BRAF mutations are common somatic events in melanocytic nevi

We determined mutations in the BRAF, N-ras, and CDKN2A genes in 27 histologically diverse melanocytic nevi and corresponding surrounding tissues from 17 individuals. Mutations in the BRAF and N-ras gene were found in 22 nevi (81%) from 16 individuals (94%). The predominant BRAF mutation T1799A (V600E) was detected in 18 nevi; 1 nevus had a novel A1781G (D594V) mutation in the same gene and 3 nevi had mutations in codon 61 of the N-ras gene. In 4 individuals both nevi carried a BRAF mutation, whereas in 2 other individuals 1 nevus showed a BRAF mutation and the second nevus had an N-ras mutation. In 2 individuals normal skin distant from nevi showed a BRAF mutation. No mutations were detected in the CDKN2A gene. The mutations in the BRAF and N-ras genes, in this study, were not associated with histologic type, location, skin type, size, or numbers of nevi. Our results suggest that mutations in the BRAF gene and to some extent in the N-ras gene represent early somatic events that occur in melanocytic nevi. We hypothesize the dual effect of solar ultraviolet irradiation on melanoma, through mutagenesis and by increasing the number of melanocytic nevi, many of which carry a BRAF or N-ras mutation.     

Congenital melanocytic nevi needing treatment

Patients presenting with congenital melanocytic nevi (CMN) need individualized treatment based upon nevus size, thickness, location, risk for developing melanoma, and psychological characteristics of the patient and family. The present authors review CMN types and prognoses, as well as absolute and relative indications for treatment. Risks and benefits of several treatment options are discussed, including surgical options, such as excision, chemical peels, dermabrasion and curettage, and laser therapy. The main focus of treatment is, in all cases, to address the concern for developing melanoma, at the same time optimizing the aesthetic and functional outcomes.     

Congenital melanocytic nevi. Evaluation and management

This article discusses the care of patients with CMN, who often require a multidisciplinary approach involving pediatricians, family physicians, internists, dermatologists, psychologists, plastic surgeons, neurologists, and radiologists. The cosmetic and psychosocial issues, combined with the knowledge of the increased risk of developing melanoma or NCM, is a huge burden that many of these patients and their families have to carry. This article describes the importance for physicians to help these patients and families come to terms with these issues, as well as remind their patients and their family members that although melanoma, NCM, or other complications can develop, most affected individuals do not develop any complications. The article mentions that there are many healthy, happy, functional adults with large, small, and multiple CMN alive today.     

Activating BRAF mutations in eruptive melanocytic naevi

Background Eruptive melanocytic naevi (EMN) are melanocytic proliferations developing rapidly on previously unaffected skin in association with various clinical scenarios, most commonly systemic immunosuppression. However, the exact mechanism leading to development of EMN is not understood. In particular, it is not known whether EMN harbour the BRAF mutations which occur frequently in melanoma and most common naevi. Objectives To evaluate whether activating BRAF mutations may play a role in genesis of EMN. Methods Genomic DNA was isolated from 20 EMN from a patient treated with 6‐mercaptopurine (6‐MP). Primary BRAF genotyping was performed by allele‐specific polymerase chain reaction, followed by validation using direct sequencing. Results The BRAF V600E mutation was identified in 85% of EMN examined. Conclusions Our results implicate mutational activation of the BRAF–MAPK pathway as a factor in development of EMN in the setting of 6‐MP treatment. The mechanism leading to development of EMN in this, and potentially other patients, may relate to synergistic mutagenic effects of thioguanines and ultraviolet (UV) A. Together with the documented importance of BRAF mutations in melanoma development and maintenance, these findings highlight the importance of UVA protection, especially in patients treated with thiopurines such as 6‐MP.     

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.     

Congenital acral melanocytic nevi clinically simulating acral lentiginous melanoma

Three cases of congenital acral melanocytic nevi with unusual clinical characteristics are reported. In all of the cases the surface changes and their growth were clinically suggestive of acral lentiginous melanoma, but biopsies revealed their benign nature. This exceptional presentation of congenital acral melanocytic nevi merits recognition by physicians and underscores the need for histologic diagnosis prior to definitive surgery in any cases suspected of being malignant melanoma.     

Congenital melanocytic nevi: treatment modalities and management options

Congenital melanocytic nevi can be cosmetically disfiguring, give rise to melanoma, and suggest the presence of neurocutaneous melanocytosis. Management decisions must be tailored for each patient and each nevus, taking into consideration the risk for developing malignancy, risk for developing symptomatic neurocutaneous melanocytosis, cosmetic implications of having the nevus, cosmetic implications of any resultant surgical scars from their removal, adverse effects that the nevus may have on psycho-social development, and the adverse effects and long-term sequelae of any surgical intervention. The advantages and disadvantages of different modalities used in the treatment of congenital melanocytic nevi are discussed. Organizational flow diagrams are presented to help clinicians in managing patients with different sized congenital melanocytic nevi.     

