Distinct phenotypic changes between the superficial and deep component of giant congenital melanocytic naevi: a rationale for curettage

Additional treatments after curettage of congenital melanocytic nevi in the craniofacial region: A report from a single center in Japan

BACKGROUND

Congenital melanocytic nevus (CMN) is a benign skin lesion present from birth, which may present with a risk of malignant transformation if extensive. Curettage, a treatment method involving the removal of the superficial layer of the nevus, is often used in the early stages of life. However, recurrence of the nevus and postoperative scarring may present as problems. Additional treatments, such as resection and/or laser treatment, are regularly required after curettage, particularly in the craniofacial region. However, no systematic treatment strategy has been reported. This study investigated additional treatments used after curettage to treat CMN in the craniofacial region and compared the frequency of treatments with respect to specific sites.

METHODS

CMN cases involving curettage as an initial treatment were retrospectively reviewed at Kyoto University Hospital between May 2019 and April 2022.

RESULTS

This study comprised 23 cases. Curettage was performed at a mean of 3.8 (1-10) months of age. No additional treatments were provided for 80% of head CMN. Additional treatments were performed in all cases, including the forehead and cheek. Laser treatment was performed in 86% of eyelid CMN and 75% of nasal CMN. Tissue expansion and flap closure were used in 33% of forehead CMN and 33% of cheek CMN.

CONCLUSIONS

Additional treatments used for CMN in the craniofacial region varied in accordance with the lesion site.

Prevalence, incidence density and standardized morbidity rate of melanoma among patients with congenital melanocytic naevi: a systematic review

BACKGROUND

Congenital melanocytic naevi (CMN) are the result of aberrations in the mitogen-activated protein kinase signal transduction pathway. The risk of melanoma is the most important concern among patients with CMN because of its poor prognosis. However, as a result of the great variability between studies, the reported risk of melanoma varies considerably, making it difficult to provide reliable information.

OBJECTIVES

To evaluate the prevalence, incidence density and standardized morbidity ratio (SMR) of melanoma among patients with CMN.

METHODS

We conducted a systematic literature search of studies providing data on the risk of melanoma in patients with CMN following our registered and published protocol (PROSPERO: CRD42022383009).

RESULTS

Overall, 27 studies with a total of 11 480 patients with CMN and 82 patients developing melanoma were included for analysis. The prevalence of melanoma was 1.84% [95% confidence interval (CI) 1.13-2.99] in patients with CMN and 2.73% (95% CI 1.67-4.43) in the subgroup of patients with large CMN (LCMN). The incidence of melanoma was 237.56 (95% CI 97.79-575.96) per 100 000 person-years in patients with CMN and 585.73 (95% CI 315.39-1085.29) per 100 000 person-years in the LCMN subgroup. The SMR of melanoma was 122.27 (95% CI 11.84-1262.88) among all patients with CMN and 285.97 (95% CI 50.65-1614.59) in the subgroup of patients with LCMN.

CONCLUSIONS

Our research suggests that the risk of melanoma in the CMN population seems to have been overestimated in previous studies, but it is still significantly higher than that in the general population. In addition to the risk of melanoma, aesthetic improvement and mental health should also be taken into account when making management decisions.

Erbium: YAG laser treatment efficacy and association with histologic features for giant congenital melanocytic nevi management

BACKGROUND

Limited research exists on laser treatment of giant congenital melanocytic nevus (GCMN).

OBJECTIVE

We sought to elucidate the efficacy of the Erbium: YAG laser on GCMN and the histologic factors associated with a positive clinical response.

METHODS AND MATERIALS

Between 2019 and 2022, we enrolled 30 medium-to-giant CMN patients who underwent Er: YAG laser treatment. All patients received biopsies before and after laser treatments. Clinical efficacy outcomes were evaluated by the investigator's global assessment (IGA), 5-point scale of depigmentation, and Vancouver Scar Scale (VSS) scores at least 6 months after treatment.

