[ALK rearranged Spitz melanocytoma: a clinicopathological and molecular genetic analysis of two cases].

Objective: To investigate the clinicopathological, immunohistochemical and molecular characteristics of cutaneous ALK-rearranged Spitz melanocytoma. Methods: Two cases of cutaneous ALK-rearranged Spitz melanocytoma from outside hospital consultations in Department of Pathology, Affiliated Cancer Hospital of Fudan University in August 2020 and in Shanghai Ackermann Medical Laboratory in June 2022 were collected. The clinicopathological features, immunophenotypes and molecular profiles of two patients with cutaneous Spitzoid melanocytic tumor harboring ALK-rearrangement were analyzed. The literatures were reviewed. Results: The study included an 8-year-old boy and an 11-year-old girl, who presented with a polypoid lesion in the skin of right thigh and left auricle measuring 1.0 cm and 1.2 cm, respectively. Histologically, they were composed of medium to large-sized epithelioid to plump spindle cells, arranged in nested, plexiform or fascicular patterns in the superficial dermis. The neoplastic cells had abundant eosinophilic cytoplasm with round to ovoid vesicular nuclei containing prominent eosinophilic nucleoli. One case showed mild to moderate nuclear pleomorphism and mitotic activity (average, 2/mm2). Immunohistochemically, the epithelioid and plump spindle cells showed diffuse and strong staining of S-100 protein, SOX10, and ALK (D5F3 and 1A4), but did not express HMB45, PNL2 and MiTF. ALK-rearrangement was detected by fuorescence in situ hybridization in both cases. Subsequent next generation sequence (NGS) analysis identified KANK1::ALK and TPM3:ALK fusions. At 34 and 14 months after surgical resection, both patients remained well with no signs of recurrence or metastasis. Conclusions: ALK-rearranged Spitz melanocytoma represents a morphologically and genetically distinct subset of Spitz melanocytoma, characterized clinically by predilection in children and adolescents, with Spitzoid morphology in plexiform pattern, positive immunohistochemical stains, and rearrangement of ALK. As some cases show atypical features and high mitotic activity, a distinction from Spitz melanoma is warranted.

Clinical, Morphological and Molecular Features of Spitz tumors.

Spitz tumors represent a heterogeneous group of challenging melanocytic neoplasms, displaying a range of biological behaviors, spanning from benign lesions, Spitz nevi (SN) to Spitz melanomas (SM), with intermediate lesions in between known as atypical Spitz tumors (AST). They are histologically characterized by large epithelioid and/or spindled melanocytes arranged in fascicles or nests, often associated with characteristic epidermal hyperplasia and fibrovascular stromal changes. In the last decade, the detection of mutually exclusive structural rearrangements involving receptor tyrosine kinases ROS1, ALK, NTRK1, NTRK2, NTRK3, RET, MET, serine threonine kinases BRAF and MAP3K8, or HRAS mutation, led to a clinical, morphological and molecular based classification of Spitz tumors. The recognition of some reproducible histological features can help dermatopathologist in assessing these lesions and can provide clues to predict the underlying molecular driver. In this review, we will focus on clinical and morphological findings in molecular Spitz tumor subgroups.

Histological interpretation of spitzoid tumours: an extensive machine learning-based concordance analysis for improving decision making.

The histopathological classification of melanocytic tumours with spitzoid features remains a challenging task. We confront the complexities involved in the histological classification of these tumours by proposing machine learning (ML) algorithms that objectively categorise the most relevant features in order of importance. The data set comprises 122 tumours (39 benign, 44 atypical and 39 malignant) from four different countries. BRAF and NRAS mutation status was evaluated in 51. Analysis of variance score was performed to rank 22 clinicopathological variables. The Gaussian naive Bayes algorithm achieved in distinguishing Spitz naevus from malignant spitzoid tumours with an accuracy of 0.95 and kappa score of 0.87, utilising the 12 most important variables. For benign versus non-benign Spitz tumours, the test reached a kappa score of 0.88 using the 13 highest-scored features. Furthermore, for the atypical Spitz tumours (AST) versus Spitz melanoma comparison, the logistic regression algorithm achieved a kappa value of 0.66 and an accuracy rate of 0.85. When the three categories were compared most AST were classified as melanoma, because of the similarities on histological features between the two groups. Our results show promise in supporting the histological classification of these tumours in clinical practice, and provide valuable insight into the use of ML to improve the accuracy and objectivity of this process while minimising interobserver variability. These proposed algorithms represent a potential solution to the lack of a clear threshold for the Spitz/spitzoid tumour classification, and its high accuracy supports its usefulness as a helpful tool to improve diagnostic decision-making.

Spitz tumour with ALK rearrangement: A case report and literature review.