Congenital melanocytic nevi: treatment modalities and management options

Congenital melanocytic nevi can be cosmetically disfiguring, give rise to melanoma, and suggest the presence of neurocutaneous melanocytosis. Management decisions must be tailored for each patient and each nevus, taking into consideration the risk for developing malignancy, risk for developing symptomatic neurocutaneous melanocytosis, cosmetic implications of having the nevus, cosmetic implications of any resultant surgical scars from their removal, adverse effects that the nevus may have on psycho-social development, and the adverse effects and long-term sequelae of any surgical intervention. The advantages and disadvantages of different modalities used in the treatment of congenital melanocytic nevi are discussed. Organizational flow diagrams are presented to help clinicians in managing patients with different sized congenital melanocytic nevi.     

Lack of association between BRAF mutation and MAPK ERK activation in melanocytic nevi

The mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase signaling pathway can be activated through mutations of V-RAF murine sarcoma viral oncogene homolog B1 (BRAF) oncogene, frequently found in melanoma (60%), common nevi (CN) (73-82%), and atypical nevi (AN) (52-80%). MAPK activation has been reported between 0 and 22% in nevi, and 86% of primary melanoma, without any knowledge of BRAF mutational status. We studied the correlation of MAPK activation status, BRAF mutation, and B-Raf expression in CN, AN, and melanoma. Using immunohistochemistry, phosphorylated (active) MAPK and B-Raf expression was studied in 24 CN, 21 AN, and 26 primary cutaneous melanomas (PM). BRAF mutations at codon 600 were assessed by PCR-RFLP. Active MAPK was detected in 29% of CN, 48% of AN, and 85% of PM. BRAF mutation was found in 67% of CN, 62% of AN, and 58% of PM. In all, 23% of CN, 54% of AN, and 93% of PM with BRAF mutation have activated MAPK. All lesions expressed B-Raf. BRAF mutation does not seem to be sufficient to produce MAPK activation in melanocytic nevi, and it is suggested that other events are needed to induce MAPK activation, that is, B-Raf overexpression, inhibition of MAPK phosphatases, or suppression of RAF kinase inhibitors.     

Low prevalence of RAS-RAF-activating mutations in Spitz melanocytic nevi compared with other melanocytic lesions

Melanocytic lesions, including Spitz nevi (SN), common benign nevi (CBN) and cutaneous metastatic melanoma (CMM), were analyzed for activating mutations in NRAS, HRAS and BRAF oncogenes, which induce cellular proliferation via the MAP kinase pathway. One of 22 (4.5%) SN tested showed an HRAS G61L mutation. Another lesion, a 'halo' SN, showed a BRAF V600E (T1796A) mutation. BRAF V600E mutations were found in two thirds (20/31) of CBN, while a further 19% (6/31) showed NRAS codon 61 mutations. One third of CMM (10/30) had various BRAF mutations of codon 600, and a further 6% (2/31) showed NRAS codon 61 mutations. Seventeen SN tested for loss of heterozygosity (LOH) at 9p and 10q regions, known to be frequently deleted in melanoma, showed LOH at the 9p loci D9S942 and IFNA. A further lesion was found with low-level microsatellite instability at one locus, D10S214. The low rate of RAS-RAF mutations (2/22, 9.1%) observed in SN suggests that these lesions harbor as yet undetected activating mutations in other components of the RAS-RAF-MEK-ERK-MAPK pathway. Germline DNA from members of 111 multiple-case melanoma families, representing a range of known (CDKN2A) and unknown predisposing gene defects, was analyzed for germline BRAF mutations, but none was found.     

BRAF and NRAS mutations are frequent in nodular melanoma but are not associated with tumor cell proliferation or patient survival

Previous studies have shown frequent mutations in the BRAF (V-raf murine sarcoma viral oncogene homolog B1) or NRAS (neuroblastoma RAS viral [V-ras] oncogene homolog) genes in cutaneous melanoma, but the relationship between these alterations and tumor cell proliferation has not been examined in human melanoma. In our study of 51 primary nodular melanomas and 18 paired metastases, we found mutations in BRAF (codon 600, previously denoted 599) in 15 primary tumors (29%) and eight metastases (44%). The figures for NRAS mutations were 27% and 22%, respectively. Mutations in BRAF and NRAS genes were mutually exclusive in all but one case, and were maintained from primary tumors through their metastases. Mutations, however, were not associated with tumor cell proliferation by Ki-67 expression, tumor thickness, microvessel density, or vascular invasion, and there were no differences in patient survival. Although BRAF and NRAS mutations are likely to be important for the initiation and maintenance of some melanomas, other factors might be more significant for proliferation and prognosis in subgroups of aggressive melanoma.     

