Clinical, Morphologic, and Molecular Features of Benign and Intermediate-grade Melanocytic Tumors With Activating Mutations in MAP2K1

Clinical outcomes and genomic profiles of MAP2K1-mutated primary cutaneous melanocytic tumours

BACKGROUND

Primary cutaneous melanocytic tumours harbouring MAP2K1 mutations without second-hit genomic alterations represent a subclass of neoplasms with poorly understood biological behaviour. This study aimed to investigate the clinical outcomes and genomic characteristics of these tumours.

METHODS

This cohort study included primary cutaneous melanocytic tumours with MAP2K1 mutations from patients at two academic centres (Leiden University Medical Centre and University Medical Centre Utrecht). These mutations were categorised into three functional classes: Class I (RAF-dependent), Class II (RAF-regulated), and Class III (RAF-independent). Tumours underwent histopathological evaluation, next-generation sequencing (NGS), and copy number variation (CNV) analysis and were categorised as non-melanoma or melanoma. Clinical outcomes were assessed for each mutation class during follow-up visits and through the Dutch Pathology Database (PALGA) using the composite outcome of metastatic melanoma (recurrence, metastasis, or melanoma-related death).

FINDINGS

A total of 102 patients were included, with tumours classified as melanoma in 52 (51%) and non-melanoma in 50 (49%). The tumours displayed spitzoid histomorphology in over two-thirds of cases and harboured 31 distinct MAP2K1 mutations: 20 Class I (19.6%), 56 Class II (54.9%), and 26 Class III (25.5%). Class I mutations exclusively co-occurred with BRAF or NRAS mutations, while Class II and III mutations often acted as sole tumour drivers. Of the tumours with Class I mutations, 95% were classified as melanoma, which was less frequently the case for Class II (risk ratio [RR] 0.43 [95% CI: 0.31-0.60], p < 0.001) and Class III mutations (RR 0.40 [95% CI: 0.25-0.67], p < 0.001). MAP2K1 mutation Class and TERT-p mutation status were independent predictors for the composite outcome. Compared to Class I mutations, Class II mutations were negatively associated with the composite outcome (odds ratio [OR] 0.16 [95% CI: 0.03-0.75], p = 0.03), whereas Class III mutations were not associated (OR 0.31 [95% CI: 0.05-1.54], p = 0.16). TERT-p mutations were positively associated with the composite outcome (OR 23.1, 95% CI: 3.99-439.8, p < 0.005).

INTERPRETATION

Class I MAP2K1 mutations typically occur alongside other MAPK pathway mutations and may contribute to aggressive melanoma behaviour. In contrast, Class II and III MAP2K1 mutations can independently drive melanocytic tumourigenesis with a potential for metastasis, aligning with conventional melanomagenesis pathways, despite their frequent spitzoid histomorphology.

FUNDING

This research was supported by the Hanarth Fund.

Role of Targeted Sequencing in Routine Diagnostics of Spitz Melanocytic Neoplasms-An Analysis of 70 Cases

BACKGROUND

There is growing evidence that the Spitz group of melanocytic neoplasms should be restricted to those harboring kinase receptor fusions and HRAS mutations/11p15 amplification. The presence of genomic alterations characteristic of conventional melanomas (BRAF and NRAS mutations) precludes a diagnosis of a Spitz neoplasm. It is often challenging to distinguish Spitz neoplasms from conventional melanomas with spitzoid morphology on histopathological grounds alone.

METHODS

We report a series of 70 consecutive melanocytic tumors in which targeted sequencing was indicated to distinguish Spitz from spitzoid neoplasms and to classify Spitz neoplasms along the biological spectrum.

RESULTS

Final diagnoses incorporating molecular results included 12 conventional melanomas (nine of which with NRAS mutations), five Spitz melanomas, 35 atypical Spitz tumors, eight Spitz nevi, three melanocytic tumors with a MAP2K1 mutation, and seven desmoplastic Spitz nevi/tumors. There were significant discrepancies between initial diagnoses and final diagnoses after incorporating molecular results in 24 (34%) cases, including nine conventional melanomas favored to be Spitz neoplasms and nine Spitz neoplasms favored to be conventional melanomas.

CONCLUSIONS

It is often not possible to reliably distinguish Spitz neoplasms from spitzoid melanocytic tumors without identifying their driver genomic alterations. Applying next-generation sequencing in diagnostically problematic tumors improves diagnostic accuracy.

Gene Expression Profile of Benign, Intermediate, and Malignant Spitz and Spitzoid Melanocytic Lesions

Spitz and Spitzoid lesions represent one of the most challenging melanocytic neoplasms in dermatopathology. Nosologic classification has been more recently improved by the discovery of novel molecular drivers, particularly translocations. In the current study, we aimed to use an unbiased approach to explore the gene expression profile of a group of melanocytic Spitz and Spitzoid melanocytic lesions ranging from benign lesions to melanoma, including intermediate lesions such as SPARK nevi and atypical Spitz tumors/melanocytomas. Using unsupervised analysis of gene expression data, we found some distinct hierarchical clusters of lesions, including groups characterized by ALK and NTRK translocations. Few non-ALK translocated tumors demonstrated increased ALK expression, confirmed by immunohistochemistry. Spitz tumors with overlapping features of dysplastic nevi, so-called SPARK nevi, appear to have a common gene expression profile by hierarchical clustering. Finally, weighted gene correlation network analysis identified gene modules variably regulated in subtypes of these cases. Thus, gene expression profiling of Spitz and Spitzoid lesions represents a viable instrument for the characterization of these lesions.

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.

Spitz Tumors and Melanoma in the Genomic Age: A Retrospective Look at Ackerman's Conundrum

After 25 years, "Ackerman's conundrum", namely, the distinction of benign from malignant Spitz neoplasms, remains challenging. Genomic studies have shown that most Spitz tumors harbor tyrosine and serine/threonine kinase fusions, including ALK, ROS1, NTRK1, NTRK2, NTRK3, BRAF and MAP3K8, or some mutations, such as HRAS and MAP3K8. These chromosomal abnormalities act as drivers, initiating the oncogenetic process and conferring basic bio-morphological features. Most Spitz tumors show no additional genomic alterations or few ones; others harbor a variable number of mutations, capable of conferring characteristics related to clinical behavior, including CDKN2A deletion and TERT-p mutation. Since the accumulation of mutations is gradual and progressive, tumors appear to form a bio-morphologic spectrum, in which they show a progressive increase of clinical risk and histological atypia. In this context, a binary classification Spitz nevus-melanoma appears as no longer adequate, not corresponding to the real genomic substrate of lesions. A ternary classification Spitz nevus-Spitz melanocytoma-Spitz melanoma is more adherent to the real neoplastic pathway, but some cases with intermediate ambiguous features remain difficult to diagnose. A prognostic stratification of Spitz tumors, based on the morphologic and genomic characteristics, as a complement to the diagnosis, may contribute to better treatment plans for patients.