Recent advances in cutaneous melanoma: towards a molecular model and targeted treatment

Melanoma is an aggressive disease process, with a heterogeneous aetiology linked to environmental and genetic risk factor profiles. Overall prognosis for advanced disease remains poor, and a lack of effective systemic therapies has prompted investigation into alternative strategies. The identification of novel mutations that instigate and perpetuate melanocyte transformation has offered insight into new treatment approaches, and the subsequent development of targeted treatments appears to be integral to improving melanoma survival. This article reviews the mechanisms of melanoma oncogenesis and classic molecular signalling pathways, targeted treatment approaches based on the molecular model and immunotherapy, and the advent of next‐generation sequencing technologies in understanding the complexity of the melanoma pathogenome. In addition to the known somatic activating mutations BRAF and NRAS, exome sequencing has recently identified RAC1, a novel UV‐signature gain‐of‐function mutation. Germline mutations associated with familial melanoma have added a further dimension to the molecular underpinnings of melanoma, implicating BAP1 and MITF as melanoma predisposition genes. Advances in understanding melanoma and implementing targeted treatment strategies will be of increasing importance in this era of personalised medicine.     

Update on the clinical use of kinase inhibitors in melanoma

The identification of targetable molecules in cellular signaling pathways represents a milestone in the treatment of melanoma. Selective inhibitors of these molecules, known as phosphokinases, allow for individual signaling pathways to be “switched off”. This is of particular importance for tumors in which these pathways are constitutively activated by mutations in genes encoding said molecules. Especially patients with BRAF‐mutated melanomas significantly benefit from kinase inhibitor therapies, with the current standard of combined BRAF and MEK inhibition providing very good long‐term disease control. Such regimens have been shown to achieve a progression‐free survival of more than ten months and an overall survival of more than two years, along with good quality of life. Given that the majority of patients develop secondary resistance during long‐term kinase inhibitor therapy, current clinical trials are geared towards finding suitable drug combinations including inhibitors of other signaling pathways as well as immune checkpoint inhibitors. The present review highlights targeted therapies for melanoma currently available as well as potential future options presently under clinical investigation.     

Targeted therapy in melanoma

Since the discovery of activating mutations in the BRAF oncogene in melanoma, there has been remarkable progress in the development of targeted therapies for unresectable and metastatic melanoma. We review the latest developments in our understanding of the role of BRAF/MEK/ERK pathway signaling in melanoma, and the development of inhibitors of this pathway. We also explore alternative mutations seen in melanoma, such as NRAS, KIT, GNAQ, and GNA11, and the drug development that is ongoing based on this biology. Strategies for the management of the vexing clinical problem of BRAF inhibitor resistance, primarily via combination therapy, are outlined. With the recent approval of the BRAF inhibitor vemurafenib for stage IV metastatic melanoma, use of this agent is expanding in the United States. Thus, management of the skin toxicities of this agent, such as squamous cell carcinomas, “acneiform” eruptions, hand-foot syndrome, and panniculitis, will be a growing problem facing dermatologists today. We discuss the toxicities of targeted agents in use for melanoma, in particular the dermatologic effects and the management of these skin toxicities.     

New developments in dermatological oncogenetics

Activated intracellular signaling pathways based on mutations in oncogenes and tumor suppressor genes play an important role in a variety of malignant tumors. In dermatology, such mutations have been identified in melanoma, basal cell carcinoma and squamous cell carcinoma. These have partly led to the establishment of new, targeted therapies. Treatment successes have been particularly impressive for melanoma with small molecule inhibitors directed against the mutated BRAF oncogene and in basal cell carcinoma with inhibitors directed against the hedgehog signaling pathway. New sequencing technologies, in particular next generation sequencing, have led to a better and more comprehensive understanding of malignant tumors. This approach confirmed the pathogenic role of BRAF, NRAS and MAP kinase pathways for melanoma. At the same time, a series of further interesting target molecules with oncogenic mutations such as ERBB4, GRIN2A, GRM3, PREX2, RAC1 and TP53 were identified. New aspects have recently been shown for squamous cell carcinoma by detection of mutations in the NOTCH signaling pathway. A better understanding of the pathogenesis of these and other tumors should lead to improved and maybe even individualized treatment. The current developments in dermatological oncogenetics based on the new sequencing technologies are reviewed.     

A new approach to the diagnosis and study of Malassezia infections

Melanoma is one of the most aggressive and deadly skin cancers, and, in its advanced stages, accounts for > 80% mortality. The incidence of melanoma is increasing worldwide; however, beyond surgical removal of the tumour, there is currently no curative therapy available, especially for its advanced stages. This may, in part, be owing to incomplete understanding of the molecular mechanisms that regulate the initiation and/or progression of melanoma to metastasis. The molecular mechanisms leading to the development and progression of melanoma are the focus of intense investigation, and many genetic/epigenetic alterations affecting melanoma progression and development have been identified. microRNAs (miRNAs) are emerging as important causal modulators in the development and progression of melanoma. The understanding of miRNA‐mediated regulation of tumours has grown immensely over the last few years, as it has been understood to regulate most biological processes. Here, we review the currently available data on miRNAs associated with melanoma, highlighting those deregulated miRNAs that target important genes and pathways involved in the progression of melanocytes to primary and metastatic melanoma. We also review their potential clinical utility as biomarkers and potential use in targeted therapy.     