BRAF, NRAS and HRAS mutations in spitzoid tumours and their possible pathogenetic significance

Background The relationships between so‐called spitzoid tumours have proven difficult to understand. Objectives To address three questions: does spitzoid tumour morphological similarity reflect molecular similarity? Does Spitz naevus progress into spitzoid melanoma? Are ambiguous spitzoid tumours genuine entities? Methods BRAF, NRAS and HRAS mutations were analysed using single‐strand conformational polymorphism analysis and sequencing. Results Both Spitz naevi and spitzoid melanoma had a lower combined BRAF and NRAS mutation frequency compared with common acquired naevi (P = 0·0001) and common forms of melanoma (P = 0·0072), respectively. To look for evidence of progression from Spitz naevi to spitzoid melanoma, HRAS was analysed in 21 spitzoid melanomas, with no mutations identified. The binomial probability of this was 0·03 based on an assumption of a 15% mutation frequency in Spitz naevi with unbiased progression. Under these assumptions, HRAS mutations must be rare/absent in spitzoid melanoma. Thus, Spitz naevi seem unlikely to progress into spitzoid melanoma, implying that ambiguous spitzoid tumours cannot be intermediate degrees of progression. In addition, the data suggest that HRAS mutation is a potential marker of benign behaviour, in support of which none of three HRAS mutant spitzoid cases metastasized. Conclusions First, the morphological similarity of spitzoid tumours reflects an underlying molecular similarity, namely a relative lack of dependence on BRAF/NRAS mutations. Second, Spitz naevi do not appear to progress into spitzoid melanoma, and consequently ambiguous spitzoid tumours are likely to be unclassifiable Spitz naevi or spitzoid melanoma rather than genuine entities. Third, HRAS mutation may be a marker of Spitz naevus, raising the possibility that other molecular markers for discriminating Spitz naevi from spitzoid melanoma can be discovered.     

Examination of mutations in BRAF, NRAS, and PTEN in primary cutaneous melanoma

Frequent somatic mutation of v-raf murine sarcoma viral oncogene homolog B (BRAF), a downstream effector of the rat sarcoma oncogene (RAS) signaling pathway, is described in melanoma and other tumors. Our analysis of melanoma cell lines suggests that activating mutations in BRAF can occur simultaneously with inactivation of phosphatase and tensin homolog (PTEN), but neuroblastoma RAS (NRAS) mutations are not coincident. We determined the concurrent prevalence of mutations in BRAF and NRAS, and alteration of PTEN expression in 69 primary cutaneous melanomas. BRAF mutations were seen in 57% of cases. NRAS was mutated in 17% of samples, exclusively in exon 2. Two cases showed concurrent BRAF and NRAS mutations. Using immunohistochemistry, PTEN protein expression was lost or greatly reduced in 19% of tumors. Seven tumors with reduced PTEN yielded DNA amenable to sequencing, and three also showed mutation in BRAF but none in NRAS. In all, 11 (85%) of 13 tumors showing reduced PTEN expression were greater than 3.5 mm thick, and the association of increasing Breslow thickness and loss or reduction of PTEN expression was statistically significant (P<0.0001). Mutations in NRAS were not coincident with reduced PTEN expression, and the concurrent mutation of NRAS and BRAF was rare.     

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.     

Genetic interaction between NRAS and BRAF mutations and PTEN/MMAC1 inactivation in melanoma

Extant evidence implicates growth factor signaling in the pathogenesis of many tumor types, including cutaneous melanoma. Recently, reciprocal activating mutations of NRAS and BRAF were found in benign melanocytic nevi and cutaneous melanomas. We had previously reported a similar epistatic relationship between activating NRAS mutations and inactivating PTEN/MMAC1 alterations. We thus hypothesized that BRAF and PTEN/MMAC1 mutations may cooperate to promote melanoma tumorigenesis. Overall, 40 of 47 (85%) melanoma cell lines and 11 of 16 (69%) uncultured melanoma metastases had mutations in NRAS, BRAF, or PTEN/MMAC1. NRAS was exclusively mutated in nine of 47 (19%) cell lines and two of 16 (13%) metastases, whereas BRAF was solely mutated in 28 of 47 (60%) cell lines and nine of 16 (56%) metastases. In the 12 of 15 melanoma cell lines (80%) and two of two melanoma metastases with PTEN alterations, BRAF was also mutated. These findings suggest the existence of possible cooperation between BRAF activation and PTEN loss in melanoma development.