Multiple Congenital Melanocytic Naevi Research Articles

Mosaic BRAF Fusions Are a Recurrent Cause of Congenital Melanocytic Nevi Targetable by MAPK Pathway Inhibition

Among children with multiple congenital melanocytic naevi (CMN), 25% have no established genetic cause, of which many develop a hyperproliferative and severely pruritic phenotype resistant to treatment. Gene fusions have been reported in individual cases of CMN. Here, we study 169 CMN patients, 38 of whom were double wild-type for NRAS/BRAF mutations. Nineteen of these 38 patients had sufficient tissue to undergo RNAseq, which revealed mosaic BRAF fusions in 11/19 patients and mosaic RAF1 fusions in 1/19. Recurrently, fusions involved the loss of the 5' regulatory domain of BRAF or RAF1 but preserved the kinase domain. We validated all cases and detected the fusions in two separate naevi in 5/12 patients, confirming clonality. The absence of the fusion in blood in 8/12 patients indicated mosaicism. Primary culture of BRAF-fusion naevus cells from 3/12 patients demonstrated highly increased MAPK activation, despite only mildly increased BRAF expression, suggesting additional mechanisms of kinase activation. Trametinib quenched MAPK hyperactivation in vitro and treatment of two patients caused rapid improvement in bulk tissue, improving bodily movement, and reducing inflammation and severe pruritus. These findings offer a genetic diagnosis to an additional group of patients and trametinib as a treatment option for the severe associated phenotypes.

260 Mosaic BRAF fusions are a recurrent cause of multiple congenital melanocytic naevi

Congenital melanocytic naevi (CMN) are moles present at birth, and when multiple or very extensive can involve other organ systems as well as predisposing to melanoma. Some CMN develop a highly proliferative phenotype whose progression is poorly understood. Genotypically, CMN are caused by mosaic NRAS missense mutations in 67% of cases and BRAF missense mutations in 7% of cases. Single cases of mosaic gene fusions have been previously described. To investigate the remaining 25%, skin biopsies from 19 patients shown to be double wildtype for NRAS/BRAF underwent transcriptome-wide paired-end RNA sequencing to detect gene fusion transcripts.

Abstract 2014: Mosaic BRAF fusions are a recurrent cause of multiple congenital melanocytic naevi

Abstract Congenital melanocytic naevi (CMN) are moles present at birth, and when multiple or very extensive can involve other organ systems as well as predisposing to melanoma. Some CMN patients develop a highly proliferative multinodular phenotype leading to chronic intense pruritus, and the causes for that specific phenotype progression are poorly understood. Genotypically CMN are mosaic single gene disorders. Thus far only two recurrent variants have been described as clearly causative: NRAS missense variants affecting codon 61 accounting for 68% of cases, and BRAF missense variants affecting codon 600 accounting for 7% of cases. Small numbers of cases of CMN have been reported to carry gene-fusions, and in 2 cases in the world literature (one BRAF-fusion and one RAF1-fusion) these have been shown to be clonal and therefore likely causal. We sought to address the issue of causation of the remaining 25%. From an initial large cohort study, skin biopsies from 19 patients were shown to be double wildtype for NRAS/BRAF and had sufficient tissue for further study after deep whole exome sequencing. These 19 samples then underwent transcriptome-wide paired-end RNA sequencing with bioinformatics analysis (STAR-Fusion v1.6 and Fusion Inspector v2.3) for gene fusion transcripts. 11/19 patients were found to have BRAFgene fusions, of which 7 had the multinodular proliferative phenotype. Fusions were confirmed on Sanger sequencing of the cDNA across the fusion junction, specifically demonstrated in 8 children from more than one separate skin lesion, confirming clonality. In the fusions identified, BRAF was fused to 11 different partner genes (GOLGA4, QKI, STRN3, AGAP3, MKRN2, PHIP, LCA5, EEA1, AKAP9, SEC31A, MIER3). This resulted in loss of the 5’ regulatory domain of BRAF but preservation of the kinase domain, such that expression was driven by the 5’ fusion partner. This structure follows the pattern of somatic BRAF-fusions reported previously in solid tumors including melanoma. Potential dimerization domains in the partner genes were identified in 9 cases. We identify here mosaic BRAF fusions as a recurrent cause of multiple CMN allowing genetic diagnosis in a further 15% of cases and linking this genotype to a highly proliferative pruritic phenotype. In vitro data from melanoma cell lines have suggested that higher expression levels of the fusion protein as well as dimerization domains in the partner gene correlate with resistance and/or paradoxical MAP-kinase activation after treatment with RAF and MEK inhibitors. This may have implications for the use of targeted therapies for attempted reduction of the nodular phenotype, or where melanoma arises in CMN patients caused by mosaic BRAF-fusions. Citation Format: Sara Barberan Martin, Satyamaanasa Polubothu, Alicia Bruzos, Neil Bulstrode, Gavin Kelly, Veronica Kinsler. Mosaic BRAF fusions are a recurrent cause of multiple congenital melanocytic naevi [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2014.