Spitz tumour with ALK rearrangement is a recently described entity and a rare tumour. The incidence of Spitz tumour was estimated at 3.63 per 100,000 persons in American paediatric population; while there is no data in Asian population. Here we reported a case of an eleven-year-old Asian boy who presented with a left shin nodule of two months' duration. The skin biopsy revealed a Spitz tumour with predominantly spindle cell morphology arranged in fascicles, vertically orientated nests and radial growth pattern. Junctional component, melanin pigment or Kamino bodies were not identified. Immunohistochemical study displayed homogenous cytoplasmic staining for ALK. Fluorescence in-situ hybridisation (FISH) analysis confirmed ALK rearrangement. Review of the literatures demonstrated that positive ALK immunohistochemistry may not correlate with ALK rearrangement. ALK-rearranged Spitz tumour confirmed with FISH analysis favour clinically benign behaviour despite atypical histomorphology or positive sentinel lymph node. Therefore, correlation of histomorphology, immunohistochemical stain and molecular study are important for the definitive diagnosis of this entity.

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.

Spitz melanocytic neoplasms with MLPH::ALK fusions: Report of two cases with previously unreported features and literature review.

ALK-fused Spitz melanocytic neoplasms are a distinct subgroup of melanocytic lesions exhibiting unique histopathologic characteristics. These lesions often manifest as exophytic or polypoid tumors, characterized by fusiform-to-epithelioid melanocytes arranged in a nested, fascicular, or plexiform growth pattern. Several fusion partners of the ALK gene have been identified in spitzoid melanocytic neoplasms, with TPM3 and DCTN1 being the most prevalent. Less common fusion partners include NPM1, TPR, CLIP1, GTF3C2, EEF2, MYO5A, KANK1, and EHBP1. The MLPH gene, which encodes melanophilin (MLPH), playing a crucial role in regulating skin pigmentation by acting as a linker between RAB27A and myosin Va during melanosome transport, has also recently been recognized as a rare fusion partner of ALK in Spitz melanocytic neoplasms. Currently, there exists a sparse documentation within English literature, illustrating a limited number of cases featuring MLPH::ALK fusion in Spitz melanocytic neoplasms. In this report, we present two additional cases, including a previously unreported instance of Spitz melanoma, contributing to the expanding knowledge on ALK-fused Spitz melanocytic neoplasms. In addition, we provide a comprehensive review of the clinical, histopathologic, and molecular features observed in documented cases with this novel fusion.

Amplification of Mutant NRAS in Melanocytic Tumors With Features of Spitz Tumors.

NRAS activating mutations are prevalent in melanocytic neoplasia, occurring in a subset of common acquired melanocytic nevi and ∼30% of cutaneous melanomas. In this study, we described a cohort of 7 distinctive melanocytic tumors characterized by activating point mutations in codon 61 of NRAS with amplification of the mutant NRAS allele and shared clinicopathologic features. These tumors occurred predominantly in younger patients, with a median age of 20 years (range, 6-56 years). They presented as papules on the helix of the ear (4 cases) or extremities (3 cases). Microscopically, the tumors were cellular, relatively well-circumscribed, compound, or intradermal proliferations. The tumor cells often extended into the deep reticular dermis and involved the superficial subcutaneous fat in some cases. The melanocytes were epithelioid to spindled with moderate amounts of cytoplasm and conspicuous nucleoli. They were arranged in short plexiform fascicles, nests, and cords. Some cases had occasional pleomorphic and multinucleated melanocytes. Rare dermal mitotic figures were present in all cases. The dermis contained thick collagen bundles and minimal solar elastosis. Follow-up data were available for 5 patients, with a median period of 4.2 years (range, 1-9 years), during which no recurrences or metastases were reported. Our series highlights a clinicopathologically and molecularly distinctive subset of NRAS-mutated tumors with amplification of the mutant NRAS allele.

Restrospective reappraisal of the prognostic classification of spitzoid melanocytic neoplasms after BRAF and NRAS mutation characterisation: a single institution experience.