RESULTS

Of the 30 cases, 18 (60.0%) showed improvement (IGA score ≥3). Eight (26.7%) patients showed repigmentation. Eight (26.7%) patients developed hypertrophic scars. The average IGA, depigmentation, and VSS scores were 2.93, 3.57, and 3.20. The IGA score was higher (3.24 ± 1.18 vs. 2.22 ± 0.97, p = 0.031) and a lower repigmentation rate (14.3% vs. 55.6%, p = 0.032) was observed in the cases with Grenz zone. The IGA score was higher (3.33 ± 1.24 vs. 2.13 ± 0.89, p = 0.023) and the repigmentation rate was lower (11.1% vs. 50.0%, p = 0.034) also in the cases with the melanocytes nests with aggregation of melanin. Lesions with superficial ablation resulted in less hypertrophic scar formation than those with deep ablation (5.9% vs. 53.8%, p < 0.05).

CONCLUSION

The Er: YAG laser demonstrated effective clinical results for GCMNs. The grenz zone and the melanocytes nests with aggregation of melanin are promising predictors of laser efficacy.

Risk of melanoma in congenital melanocytic nevi of all sizes: A systematic review

Congenital melanocytic nevi (CMN) are commonly encountered benign skin lesions in newborns. Larger CMN is associated with a higher lifetime risk of developing melanoma. However, the level of risk is unclear when CMN are small or medium-sized. Our objective was to assess melanoma risk in patients with CMN of all size categories. A literature review with meta-analysis was performed. Prevalence and incidence densities of melanoma at onset were calculated in the entire study population and according to CMN size, type of treatment and location of the CMN. A total of 91 melanomas were reported in 7915 patients (1.15%, 95% CI, 0.93-1.41). The overall incidence density was 0.057% person-years (95% CI_, 0.044-0.071). The risk ratio of melanoma incidence densities was 21.9 (95% CI, 8.55-56.3) in large to giant CMN compared with small to medium CMN at 15 years of age. The incidence density was higher in CMN located on the trunk and as well as in those which were untreated or partially treated versus complete excision. Our review suggests patients with CMN of medium, large and giant size are at risk of melanoma, whereas the risk remains unknown for small CMN.

Neonatal Curettage of Large to Giant Congenital Melanocytic Nevi Under Local Anesthetic: A Case Series With Long-Term Follow Up

Background

Neonatal curettage of large to giant congenital melanocytic nevi (L-GCMN) is a simple, minimally invasive procedure typically performed within the first 2 weeks of life.

Objectives

To retrospectively review our experience with serial curettage of L-GCMN in the neonatal period performed under local anesthesia and their long-term outcomes.

Methods

Curettage was performed by a single pediatric dermatologist on nine neonates with L-GCMN under local anesthetic and with oral analgesia between 2002 and 2016 in Red Deer, Alberta, Canada. Patient charts were reviewed retrospectively to assess patient and procedure characteristics, tolerability, safety, cosmetic and functional outcomes, and malignant transformation.

Results

Patients were treated with an average of 6 curettage sessions (range 3 to 15) to remove the majority or entirety of the nevus. All patients tolerated local anesthesia well. The most common adverse event of the procedure was transient neutropenia. Two patients developed positive bacterial cultures without clinical signs of infection, treated with antibiotics. All curetted specimens demonstrated benign pathology. Patients were followed annually thereafter, for an average of 6 years. Eight patients with L-GCMN of the trunk had minimal to partial repigmentation with good cosmetic outcome. One patient had recurrence of a facial nevus. None of the patients developed cutaneous malignant melanoma.

Conclusions

Curettage appears to be a safe and effective treatment option for select cases of L-GCMNs of the trunk. We do not recommend the procedure for face or scalp CMN. This procedure can be performed under local anesthesia with serial curettage to avoid potential risks of general anesthesia.

