The BRAF V600K mutation is more frequent than the BRAF V600E mutation in melanoma in situ of lentigo maligna type

Heterogeneous pathogenesis of melanoma: BRAF mutations and beyond

Melanoma pathogenesis, conventionally perceived as a linear accumulation of molecular changes, discloses substantial heterogeneity driven by non-linear biological processes, including the direct transformation of melanocyte stem cells. This heterogeneity manifests in diverse biological phenotypes and developmental states, influencing variable responses to treatments. Unveiling the aberrant mechanisms steering melanoma initiation, progression, and metastasis is imperative. Beyond mutations in oncogenic and tumor suppressor genes, the involvement of distinct molecular pathways assumes a pivotal role in melanoma pathogenesis. Ultraviolet (UV) radiations, a principal factor in melanoma etiology, categorizes melanomas based on cumulative sun damage (CSD). The genomic landscape of lesions correlates with UV exposure, impacting mutational load and spectrum of mutations. The World Health Organization's 2018 classification underscores the interplay between sun exposure and genomic characteristics, distinguishing melanomas associated with CSD from those unrelated to CSD. The classification elucidates molecular features such as tumor mutational burden and copy number alterations associated with different melanoma subtypes. The significance of the mutated BRAF gene and its pathway, notably BRAFV600 variants, in melanoma is paramount. BRAF mutations, prevalent across diverse cancer types, present therapeutic avenues, with clinical trials validating the efficacy of targeted therapies and immunotherapy. Additional driver mutations in oncogenes further characterize specific melanoma pathways, impacting tumor behavior. While histopathological examination remains pivotal, challenges persist in molecularly classifying melanocytic tumors. In this review, we went through all molecular characterization that aid in discriminating common and ambiguous lesions. Integration of highly sensitive molecular diagnostic tests into the diagnostic workflow becomes indispensable, particularly in instances where histology alone fails to achieve a conclusive diagnosis. A diagnostic algorithm based on different molecular features inferred by the various studies is here proposed.

Emerging strategies to treat rare and intractable subtypes of melanoma

Melanoma is the deadliest form of skin cancer, possessing a diverse landscape of subtypes with distinct molecular signatures and levels of aggressiveness. Although immense progress has been achieved therapeutically for patients with the most common forms of this disease, little is known of how to effectively treat patients with rarer subtypes of melanoma. These subtypes include acral lentiginous (the rarest form of cutaneous melanoma; AL), uveal, and mucosal melanomas, which display variations in distribution across (a) the world, (b) patient age-groups, and (c) anatomic sites. Unfortunately, patients with these relatively rare subtypes of melanoma typically respond worse to therapies approved for the more common, non-AL cutaneous melanoma and do not have effective alternatives, and thus consequently have worse overall survival rates. Achieving durable therapeutic responses in these high-risk melanoma subtypes represents one of the greatest challenges of the field. This review aims to collate and highlight effective preclinical and/or clinical strategies against these rare forms of melanoma.

Differential Expression of Cancer Testis Antigens on Lentigo Maligna and Lentigo Maligna Melanoma

The cancer/testis antigens (CTA) are a group of antigens expressed on germ cells of healthy testis and malignant tumors. We studied whether CTA are present on lentigo maligna (LM) and LM melanoma (LMM) samples. Immunohistochemical expression of a panel of CTA (MAGE-A1, A2- A3, NY-ESO-1, PRAME, SSX-2, and a MAGE-A antibody reactive with -A1, -A2, -A3, -A4, -A6, -A10, and -A12) was investigated in formalin-fixed paraffin-embedded samples from LMM (n = 20), LM (n = 8), chronically sun-exposed skin (n = 7), and healthy skin (n = 7). In 4 LMM lesions, the MAGE-A marker was positive. Another 3 LMM lesions were positive for MAGE-A1, MAGE-A2, and MAGE-A3. PRAME was positive in 18/20 LMM and 6/8 LM. We did not find expression of MAGE, NY-ESO-1, or SSX-2 in LM, thereby excluding these CTA as diagnostic markers to discern malignant melanocytes in LM from normal melanocytes. LMM did express MAGE, NY-ESO-1, and SSX-2. If a biopsy from a lesion suspect for LM shows positivity for MAGE, NY-ESO-1, and SSX-2, the lesion may actually be LMM. In contrast, PRAME expression was found in LM at low levels and in LMM at much higher levels, and absent in normal melanocytes. PRAME can potentially be used to discern normal melanocytes from malignant melanocytes.