RF02: Mosaic BRAF fusions are a recurrent cause of multiple congenital melanocytic naevi

RF02: Mosaic <i>BRAF</i> fusions are a recurrent cause of multiple congenital melanocytic naevi

Does the gene matter? Genotype-phenotype and genotype-outcome associations in congenital melanocytic naevi.

SummaryBackgroundGenotype–phenotype studies can identify subgroups of patients with specific clinical features or differing outcomes, which can help shape management.ObjectivesTo characterize the frequency of different causative genotypes in congenital melanocytic naevi (CMN), and to investigate genotype–phenotype and genotype–outcome associations.MethodsWe conducted a large cohort study in which we undertook MC1R genotyping from blood, and high‐sensitivity genotyping of NRAS and BRAF hotspots in 156 naevus biopsies from 134 patients with CMN [male 40%; multiple CMN 76%; projected adult size (PAS) > 20 cm, 59%].ResultsMosaic NRAS mutations were detected in 68%, mutually exclusive with BRAF mutations in 7%, with double wild‐type in 25%. Two separate naevi were sequenced in five of seven patients with BRAF mutations, confirming clonality. Five of seven patients with BRAF mutations had a dramatic multinodular phenotype, with characteristic histology distinct from classical proliferative nodules. NRAS mutation was the commonest in all sizes of CMN, but was particularly common in naevi with PAS > 60 cm, implying more tolerance to that mutation early in embryogenesis. Facial features were less common in double wild‐type patients. Importantly, the incidence of congenital neurological disease, and apparently of melanoma, was not altered by genotype; no cases of melanoma were seen in BRAF‐mutant multiple CMN, however, this genotype is rare.Conclusions CMN of all sizes are most commonly caused by mutations in NRAS. BRAF is confirmed as a much rarer cause of multiple CMN, and appears to be commonly associated with a multinodular phenotype. Genotype in this cohort was not associated with differences in incidence of neurological disease in childhood. However, genotyping should be undertaken in suspected melanoma, for guidance of treatment. What's already known about this topic? Multiple congenital melanocytic naevi (CMN) have been shown to be caused by NRAS mosaic mutations in 70–80% of cases, by BRAF mosaicism in one case report and by inference in some previous cases.There has been debate about genotypic association with different sizes of CMN, and no data on genotype–outcome. What does this study add? NRAS mosaicism was found in 68%, BRAF in 7% and double wild‐type in 25% of cases of CMN. NRAS was the commonest mutation in all sizes of CMN, but was nearly universal in projected adult size > 60 cm. BRAF is often associated with a distinct multinodular clinical/histological phenotype.Adverse outcomes did not differ between genotypes on current numbers.

Growth and hormone profiling in children with congenital melanocytic naevi.

SummaryBackgroundMultiple congenital melanocytic naevi (CMN) is a rare mosaic RASopathy, caused by postzygotic activating mutations in NRAS. Growth and hormonal disturbances are described in germline RASopathies, but growth and hormone status have not previously been investigated in individuals with CMN.ObjectivesTo explore premature thelarche, undescended testes, and a clinically abnormal fat distribution with CMN through prospective endocrinological assessment of a cohort of subjects with CMN, and a retrospective review of longitudinal growth of a larger group of patients with CMN from outpatient clinics (which included all subjects in the endocrinological assessment group).Patients and methodsLongitudinal growth in a cohort of 202 patients with single or multiple CMN was compared with the U.K. National Child Measurement Programme 2010. Forty‐seven children had hormonal profiling including measurement of circulating luteinizing hormone, follicle‐stimulating hormone, thyroid stimulating hormone, adrenocorticotrophic hormone, growth hormone, prolactin, pro‐opiomelanocortin, estradiol, testosterone, cortisol, thyroxine, insulin‐like growth factor‐1 and leptin; 10 had oral glucose tolerance testing 25 had dual‐energy X‐ray absorptiometry scans for body composition.ResultsBody mass index increased markedly with age (coefficient 0·119, SE 0·016 standard deviation scores per year), at twice the rate of the U.K. population, due to increased adiposity. Three per cent of girls had premature thelarche variant and 6% of boys had persistent undescended testes. Both fat and muscle mass were reduced in areas underlying large naevi, resulting in limb asymmetry and abnormal truncal fat distribution. Anterior pituitary hormone profiling revealed subtle and variable abnormalities. Oral glucose tolerance tests revealed moderate–severe insulin insensitivity in five of 10, and impaired glucose tolerance in one.ConclusionsInterpersonal variation may reflect the mosaic nature of this disease and patients should be considered individually. Postnatal weight gain is potentially related to the underlying genetic defect; however, environmental reasons cannot be excluded. Naevus‐related reduction of fat and muscle mass suggests local hormonal or metabolic effects on development or growth of adjacent tissues, or mosaic involvement of these tissues at the genetic level. Premature thelarche and undescended testes should be looked for, and investigated, as for any child.