AIMS: The current WHO classification of melanocytic tumours excludes neoplasms showing BRAF or NRAS mutations from the Spitz category. This study aimed to review and reclassify atypical melanocytic tumours with spitzoid morphological features diagnosed between 2009 and 2021 in our hospital after expanding the molecular profile, including BRAF and NRAS mutations in all cases. METHODS AND RESULTS: A total of 71 neoplasms showing spitzoid features (Spitz-like) and atypia were included. The risk of progression of tumours was first studied by integrating the morphology, immunohistochemistry (p16, Ki67, HMB45 and PRAME) and fluorescence in-situ hybridisation (FISH) results (melanoma multiprobe and 9p21). In a second step, after expanding the molecular study, including BRAF and NRAS mutational status, the neoplasms were finally classified into four subgroups: atypical Spitz tumour (AST, n = 45); BRAF-mutated naevus/low-grade melanocytoma with spitzoid morphology (BAMS, n = 2); Spitz melanoma (SM, n = 14); and BRAF or NRAS mutated melanoma with spitzoid features (MSF, n = 10). Follow-up of patients revealed uneventful results for AST and BAMS. Only one SM presented lymph node metastasis after 134 months. Conversely, patients with MSF showed an unfavourable outcome: three developed lymph node metastases after a mean time of 22 months, with one patient presenting distant metastasis and dying of the disease 64 months from diagnosis. The progression-free survival showed significant differences between the four groups of spitzoid tumours (P < 0.001) and between both melanoma subtypes (P = 0.012). CONCLUSIONS: The classification and prognostication of atypical neoplasms with spitzoid features requires the integration of histomorphology with the molecular investigation of tumours, which should include BRAF and NRAS mutational status.

Assessment of RAS-RAF-MAPK Pathway Mutation Status in Healthy Skin, Benign Nevi, and Cutaneous Melanomas: Pilot Study Using Droplet Digital PCR.

In the present study, we employed the ddPCR and IHC techniques to assess the prevalence and roles of RAS and RAF mutations in a small batch of melanoma (n = 22), benign moles (n = 15), and normal skin samples (n = 15). Mutational screening revealed the coexistence of BRAF and NRAS mutations in melanomas and nevi and the occurrence of NRAS G12/G13 variants in healthy skin. All investigated nevi had driver mutations in the BRAF or NRAS genes and elevated p16 protein expression, indicating cell cycle arrest despite an increased mutational burden. BRAF V600 mutations were identified in 54% of melanomas, and NRAS G12/G13 mutations in 50%. The BRAF mutations were associated with the Breslow index (BI) (p = 0.029) and TIL infiltration (p = 0.027), whereas the NRAS mutations correlated with the BI (p = 0.01) and the mitotic index (p = 0.04). Here, we demonstrate that the "young" ddPCR technology is as effective as a CE-IVD marked real-time PCR method for detecting BRAF V600 hotspot mutations in tumor biopsies and recommend it for extended use in clinical settings. Moreover, ddPCR was able to detect low-frequency hotspot mutations, such as NRAS G12/G13, in our tissue specimens, which makes it a promising tool for investigating the mutational landscape of sun-damaged skin, benign nevi, and melanomas in more extensive clinical studies.

Spitz Melanocytic Tumors: A Fascinating 75-Year Journey.

Over the last 75 years, our understanding of Spitz lesions has undergone substantial evolution. Initially considered a specific type of melanoma, the perception has shifted towards recognizing Spitz lesions as a spectrum comprising Spitz nevi, Spitz melanocytomas, and Spitz melanomas. Spitz lesions are known for posing a significant diagnostic challenge regarding the distinction between benign neoplasms displaying atypical traits and melanomas. A comprehensive understanding of their molecular basis and genomic aberrations has significantly improved precision in classifying and diagnosing these challenging lesions. The primary aim of this review is to encapsulate the current understanding of the molecular pathogenesis and distinct clinicopathologic characteristics defining this intriguing set of tumors.

Clinical, Morphologic, and Molecular Features of MAP3K8 Rearranged Spitz Neoplasms: A Retrospective Study Documenting That Bonafide Spitz Melanomas Are Rare.

Previous studies regarding the clinical behavior of Spitz neoplasms lack genomic characterization. We aim to assess our hypothesis that most MAP3K8 Spitz neoplasms are indolent despite MAP3K8 being the single most common driver of Spitz melanoma. Further, we aim to identify genomic features associated with aggressive behavior and to better characterize the morphology of these cases. We analyzed the outcomes of MAP3K8 Spitz neoplasms. We also performed a meta-analysis of the outcomes of MAP3K8 Spitz from the literature. Morphologic features were compared with other variants of Spitz using a Student t test and χ 2 test. Two of 35 cases resulted in local recurrence and one of these cases had local regional metastasis; all other cases had no evidence of recurrence (mean follow-up time: 33 mo). MAP3K8 Spitz only rarely results in aggressive behavior. Metastatic cases have genomic mutations associated with tumor progression. Morphologically, MAP3K8 Spitz neoplasms frequently showed nodular silhouette, large cell size, epithelioid morphology, and severe nuclear atypia resulting in more frequent diagnosis as Spitz melanoma. Most MAP3K8 Spitz neoplasms have excellent prognoses, apart from rare cases harboring additional genomic abnormalities associated with tumor progression.