanoma). Wide excision remains the standard of care, and the role of chemotherapy and radiation remains inconclusive. Recognition of this rare entity can facilitate prompt diagnosis and appropriate treatment.

CHRNA1 and its correlated-myogenesis/cell cycle genes are prognosis-related markers of metastatic melanoma

Nicotinic acetylcholine receptors (CHRNs) expression and their critical role in various types of cancer have been reported. However, it is still unclear which CHRNs and their associated genes play essential roles in metastasis in melanoma patients. Here, we performed bioinformatics analyses on publicly available bulk RNA sequencing (RNA-seq) data of patients with melanoma to identify the CHRNs highly expressed in metastatic melanoma. We found that CHRNA1 was highly expressed in metastatic melanoma samples compared to primary melanoma samples and was strongly associated with CHRNB1 and CHRNG. These muscle-type CHRNs (CHRNA1, CHRNB1, and CHRNG) were correlated with the ZEB1 and Rho/ROCK pathway-related genes in metastatic melanoma samples. Pairwise correlations and enrichment analyses revealed that CHRNA1 was significantly associated with myogenesis/muscle contraction and cell cycle genes. Kaplan-Meier curves illustrated the involvement of CHRNA1, four of its correlated genes (DES, FLNC, CDK1, and CDC20), and the myogenesis gene signature in the prognosis of melanoma patients. Following the bulk RNA-seq analysis, single-cell RNA-seq (scRNA-seq) analysis showed that the CHRNA1-expressing melanoma cells are primarily metastatic and had high expression levels of CHRNB1, CHRNG, and myogenesis/cell cycle-related genes. Our bioinformatics analyses of the bulk RNA-seq and scRNA-seq data of patients with melanoma revealed that CHRNA1 and its correlated myogenesis/cell-related cycle genes are critical prognosis-related markers of metastatic melanoma.

Primary cutaneous malignant melanoma with rhabdomyosarcomatous differentiation originating from a melanocytic nevus in a patient with myelodysplastic syndrome

Malignant melanoma (MM) may rarely exhibit divergent differentiation, in which melanocytic markers may be lost, leading to difficulty in diagnosis. A 64-year-old man recently diagnosed with myelodysplastic syndrome complained of development of a nodule in a melanocytic nevus on his scalp. On histopathologic examination, junctional nevus nests and diffuse cellular infiltrations with a sheet-like growth pattern of pleomorphic epithelioid cells were observed in the upper dermis. Junctional nevus cells were S-100 positive, and pleomorphic epithelioid cells extending from the junctional nests were weakly positive for S-100. Large polygonal cells with eccentric nuclei and intracytoplasmic hyaline inclusions were observed in the mid to deep dermis. These rhabdomyoblast-like polygonal cells diffusely expressed desmin and were focally positive for MyoD1. Some clusters of polygonal cells in the deep dermis expressed SOX10. Collectively, these clinical and histopathologic features suggested MM with rhabdomyosarcomatous differentiation. Desmin- and skeletal-muscle-specific markers should be applied to melanocytic tumors with atypical epithelioid cells resembling rhabdomyoblasts, especially if these cells are negative for melanocytic markers.

Case Report: Phenotypic Switch in High-Grade B-Cell Lymphoma With MYC and BCL6 Rearrangements: A Potential Mechanism of Therapeutic Resistance in Lymphoma?

Lineage switch between myeloid and lymphoid in acute leukemia is well established as a mechanism for leukemic cells to escape chemotherapy. Cross-lineage transformation is also recognized in some solid tumors on targeted therapy, such as adenocarcinomas of the lung and prostate that transforms to neuroendocrine carcinoma on targeted therapy. Now lineage plasticity is increasingly recognized in mature lymphomas, such as small B-cell lymphomas transforming to histiocytic/dendritic cell sarcoma. However, there is no report of aggressive mature B-cell lymphoma switching from one histologic category to another upon targeted therapy. We report here a case of high-grade B-cell lymphoma with MYC and BCL6 rearrangements relapsing as a high-grade plasmablastic neoplasm with MYC and BCL6 rearrangements after R-CHOP and R-EPOCH therapy. Being aware of this rare scenario will help improve our understanding of the underlying mechanisms of therapeutic resistance and progression of lymphoma.

Spindle Cell Tumors of the Pleura and the Peritoneum: Pathologic Diagnosis and Updates

A diverse group of both benign and malignant spindle cell tumors can involve the pleura or the peritoneum. Due to their rarity and overlapping morphologic features, these tumors can pose considerable diagnostic difficulty in surgical pathology. As these tumors differ in their prognosis and clinical management, their correct pathologic diagnosis is critical. In addition to histologic assessment, select immunohistochemical and molecular tools can aid the distinction among these tumors. In this review, we consider some of the major histologic differential diagnosis of spindle cell tumors involving these serosal membranes. This list of tumors includes: solitary fibrous tumor, inflammatory myofibroblastic tumor, desmoid fibromatosis, synovial sarcoma, sarcomatoid carcinoma, spindle cell melanoma, dedifferentiated liposarcoma, epithelioid hemangioendothelioma, and sarcomatoid mesothelioma. We describe their salient clinicopathologic and genetic findings, with a review on some of the recent discoveries on their molecular pathogenesis.