Tumor genetic heterogeneity analysis of chronic sun-damaged melanoma

Chronic sun‐damaged (CSD) melanoma represents 10%–20% of cutaneous melanomas and is characterized by infrequent BRAF V600E mutations and high mutational load. However, the order of genetic events or the extent of intra‐tumor heterogeneity (ITH) in CSD^high melanoma is still unknown. Ultra‐deep targeted sequencing of 40 cancer‐associated genes was performed in 72 in situ or invasive CMM, including 23 CSD^high cases. In addition, we performed whole exome and RNA sequencing on multiple regions of primary tumor and multiple in‐transit metastases from one CSD^high melanoma patient. We found no significant difference in mutation frequency in melanoma‐related genes or in mutational load between in situ and invasive CSD^high lesions, while this difference was observed in CSD^low lesions. In addition, increased frequency of BRAF V600K, NF1, and TP53 mutations (p < .01, Fisher's exact test) was found in CSD^high melanomas. Sequencing of multiple specimens from one CSD^high patient revealed strikingly limited ITH with >95% shared mutations. Our results provide evidence that CSD^high and CSD^low melanomas are distinct molecular entities that progress via different genetic routes.

Histologic Features Associated With an Invasive Component in Lentigo Maligna Lesions

Importance

Lentigo maligna (LM) presents an invasive component in up to 20% of biopsied cases, but to date the histologic features useful in detecting this invasive component have not been described. Some histologic characteristics are hypothesized to contribute to the progression of LM invasion.

Objective

To identify the histologic characteristics associated with lentigo maligna melanoma (LMM) in patients with LM diagnosed by a partial diagnostic biopsy.

Design, Setting, and Participants

A retrospective cross-sectional study of patients treated between January 1, 2000, and December 31, 2017, was conducted in a referral oncology center in València, Spain. Data and specimens of patients (n = 96) with a diagnosis of primary cutaneous melanoma in the form of either LM or LMM who had undergone surgical treatment, a complete histologic examination of the whole tumor, and an initial diagnostic partial biopsy of LM were included in the study. Histologic assessment was blinded to the presence of an invasive component.

Interventions

All biopsy specimens were evaluated for the presence of certain histologic characteristics.

Main Outcomes and Measures

Comparisons between invasive samples and samples without an invasive component were performed. The differences in the distribution of variables between the groups were assessed using the χ2 and Fisher exact tests, and the degree of association of the relevant variables was quantified by logistic regression models. A classification and regression tree analysis was performed to rank the variables by importance.

Results

In total, 96 patients had sufficient histologic material that could be evaluated. The patients were predominantly male (56 [58.3%]) and had a mean (SD) age at diagnosis of 72 (12) years. Of these patients, 63 (65.6%) had an LM diagnosis and 33 (34.4%) had an LMM diagnosis (an invasive component). The histologic variables associated with the presence of an invasive component were melanocytes forming rows (odds ratio [OR], 11.5; 95% CI, 1.4-94.1; P = .02), subepidermal clefts (OR, 2.8; 95% CI, 1.0-7.9; P = .049), nests (OR, 3.0; 95% CI, 1.1-8.6; P = .04), and a lesser degree of solar elastosis (OR, 0.4; 95% CI, 0.1-1.1; P = .07). A classification and regression tree analysis of the relevant histologic features was able to accurately identify lentigo maligna with an invasive component (LMM) in more than 60% of patients.

