Genomic analysis of a case of agminated Spitz nevi and congenital-pattern nevi arising in extensive nevus spilus

Diagnostic Imaging of Agminated Blue Lesions and Blue Lesions with Satellitosis: Case Series with a Concise Review of the Current Literature

Background: Agmination and/or satellitosis in pigmented blue lesions is a phenomenon rarely mentioned in the literature and not well known. This phenomenon can be expressed by several benign and malignant pigmented blue lesions, such as blue nevi, Spitz nevi, melanocytoma and melanoma. On this spectrum, dermoscopy, reflectance confocal microscopy (RCM) and dynamic Optical coherence tomography (D-OCT) represent non-invasive imaging technologies, which may help clinicians in the diagnosis of melanoma and non-melanoma skin cancers in daily clinical practice. Methods: Currently, in the literature there is a lack of new data about agminated blue lesions and blues lesions with satellitosis, as well as the lack of a recent and updated review of the literature about this topic. Therefore, considering that clinicians must be confident with the diagnosis of these rare skin lesions, we decided to carry out this work. Results: In this paper, four new cases of agminated pigmented cutaneous lesions were described. Moreover, a review of the current literature on this topic was performed. Conclusions: A clinical-pathological correlation is often needed to reach a correct diagnosis; currently, dermoscopy and non-invasive diagnostic techniques, such as reflectance confocal microscopy and optical coherence tomography, due to the depth of these skin lesions in the dermis, can only make a partial and limited contribution.

Melanoma in infants, caused by a gene fusion involving the anaplastic lymphoma kinase (ALK)

We describe the first cases of pediatric melanoma with ALK fusion gene arising within giant congenital melanocytic nevi. Two newborn boys presented with large pigmented nodular plaques and numerous smaller satellite nevi. Additional expansile nodules developed within both nevi and invasive melanomas were diagnosed before 10 months of age in both boys. Oncogenic driver mutations in NRAS and BRAF were absent in both cases. Instead, oncogenic ZEB2::ALK fusion genes were identified in both the nevus and melanoma developing within the nevus. In both cases, tumors were noted by ultrasound in utero, demonstrated significant nodularity at birth, and progressed to melanoma in the first year of life suggesting that congenital nevi with ALK fusion genes may behave more aggressively than those with other mutations. As ALK kinase inhibitors are effective against a range of tumors with similar ALK fusion kinases, identifying ALK fusion genes in congenital melanocytic nevi may provide an opportunity for targeted therapy.

Agminated presentation of fusion-driven melanocytic neoplasms

BACKGROUND

The conventionally understood pathogenesis of agminated Spitz nevi includes a mosaic HRAS mutation followed by copy number gains in 11p. However, we have recently observed agminated presentations of fusion-driven melanocytic neoplasms.

METHODS

We retrieved cases from our database of benign fusion-induced melanocytic neoplasms with an agminated presentation. Both the primary lesion and the secondary lesion were sequenced. TERT-promoter mutational testing and the melanoma fluorescence in situ hybridization assay were also performed.

RESULTS

Three cases were included. Two had a PRKCA fusion (partners ATP2B4 and MPZL1) and one had a ZCCHC8::ROS1 fusion. None of the cases met morphologic or molecular criteria for malignancy. There was no evidence of tumor progression in secondary lesions. The same fusion was identified in the primary and secondary lesions. None of the patients developed evidence of nodal or systemic metastasis.

CONCLUSIONS

We present accumulating evidence that fusion-driven melanocytic neoplasms can present with an agminated presentation. The differential diagnosis of an agminated presentation versus a locally recurrent or potentially locally metastatic tumor is critical, and accurate diagnosis has significant prognostic and therapeutic consequences for the patient. As with HRAS mutations, fusion-driven melanocytic tumors may have an agminated presentation.