Classification of neurological abnormalities in children with congenital melanocytic naevus syndrome identifies magnetic resonance imaging as the best predictor of clinical outcome.

SummaryBackgroundThe spectrum of central nervous system (CNS) abnormalities described in association with congenital melanocytic naevi (CMN) includes congenital, acquired, melanotic and nonmelanotic pathology. Historically, symptomatic CNS abnormalities were considered to carry a poor prognosis, although studies from large centres have suggested a much wider variation in outcome.ObjectivesTo establish whether routine MRI of the CNS is a clinically relevant investigation in children with multiple CMN (more than one at birth), and to subclassify radiological abnormalities.MethodsOf 376 patients seen between 1991 and 2013, 289 fulfilled our criterion for a single screening CNS MRI, which since 2008 has been more than one CMN at birth, independent of size and site of the largest naevus. Cutaneous phenotyping and radiological variables were combined in a multiple regression model of long‐term outcome measures (abnormal neurodevelopment, seizures, requirement for neurosurgery).ResultsTwenty‐one per cent of children with multiple CMN had an abnormal MRI. Abnormal MRI was the most significant predictor of all outcome measures. Abnormalities were subclassified into group 1 ‘intraparenchymal melanosis alone’ (n = 28) and group 2 ‘all other pathology’ (n = 18). Group 1 was not associated with malignancy or death during the study period, even when symptomatic with seizures or developmental delay, whereas group 2 showed a much more complex picture, requiring individual assessment.ConclusionsFor screening for congenital neurological lesions a single MRI in multiple CMN is a clinically relevant strategy. Any child with a stepwise change in neurological/developmental symptoms or signs should have an MRI with contrast of the brain and spine to look for new CNS melanoma.

Immunohistochemical and ultrastructural features of congenital melanocytic naevus cells support a stem‐cell phenotype

Background Multiple congenital melanocytic naevi (CMN) in one individual are caused by somatic mosaicism for NRAS mutations; however, the lineage of the mutated cells remains uncertain.Objectives To test the hypothesis that CMN may be derived from cutaneous stem cells.Methods Sixty-six CMN samples from 44 patients were stained for immunohistochemical (IHC) markers of melanocytic differentiation (TYR, TRP1, TRP2, LEF1, MITF, cKit), pluripotency (nestin, fascin, CD133, CD20, CD34), monocyte/macrophage lineage (CD68, CD163, CD14), proliferation (Ki67) and MTOR/Wnt-signalling pathway activation (pS6, β-catenin). Semiquantitative scoring compared samples with naevus cell nesting (group 1) with those with only diffuse dermal infiltration (group 2). Transmission electron microscopy (TEM) was performed on 10 samples.Results A normal melanocyte population was seen overlying many dermal CMN. Group 1 samples were significantly more likely to express melanocytic differentiation markers than group 2, and expression decreased significantly with depth. Expression of these markers was correlated with each other, and with nestin and fascin. CD20 staining was positive in a substantial proportion and was stronger superficially. Expression of β-catenin and pS6 was almost universal. Some samples expressed monocyte/macrophage markers. TEM revealed variable naevus cell morphology, striking macromelanosomes, double cilia and microvilli.Conclusions Congenital melanocytic naevi development frequently coexists with normal overlying melanocyte development, leading us to hypothesize that in these cases CMN are likely to develop from a cell present in the skin independent of, or remaining after, normal melanocytic migration. IHC and TEM findings are compatible with CMN cells being of cutaneous stem-cell origin, capable of some degree of melanocytic differentiation superficially.

Giant Bathing Trunk Naevus with Multiple Congenital Melanocytic Naevi

Congenital nevi are hyperpigmented macular lesions that are derivatives of the melanoblasts. They occur in less than 1% of the neonates in any site of the body. The giant congenital nevus is greater than 20 cm in size, pigmented and often hairy. Between 4% and 6% of these lesions will develop into a malignant melanoma. Since approximately 50% of the melanomas develop by the age of two, and 80% by the age of seven, early removal is recommended. However, their large size poses a great treatment challenge. The objective of this paper is to present a unique case of giant nevi along with a review of the literature .