Genetics of melanocytic nevi

Melanocytic nevi are a benign clonal proliferation of cells expressing the melanocytic phenotype, with heterogeneous clinical and molecular characteristics. In this review, we discuss the genetics of nevi by salient nevi subtypes: congenital melanocytic nevi, acquired melanocytic nevi, blue nevi, and Spitz nevi. While the molecular etiology of nevi has been less thoroughly studied than melanoma, it is clear that nevi and melanoma share common driver mutations. Acquired melanocytic nevi harbor oncogenic mutations in BRAF, which is the predominant oncogene associated with melanoma. Congenital melanocytic nevi and blue nevi frequently harbor NRAS mutations and GNAQ mutations, respectively, while Spitz and atypical Spitz tumors often exhibit HRAS and kinase rearrangements. These initial 'driver' mutations are thought to trigger the establishment of benign nevi. After this initial phase of the cell proliferation, a senescence program is executed, causing termination of nevi growth. Only upon the emergence of additional tumorigenic alterations, which may provide an escape from oncogene-induced senescence, can malignant progression occur. Here, we review the current literature on the pathobiology and genetics of nevi in the hope that additional studies of nevi promise to inform our understanding of the transition from benign neoplasm to malignancy.

Giant congenital melanocytic nevus: report from 30 years of experience in a single department

Giant congenital melanocytic nevi (GCMN) occur in 1:20,000 livebirths and are associated with increased risk of malignant transformation. The treatment of GCMN from 1981 to 2010 in a tertiary referral center was reviewed evaluating the modalities used, cosmetic results, associated complications, and malignant transformation. Of 35 patients, 25 underwent surgery. Curettage was most frequently used (64%) followed by excision and tissue expansion (20%). Six percent of the patients treated with curettage, and 78% of the patients who received excision surgery required more than 1 planned procedure, and 25% versus 44% required unplanned additional surgery, respectively. Complications were noted in 25% and 67% of the patients, respectively. Cosmetic result was satisfying in 76% of patients without difference between the groups. No malignant transformation was found during a mean follow-up of 11 years. Curettage is a gentle alternative to excision with a lower complication rate and good cosmetic outcome.

Update on melanocytic nevi in children

A new or changing melanocytic nevus in a child or adolescent often leads to concern in parents and physicians. To avoid undue alarm and unnecessary procedures, dermatologists should be aware of the natural history and clinical spectrum of nevi in pediatric patients, as well as findings that are potentially worrisome in this age group. This review provides an update on melanocytic nevi in children, focusing on their dynamic evolution over time, molecular insights into nevogenesis, and phenotypic markers for increased risk of melanoma in adolescence and adulthood. Special considerations for Spitz nevi and nevi located in particular sites (eg, scalp, acral, genital) are highlighted. Current understanding of the risks associated with congenital melanocytic nevi of different sizes and strategies for the management of children with numerous acquired nevi, Spitz nevi, and congenital nevi are also discussed.

Hydrosurgery, a new therapeutic perspective in early care of giant congenital nevi: a preliminary series of four cases

BACKGROUND

Congenital melanocytic nevi are present at birth or may appear in the first weeks of life. Small and medium-size lesions are relatively common, affecting approximately 1% of newborns; large or giant melanocytic nevi occur in 1/20,000-1/500,000 births. The main concern raised by these lesions is their potential risk of degeneration which is strongly size-dependent and estimated in the literature between 0% and 40% over a lifetime. Although multiple treatment modalities have been described, to date there is no consensus regarding their optimal management.

PATIENTS AND METHODS

Four neonates (three females and one male) presenting giant congenital nevi with a mean age 12 days (7-24 days) were referred to our Plastic Surgery department for treatment from 2012 to 2013. All patients underwent an alternative dermabrasion procedure with the innovative use of hydrosurgery. All procedures were performed under general anaesthesia by the same senior operator (Dr. B.Bayet).

RESULTS

The mean operating time was significantly reduced compared to conventional techniques. No complications were observed in the postoperative course. Good final results were obtained in three patients after a mean follow-up of respectively 11, 8 and 4 months. The first operated neonate showed a complete recurrence of pigmentation of the treated areas after 6 months.