Conclusions and Relevance

These findings may be useful in classifying early LM specimens at higher risk of invasion, which may eventually be relevant in identifying the most appropriate management for LM.

Putative genomic characteristics of BRAF V600K versus V600E cutaneous melanoma

Approximately 50% of all cutaneous melanomas harbor activating BRAF V600 mutations; among, these 10-30% carry the V600K mutation. Clinically, patients with V600K tumors experience distant metastases sooner and have an increased risk of relapse and shorter survival than patients with V600E tumors. Despite the clinical and other histopathological differences between these BRAF tumor subtypes, little is known about them at the genomic level. Herein, we systematically compared BRAF V600E and V600K skin cutaneous melanoma (SKCM) samples from the Cancer Genome Atlas (TCGA) for differential protein, gene, and microRNA expression genome-wide using the Mann-Whitney U-test. Our analyses showed that elements of energy-metabolism and protein-translation pathways were upregulated and that proapoptotic pathways were downregulated in V600K tumors compared with V600E tumors. We found that c-Kit protein and KIT gene expressions were significantly higher in V600K tumors than in V600E tumors, concurrent with significant downregulation of several KIT-targeting microRNAs (mir) including mir-222 in V600K tumors, suggesting KIT and mir-222 might be key genomic contributors toward the clinical differences observed. The relationship that we uncovered among KIT/c-Kit expression, mir-222 expression, and growth and prosurvival signals in V600 tumors is intriguing. We believe that the observed clinical aggressiveness of V600K tumors compared to V600E tumors may be attributable to the increased energy metabolism, protein translation and prosurvival signals compared with V600E tumors. If confirmed using larger numbers of V600K tumors, our results may prove useful for designing clinical management and targeted chemotherapeutical interventions for BRAF V600K-positive melanomas. Finally, the small sample size in V600K tumors is a major limitation of our study.

Systemic BRAF/MEK Inhibitors as a Potential Treatment Option in Metastatic Conjunctival Melanoma

AIM

In this review, we outline similarities between conjunctival and skin melanoma as well as the effectiveness of combined BRAF/MEK inhibition in melanoma, and discuss the applicability of these agents in conjunctival melanoma.

METHODS

The study provides a PubMed literature review.

RESULTS

Conjunctival melanoma and skin melanoma are genetically and phenotypically related. Both tumors typically harbor BRAF mutations in more than 50% of cases. New targeted therapies in metastatic skin melanoma include selective inhibition of BRAF and MEK. Combined BRAF/MEK inhibition has revolutionized the treatment of metastatic skin melanoma, significantly improving patients' prognoses. While these new substances have been investigated extensively in the treatment of skin melanoma, comparable studies in conjunctival melanoma do not exist owing to the rarity of the malignancy.

CONCLUSIONS

The application of combined BRAF/MEK inhibition in metastatic or unresectable conjunctival melanoma shows great potential for improving patients' prognoses. Future studies are needed to investigate the assumed benefit.

Targeting of the MAPK and AKT pathways in conjunctival melanoma shows potential synergy

PURPOSE

Conjunctival melanoma (CM) is a rare but lethal form of cancer. Similar to cutaneous melanoma, CM frequently carries activating mutations in BRAF and NRAS. We studied whether CM as well as conjunctival benign and premalignant melanocytic lesions express targets in the mitogen-activated protein kinase (MAPK) and AKT pathways, and whether specific inhibitors can suppress CM growth in vitro.

METHODS

131 conjunctival lesions obtained from 129 patients were collected. The presence of BRAF V600E mutation and expression of phosphorylated (p)-ERK and p-AKT were assessed by immunohistochemistry. We studied cell proliferation, phosphorylation, cell cycling and apoptosis in three CM cell lines using two BRAF inhibitors (Vemurafenib and Dabrafenib), a MEK inhibitor (MEK162) and an AKT inhibitor (MK2206).