An update on genomic aberrations in Spitz naevi and tumours

Spitz neoplasms continue to be a diagnostic challenge for dermatopathologists and are defined by distinctive morphological and genetic features. With the recent advancements in genomic sequencing, the classification, diagnosis, and prognostication of these tumours have greatly improved. Several subtypes of Spitz neoplasms have been identified based on their specific genomic aberrations, which often correlate with distinctive morphologies and biological behaviour. These genetic driver events can be classified into four major groups, including: (1) mutations [HRAS mutations (with or without 11p amplification) and 6q23 deletions]; (2) tyrosine kinase fusions (ROS1, ALK, NTRK1-3, MET and RET); (3) serine/threonine kinase fusions and mutations (BRAF, MAP3K8, and MAP2K1); and (4) other rare genomic aberrations. These driver genomic events are hypothesised to enable the initial proliferation of melanocytes and are often accompanied by additional genomic aberrations that affect biological behaviour. The discovery of theses genomic fusions has allowed for a more objective definition of a Spitz neoplasm. Further studies have shown that the majority of morphologically Spitzoid appearing melanocytic neoplasms with aggressive behaviour are in fact BRAF or NRAS mutated tumours mimicking Spitz. Truly malignant fusion driven Spitz neoplasms may occur but are relatively uncommon, and biomarkers such as homozygous 9p21 (CDKN2A) deletions or TERT-p mutations can have some prognostic value in such cases. In this review, we discuss the importance and various methods of identifying Spitz associated genomic fusions to help provide more definitive classification. We also discuss characteristic features of the various fusion subtypes as well as prognostic biomarkers.

The Morpho-Molecular Landscape of Spitz Neoplasms

Spitz neoplasms are a heterogeneous group of melanocytic proliferations with a great variability in the histological characteristics and in the biological behavior. Thanks to recent discoveries, the morpho-molecular landscape of Spitz lineage is becoming clearer, with the identification of subtypes with recurrent features thus providing the basis for a more solid and precise tumor classification. Indeed, specific mutually exclusive driver molecular events, namely HRAS or MAP2K1 mutations, copy number gains of 11p, and fusions involving ALK, ROS, NTRK1, NTRK2, NTRK3, MET, RET, MAP3K8, and BRAF genes, correlate with distinctive histological features. The accumulation of further molecular aberrations, instead, promotes the increasing malignant transformation of Spitz neoplasms. Thus, the detection of a driver genetic alteration can be achieved using the appropriate diagnostic tests chosen according to the histological characteristics of the lesion. This allows the recognition of subtypes with aggressive behavior requiring further molecular investigations. This review provides an update on the morpho-molecular correlations in Spitz neoplasms.

GOPC-ROS1 mosaicism in agminated Spitz naevi: report of two cases

Spitz tumors are genetically associated with activating HRAS point mutations or fusions of either ALK, ROS1, NTRK1, NTRK3, RET, MET, MERTK, LCK, BRAF, MAP3K8, or MAP3K3. All these driver gene alterations are mutually exclusive. We report two cases of agminated Spitz naevi with a GOPC-ROS1 fusion. Both cases occurred on the lower limb of young adults. Since adolescence, pigmented or pink-colored papules have been periodically arising in a limited area of skin. In one case, an ill-defined hyperpigmented macule known since childhood was present in the background. Morphologically, at least five lesions were analyzed from each patient. In one case, all were predominantly junctional pigmented Spitz naevi, and in the other case, all were compound unpigmented Spitz naevi. No atypical features were present. RNA-sequencing revealed a GOPC-ROS1 gene translocation in both cases. Split signals of ROS1 gene in fluorescence in situ hybridization were observed not only in the nests of spitzoid melanocytes but also in the bland basal melanocytes surrounding the proliferations. These findings suggest the presence of a GOPC-ROS1 mosaicism in melanocytes with further emergence of agminated Spitz naevi potentially triggered by other genetic alterations. This expands the spectrum of genetic anomalies described in agminated Spitz naevi and our understanding of the mechanisms involved in their emergence.

Novel three-way complex rearrangement of TRPM1-PUM1-LCK in a case of agminated Spitz nevi arising in a giant congenital hyperpigmented macule

The genetic anomalies associated with the agminated variant of Spitz nevus have so far been limited to HRAS G13R mutations, especially when arising within a nevus spilus. A previous report exposed the case of a man with a giant pigmented macule involving his upper right limb and trunk. Since childhood, Spitz nevi have been periodically arising, within the pigmented area. The histopathology of several lesions displayed the usual criteria of junctional, compound, or intradermal Spitz nevi with a diversity of cytomorphological and architectural features. Some lesions spontaneously regressed. Genetic studies confirmed in three lesions an identical translocation involving TRPM1, PUM1, and LCK. No mutations in HRAS, NRAS, BRAF, or other known fusion genes linked to Spitz nevus were detected. LCK break-apart fluorescence in situ hybridization confirmed the rearrangement was present not only in the melanocytic proliferation but also in the surrounding non-spitzoid melanocytes. This report expands the list of genetic alterations involved both in giant congenital macules and in agminated Spitz nevi, and also extends the concept of mosaicism in melanocytes to gene translocations.