CONCLUSIONS

The need for early treatment in giant congenital nevi is admitted by all. Hydrosurgery is easy to use and allows to achieve a selective and symmetric resection with an obvious cleavage plane and clean-cut borders. Furthermore, this procedure has convinced us with its speed of use, ensuring significant time saving, and therefore less morbidity for the neonate. Aesthetic results as well as recurrence rate may be comparable to conventional techniques. However, regular follow-up to detect any malignancy is necessary.

Lack of BRAF(V600E) mutations in giant congenital melanocytic nevi in a Chinese population

Giant congenital melanocytic nevi (CMNs) are at an increased risk for malignant transformation. To explore the mutation frequencies of BRAF(V600E) (V-raf murine sarcoma virus oncogene homolog B1) and NRAS (neuroblastoma ras viral oncogene homolog) codon 61 in CMNs of Chinese, we selected 55 paraffin-embedded tissue blocks, including 37 cases of medium CMNs (1.5-20cm) and 18 cases of giant CMNs (>20 cm). Direct sequencing was performed to detect the BRAF(V600E) and NRAS codon 61 mutations. The BRAF(V600E) mutations were detected in 9 of 55 nevi (16.4%). In medium CMNs, 9 of 37 BRAF(V600E) mutations (24.3%) were detected. Notably, in giant CMNs, no BRAF(V600E) mutations were found. The difference between these frequencies is statistically significant (P = 0.0231). NRAS codon 61 mutations were detected in 13 of 55 nevi (23.6%), including 10 of 37 medium CMNs (27.0%) and 3 of 18 giant CMNs (16.7%). Additionally, the BRAF(V600E) and NRAS codon 61 mutations did not coexist in the same sample. Finally, we found that the NRAS codon 61 mutation was significantly related to the amount of sun exposure (0 of 18 CMNs from sites of intermittent sun exposure and 13 of 36 CMNs from sites of chronic continuous sun exposure, P = 0.0024). The paradoxically higher incidence of BRAF(V600E) mutations in medium-sized compared with giant CMNs suggests that the presence of the BRAF(V600E) mutation may play different roles between medium and giant CMNs in melanocytic tumorigenesis.

Molecular nevogenesis

Despite recent advances, the biology underlying nevogenesis remains unclear. Activating mutations in NRAS, HRAS, BRAF, and GNAQ have been identified in benign nevi. Their presence roughly correlates with congenital, Spitz, acquired, and blue nevi, respectively. These mutations are likely to play a critical role in driving nevogenesis. While each mutation is able to activate the MAP kinase pathway, they also interact with a host of different proteins in other pathways. The different melanocytic developmental pathways activated by each mutation cause the cells to migrate, proliferate, and differentiate to different extents within the skin. This causes each mutation to give rise to a characteristic growth pattern. The exact location and differentiation state of the cell of origin for benign moles remains to be discovered. Further research is necessary to fully understand nevus development given that most of the same developmental pathways are also present in melanoma.

Large congenital melanocytic nevi: associated risks and management considerations

Large congenital melanocytic nevi (LCMN) in neonates can cause considerable concern for parents, family members, and physicians. A detailed understanding of the medical risks, including cutaneous melanoma (CM), extracutaneous melanoma (ECM), and neurocutaneous melanocytosis (NCM), as well as the psychological stress that these lesions can cause in patients, will guide informed management decisions as well as provide comfort to parents. Current data indicate that LCMN greater than 20 cm, and more likely greater than 40 to 60 cm, are the lesions at greatest risk for complications such as CM, ECM, and NCM. Additionally, lesions on the trunk are at greater risk for developing CM, and LCMN in association with numerous satellite nevi are at greatest risk for NCM. Individualized management plans, including clinical observation, magnetic resonance imaging (MRI), and possibly surgery should be based on the risk versus benefit ratio, taking into account the size of the LCMN, its location, the number of satellite nevi, symptoms, and numerous other factors which will be reviewed. This paper will provide a detailed analysis of the risks associated with LCMN, as well as a discussion regarding management and treatment options.