Great Ormond Street Hospital for Children Registry for Congenital Melanocytic Naevi: prospective study 1988-2007. Part 1-epidemiology, phenotype and outcomes

The aetiology of congenital melanocytic naevi (CMNs) is unknown. To identify potential aetiological factors in families of children with CMNs, and to relate these to long-term outcome measures. Three hundred and forty-nine CMN families completed questionnaires about pregnancy and parental factors, and yearly questionnaires on the health of their child and details of the CMN. Seventy-nine control families completed one set of questionnaires, excluding CMN details. The mean prospective follow-up of 301 CMN families was 9.2 years, median 8.9 years, total 2679 years. Forty per cent of patients had CMNs > 20 cm projected adult size (PAS) or multiple CMNs. Twenty per cent of patients had abnormal neurodevelopment and although this was positively associated with PAS it was seen across all size categories. The rate of malignant melanoma was 1.4%. This was strongly associated with PAS with all five cases in patients with CMNs > 60 cm PAS/multiple CMNs (rate in that group 14%). Twenty-five per cent of CMN patients had a positive family history of a CMN in a second-degree relative (FHCMN). This group had a significantly different gender ratio, suggesting a different underlying mutation. Maternal FHCMN was negatively associated with PAS and satellites at birth, and maternal freckling was negatively associated with PAS. Other factors found to be significantly increased in CMN families compared with controls were maternal smoking and ill health during pregnancy. Maternal smoking was positively associated with PAS. This study relies on data from families after they have had a child with a CMN, and therefore may be subject to recall bias. Despite this, it contributes significantly to the knowledge of epidemiology of CMNs, and provides some important clues to the genetic basis of the condition.

Complications of congenital melanocytic naevi in children: analysis of 16 years’ experience and clinical practice

Congenital melanocytic naevi (CMNs) can be associated with abnormalities of the cental nervous system (CNS) and/or with melanoma. Quoted incidences for these complications vary in the literature, as do recommendations for investigations and follow-up. To determine the incidence of complications, and to identify phenotypic features associated with a higher risk of complications. We reviewed records of 224 patients with CMNs seen in Dermatology clinic between 1991 and 2007. Patients were excluded if they had a complication at the time of referral. Magnetic resonance imaging (MRI) of the CNS was offered on the basis of CMN phenotype. Follow up was in clinic and/or by postal questionnaires. One hundred and twenty patients (54 boys and 66 girls) who had MRI of the CNS were included in the analysis. Mean age at MRI was 2.46 years (median 1.20). Mean follow up was 8.35 years (median 7.86). Sixty-five per cent had naevi > 20 cm projected adult size or multiple CMNs (40% > 40 cm), and 83% had satellite lesions at birth. Outcome measures were MRI abnormality, clinical neurological abnormality, any tumour, malignant melanoma, and death. No complications were seen in the 16 patients with no satellite lesions at birth. MRI and/or clinical neurological abnormalities were found in 22 patients (18%) and were significantly associated with projected adult size of the CMN (particularly > 40 cm), and independently with male gender. Tumours occurred in five patients, two of which were malignant melanoma (1.7%). Due to small numbers there was no significant association between phenotype and occurrence of tumours. Three patients (2.5%) died (one from neuromelanosis and two from melanoma in patients with normal MRI scans). Death was significantly associated with CMN size > 40 cm. Importantly, there was no significant association between CMN distribution (including posterior axial location) and adverse outcomes. This is the largest study of CNS imaging in patients with CMNs. We report a newly recognized association between male gender and neurological complications, dispute the previously reported association between CMN site and neurological complications, and quantify the associations between CMN size, satellite lesions and neurological complications. We make recommendations for the management of these patients.

Neurocutaneous Melanosis: A Case of Primary Intracranial Melanoma with Metastasis

Neurocutaneous melanosis is a rare disorder characterized by the presence of large or multiple congenital melanocytic naevi and benign or malignant pigment cell tumours of the leptomeninges. Distant metastasis is unusual in primary leptomeningeal/intracranial melanomas. We present the case history of an adult male who had multiple primary intracranial melanomas associated with neurocutaneous melanosis (naevus of Ota) in the ophthalmic division of the left trigeminal nerve. Excision of the intracranial tumours was carried out in two stages, but the patient died 2 days after the second operation. Autopsy showed multiple metastatic deposits in the liver. Symptoms and signs of raised intracranial pressure, the presence of Ota's naevus, and a dural-based mass or masses should alert the treating physician to suspect a primary leptomeningeal/intracranial melanoma.