RESULTS

The BRAF V600E mutation was present in 19% of nevi and 26% of melanomas, but not in primary acquired melanosis (PAM). Nuclear and cytoplasmic p-ERK and p-AKT were expressed in all conjunctival lesions. Both BRAF inhibitors suppressed growth of both BRAF mutant CM cell lines, but only one induced cell death. MEK162 and MK2206 inhibited proliferation of CM cells in a dose-dependent manner, and the combination of these two drugs led to synergistic growth inhibition and cell death in all CM cell lines.

CONCLUSION

ERK and AKT are constitutively activated in conjunctival nevi, PAM and melanoma. While BRAF inhibitors prohibited cell growth, they were not always cytotoxic. Combining MEK and AKT inhibitors led to more growth inhibition and cell death in CM cells. The combination may benefit patients suffering from metastatic conjunctival melanoma.

Guanine nucleotide exchange factor H1 can be a new biomarker of melanoma

Guanine nucleotide exchange factor H1 (GEF-H1), which couples microtubule dynamics to RhoA activation, is a microtubule-regulated exchange factor. Studies have shown that GEF-H1 can be involved in various cancer pathways; however, the clinical significance of GEF-H1 expression and functions in melanoma has not been established. In this study, we investigated the relationship between clinical outcomes and GEF-H1 functions in melanoma. A total of 60 cases of different grades of melanoma samples were used to detect the expression of GEF-H1. Results showed that both messenger RNA and protein levels of GEF-H1 were significantly higher in high-grade melanomas. Furthermore, patients with high GEF-H1 expression had a shorter overall survival (22 months) than patients with low level of GEF-H1 expression (33.38 months). We also found that GEF-H1 can promote the proliferation and metastasis of melanoma cells. In summary, these results suggested that GEF-H1 may be a valuable biomarker for assessing the degree and prognosis of melanoma following surgery.

From melanocytes to melanomas

Melanomas on sun-exposed skin are heterogeneous tumours, which can be subtyped on the basis of their cumulative levels of exposure to ultraviolet (UV) radiation. A melanocytic neoplasm can also be staged by how far it has progressed, ranging from a benign neoplasm, such as a naevus, to a malignant neoplasm, such as a metastatic melanoma. Each subtype of melanoma can evolve through distinct evolutionary trajectories, passing through (or sometimes skipping over) various stages of transformation. This Review delineates several of the more common progression trajectories that occur in the patient setting and proposes models for tumour evolution that integrate genetic, histopathological, clinical and biological insights from the melanoma literature.

Melanoma Epidemiology and Prevention

The epidemiology of melanoma is complex, and individual risk depends on sun exposure, host factors, and genetic factors, and in their interactions as well. Sun exposure can be classified as intermittent, chronic, or cumulative (overall) exposure, and each appears to have a different effect on type of melanoma. Other environmental factors, such as chemical exposures-either through occupation, atmosphere, or food-may increase risk for melanoma, and this area warrants further study. Host factors that are well known to be important are the numbers and types of nevi and the skin phenotype. Genetic factors are classified as high-penetrant genes, moderate-risk genes, or low-risk genetic polymorphisms. Subtypes of tumors, such as BRAF-mutated tumors, have different risk factors as well as different therapies. Prevention of melanoma has been attempted using various strategies in specific subpopulations, but to date optimal interventions to reduce incidence have not emerged.

Lentigo maligna and lentigo maligna melanoma: contemporary issues in diagnosis and management

Lentigo maligna and lentigo maligna melanomas present diagnostic and treatment dilemmas due to their frequent presence within a background of sun-damaged skin, and their location on cosmetically and functionally sensitive areas. As the incidence of this entity is increasing, diagnostic and management controversies have developed. While surgery remains the gold standard of treatment, nonsurgical treatment options are also emerging for both adjunctive and primary therapy.