Congenital melanocytic nevi-when to worry and how to treat: Facts and controversies

Congenital melanocytic nevi (CMN) are evident in 1% to 6% of neonates. In some studies, nevi with clinical, dermatoscopic, and histologic features identical to CMN have had a prevalence of more than 15% in older children and adults, possibly reflecting the "tardive" appearance of nevi programmed from birth. There is ongoing debate about the magnitude of the risk of melanoma and other complications associated with CMN of various sizes and the best approach to management of these lesions. We review the natural history of CMN, including proliferative nodules and erosions during infancy, neurotization, and spontaneous regression, and features of variants such as speckled lentiginous and congenital blue nevi. The risk of melanoma arising within small-sized (<1.5 cm) and medium-sized CMN is low (likely <1% over a lifetime) and virtually nonexistent before puberty. Recent data suggest that melanoma (cutaneous or extracutaneous) develops in approximately 5% of patients with a large (>20 cm) CMN, with about half of this risk in the first few years of life. Melanoma and neurocutaneous melanocytosis (NCM) are most likely in patients with CMN that have a final size of >40 cm in diameter, numerous satellite nevi, and a truncal location. One-third of individuals with NCM have multiple medium-sized (but no large) CMN. In patients at risk for NCM, a screening gadolinium-enhanced magnetic resonance imaging, preferably before age 6 months, and longitudinal neurologic assessment are recommended. Management of CMN depends on such factors as the ease of monitoring (more difficult for large, dark, thick nevi) and cosmetic and psychologic benefits of excision or other procedures. CMN require lifelong follow-up. Periodic total body skin examinations are necessary for all patients with large CMN, even when complete resection (often impossible) has been attempted.

Familial clustering of giant congenital melanocytic nevi

Giant congenital melanocytic nevus (GCMN) is an infrequently occurring congenital malformation. GCMN generally occurs in isolation but rare familial occurrence points to a genetic background. We present two cases of familial GCMN: one with two affected siblings and another with two affected double second cousins. Familial occurrence of GCMN reported in literature is reviewed and an overview of the embryology and proliferation given, illustrating the plethora of factors that might lead to GCMN formation. The pattern of inheritance is likely not Mendelian and discordance in identical twins and the segmental distribution of lesions suggest a post-zygotic mutation. A polygenic paradominant inheritance best explains the clinically observed transmission pattern. Candidate genes include those influencing neural crest development and melanocyte proliferation.

The role of surgery in the management of congenital melanocytic naevi in children: a perspective from Great Ormond Street Hospital

Recent advances in research have prompted this review of the role of surgery in the management of congenital melanocytic naevi (CMNs). Good data on the incidence of neurological and malignant complications of CMNs have re-fuelled the debates on whether surgery decreases the risk of malignant melanoma and whether early surgery is advantageous. We conclude the following: 1) untreated CMNs can lighten spontaneously, sometimes dramatically, 2) routine surgery has not been demonstrated to reduce the risk of malignancy and is, therefore, for cosmetic reasons only, 3) early surgery has not been shown to be advantageous and carries increased anaesthetic risk and 4) there is some evidence that surgical intervention may adversely affect the behaviour of the CMN cells. Our current practice is based on the following guidelines: 1) patients are treated in a multidisciplinary-team setting which includes the specialties of paediatric dermatology, plastic surgery and neuroradiology with access to neurology, neurosurgery and oncology, 2) serial photographs are taken at yearly intervals to assess spontaneous lightening. 3) all routine surgery is delayed for at least the first year. 4) patients with facial CMNs (either the principal lesion or large satellites) are offered surgery for cosmetic reasons, 5) patients with a single, easily excisable CMN are offered surgery for cosmetic reasons and 6) all families are made aware of the possibility of spontaneous lightening and the possibility that surgery may have effects on the behaviour of naevus cells.

Type I collagen expression contributes to angiogenesis and the development of deeply invasive cutaneous melanoma

Tumors are complex tissues composed of neoplastic cells, soluble and insoluble matrix components and stromal cells. Here we report that in melanoma, turn-over of type I collagen (Col(I)), the predominant matrix protein in dermal stroma affects melanoma progression. Fibroblasts juxtaposed to melanoma cell nests within the papillary dermis display high levels of Col(I) mRNA expression. These nests are enveloped by collagen fibers. In contrast, melanoma-associated fibroblasts within the reticular dermis express Col(I) mRNA at a level that is comparable to its expression in uninvolved dermis and reduced amount of collagen protein can be observed. To determine the significance of Col(I) expression in melanoma, we pharmacologically inhibited its transcription in a porcine cutaneous melanoma model by oral administration of halofuginone. When administered before melanoma development, it reduced melanoma incidence and diminished the transition from microinvasive toward deeply invasive growth by limiting the development of a tumor vasculature. Whereas invasive melanoma growth has been correlated with increased blood vessel density previously, our data for the first time demonstrate that the proangiogenic effect of Col(I) expression by fibroblasts and vascular cells precedes the development of invasive melanomas in a de novo tumor model.

Distribution of BRAF T1799A(V600E) mutations across various types of benign nevi: implications for melanocytic tumorigenesis

PURPOSE

The BRAF mutation is common in melanomas, but variation in rates across melanoma subtypes points to a complex interplay between BRAF activation and other factors (eg, sun exposure). Nevi also harbor the BRAF mutation. A description of mutation distribution in nevi could provide insight into the significance of this event in melanocytic tumorigenesis.

EXPERIMENTAL DESIGN

One hundred thirty-five nevi from 116 patients were evaluated for the T-->A mutation at nucleotide 1799. The nevi were inclusive of congenital (n = 34) and acquired (n = 101) nevi, dysplastic (n = 11) and nondysplastic (n = 124) nevi, and anogenital (n = 24) and common cutaneous (n = 111) nevi.

RESULTS

The overall mutation rate was 81%. The rate varied only slightly by anatomic site: BRAF mutations were detected in 21 of 21 (100%) nevi of the head and neck, 62 of 76 (82%) nevi of the trunk, 8 of 14 (62%) nevi of the extremities, and 18 of 24 (75%) anogenital nevi. For acquired nevi, there was no association between BRAF mutations and sun exposure as inferred from anatomic site. There were no significant differences in the mutation rates between congenital and acquired nevi (76% versus 81%; P = 0.5).

CONCLUSIONS

The BRAF mutation is uniformly distributed in various types of nevi. Its presence in congenital and anogenital nevi points to mechanisms of induction other than sun exposure. Its ubiquitous presence suggests that it poses no significant threat of malignant transformation, raising doubts about its relevance in melanoma development and its suitability as a target of directed therapy in patients with melanoma.

BRAF(E600) in benign and malignant human tumours

Of the RAF family of protein kinases, BRAF is the only member to be frequently activated by mutation in cancer. A single amino acid substitution (V600E) accounts for the vast majority and results in constitutive activation of BRAF kinase function. Its expression is required to maintain the proliferative and oncogenic characteristics of BRAF(E600)-expressing human tumour cells. Although BRAF(E600) acts as an oncogene in the context of additional genetic lesions, in primary cells it appears to be associated rather with transient stimulation of proliferation. Eventually, BRAF(E600) signalling triggers cell cycle arrest with the hallmarks of cellular senescence, as is illustrated by several recent studies in cultured cells, animal models and benign human lesions. In this review, we will discuss recent advances in our understanding of the role of BRAF(E600) in benign and malignant human tumours and the implications for therapeutic intervention.

Chromosomal translocations as a mechanism of BRAF activation in two cases of large congenital melanocytic nevi

Genetic studies of melanocytic tumors have mainly demonstrated activation of oncogenes such as NRAS or BRAF through point mutations. In two cases of large congenital melanocytic nevi, we observed a chromosomal translocation involving the BRAF oncogene on chromosome 7q34, resulting in both cases in removal of the auto-inhibitory N-terminal regulatory domain (hence the Ras-guanosine triphosphate binding domain) of BRAF from its protein kinase domain. This is early evidence of BRAF activation through chromosomal translocation in melanocytic tumors. Because BRAF point mutations are rather rare in congenital melanocytic nevi and melanoma arising in non-sun-exposed area, the molecular mechanism of oncogenic activation as described here could be a recurrent molecular feature in these groups of melanocytic tumors.

High Frequency of BRAFV600E Mutation in Acquired Nevi and Small Congenital Nevi, but Low Frequency of Mutation in Medium-Sized Congenital Nevi

To investigate whether the frequency of the BRAF(V600E) (V-raf murine sarcoma virus oncogene homolog B1) mutation in melanocytic nevi is associated with sun exposure patterns, we examined 120 acquired melanocytic nevi excised from various anatomic sites, including glabrous skin, as well as 62 congenital nevi. We used a new mutation detection system based on the shifted termination assay, called Mutector, which was able to detect only 5% of heterozygous mutant cells within the samples. We detected the mutation in 105/120 (87.5%) acquired nevi and 43/62 (69.4%) congenital nevi. Notably, we found the mutation in 35/43 (81.4%) acquired nevi excised from glabrous skin and genitalia. These results strongly suggest that UV light is not necessarily required for the acquisition of the BRAF(V600E) mutation, and suggest that non-mutagenic effects of UV light to melanocytes may be more important in the nevogenesis. Additionally, we showed heterogeneous distribution of BRAF-mutated cells within the lesions of small congenital nevi by a combination of laser microdissection and direct sequencing. Finally, we found low frequency of BRAF(V600E) mutation (6/20, 30.0%) in medium-sized congenital nevi. Most of these nevi with wild-type BRAF had neroblastoma ras viral oncogene homolog mutations (9/14, 64.3%), suggesting different pathogenesis of medium-sized congenital nevi from acquired nevi and small congenital nevi.

Congenital melanocytic nevi frequently harbor NRAS mutations but no BRAF mutations

Most melanocytic nevi develop on sun-exposed skin during childhood and adolescence and commonly harbor BRAF mutations or, less frequently, NRAS mutations. A small subset of nevi is present at birth, and therefore must develop independently of UV light. To assess whether these nevi have a different mutation spectrum than those that develop on sun-exposed skin, we determined the BRAF and NRAS mutation frequencies in 32 truly congenital nevi. We found no BRAF mutations, but 81% (26/32) harbored mutations in NRAS. Consistently, seven of 10 (70%) proliferating nodules that developed early in life in congenital nevi showed mutations in NRAS. A separate set of nevi that displayed histological features frequently found in nevi present at birth ("congenital pattern nevi") but lacked a definitive history of presence at birth showed an inverse mutation pattern with common BRAF mutations (20/28 or 71%) and less frequent NRAS mutations (7/28 or 25%). Thus, nevi that develop in utero are genetically distinct from those that develop later, and histopathologic criteria alone are unable to reliably distinguish the two groups. The results are consistent with the finding in melanoma that BRAF mutations are uncommon in neoplasms that develop in the absence of sun-exposure.

Genetic alterations in melanocytic tumors

In the last decade, significant progress has been made in our understanding of the genetic alterations in melanocytic tumors. The most exciting finding is the discovery of oncogenic BRAF mutations in both malignant melanoma and melanocytic nevi. This finding indicates that activation of the mitogen-activated protein kinase pathway may be a critical initiating step of melanocytic neoplasia, and that the fundamental difference between melanoma and nevi may lie in the inhibitory machinery for this oncogenic signaling. In addition, different genetic alterations identified in melanomas at different sites and with different levels of sun exposure have been shown, indicating that there are several distinct genetic pathways in the development of melanoma. Different patterns of genetic alterations have also been identified among different kinds of melanocytic nevi. While acquired nevi and small congenital nevi show a high frequency of BRAF mutations regardless of their anatomic localization, the mutations were rare in medium-sized congenital nevi and giant congenital nevi. Spitz nevi show no BRAF mutations, while a subset of cases show HRAS mutations, often associated with a copy number increase of chromosome 11p. The clear differences in genetic aberration patterns have significant clinical implications in the diagnosis and treatment of melanocytic tumors.