Liquid biopsy to monitor melanoma patients

During the last six years, several innovative, systemic therapies for the treatment of metastatic malignant melanoma (MM) have emerged. Conventional chemotherapy has been superseded by novel first‐line therapies, including systemic immunotherapies (anti‐CTLA4 and anti‐PD1; authorization of anti‐PDL1 is anticipated) and therapies targeting specific mutations (BRAF, NRAS, and c‐KIT). Thus, treating physicians are confronted with new challenges, such as stratifying patients for appropriate treatments and monitoring long‐term responders for progression. Consequently, reliable methods for monitoring disease progression or treatment resistance are necessary. Localized and advanced cancers may generate circulating tumor cells and circulating tumor DNA (ctDNA) that can be detected and quantified from peripheral blood samples (liquid biopsy). For melanoma patients, liquid biopsy results may be useful as novel predictive biomarkers to guide therapeutic decisions, particularly in the context of mutation‐based targeted therapies. The challenges of using liquid biopsy include strict criteria for the phenotypic nature of circulating MM cells or their fragments and the instability of ctDNA in blood. The limitations of liquid biopsy in routine diagnostic testing are discussed in this review.     

Melanoma genetics and therapeutic approaches in the 21st century: moving from the benchside to the bedside

Metastatic melanoma is notoriously one of the most difficult cancers to treat. Although many therapeutic regimens have been tested, very few achieve response rates greater than 25%. Given the rising incidence of melanoma and the paucity of effective treatments, there is much hope and excitement in leveraging recent genetic and molecular insights for therapeutic advantage. Over the past 30 years, elegant studies by many groups have helped decipher the complex genetic networks involved in melanoma proliferation, progression and survival, as well as several genes involved in melanocyte development and survival. Many of these oncogenic loci and pathways have become crucial targets for pharmacological development. In this article we review: (1) our current understanding of melanoma genetics within the context of signaling networks; (2) targeted therapies, including an extensive discussion of promising agents that act in the Bcl-2 signaling network; (3) future areas of research.     

Assessment of clinical parameters associated with mutational status in metastatic malignant melanoma: a single‐centre investigation of 141 patients

Background Inhibitors of the mutated, constitutively activated BRAF protein have shown efficacy in the treatment of metastatic melanoma in clinical trials. Mutation analysis especially of the BRAF, NRAS and KIT genes is essential to identify patients suitable for targeted therapies and has been introduced into routine patient care. Objectives To correlate mutational status with clinical parameters including age, skin type, number of melanocytic naevi, primary tumour location, chronic sun damage and exposure to ultraviolet (UV) irradiation. The overall aim was to define subgroups with an increased or decreased likelihood of gene mutations. Additionally, the impact of activating BRAF mutations on clinical course was investigated. Methods In a single‐centre, retrospective approach, mutation analysis was performed on patients with metastatic malignant melanoma. Clinical parameters were correlated with molecular findings. The total sun‐burden score was assessed using a validated standardized questionnaire. Results The analysis included 141 patients with metastatic melanoma. Forty‐four per cent of patients had activating BRAF mutations and were significantly younger than patients with wild‐type BRAF or with NRAS mutations. KIT mutations were detected in only 3% of the patients. BRAF‐mutated melanomas developed preferentially in intermittently sun‐exposed areas of the body, and patients had significantly more melanocytic naevi. Once patients had progressed into stage IV disease, survival times were identical for those with BRAF‐mutated and BRAF wild‐type tumours. Conclusions Mutations of the BRAF gene are correlated with younger age, a higher number of melanocytic naevi and a tumour location in intermittently UV‐exposed skin. Signs of chronic photodamage are not indicative of mutational status. Patients with metastatic melanoma with BRAF mutations showed a nonsignificant tendency to progress later to stage IV disease, but once metastases were present the prognosis was identical to that with BRAF wild‐type tumours.     

Trends in the prognosis of metastatic melanoma in the era of targeted therapy and immunotherapy: A single‐institution survey in Japan

Advances in anticancer therapy, including the development of targeted therapy and immunotherapy, have drastically changed treatment options for metastatic melanoma. However, to date, only a few studies have been published that directly compare overall survival (OS) before and after introduction of these new therapeutic options in Japan. We retrospectively surveyed patients with metastatic melanoma treated in our hospital between 1989 and 2019 to investigate the OS benefit of the new therapies. A total of 115 patients with metastatic melanoma (cutaneous origin, 92; mucosal, 14; uveal, two) were included in the study. Kaplan–Meier analysis showed that the patient group receiving targeted therapy/immunotherapy (TT/IT) (n = 47) had a median OS of 19.0 months, which was longer than that in patients receiving conventional chemotherapy (n = 42, 8.0 months) or no treatment (n = 26, 6.0 months) (P < 0.001). In the subgroup analysis performed for the TT/IT group, patients of younger age and with the BRAF mutation had significantly improved OS. As the number of treatment lines increased, the median OS tended to become longer. Our real‐world data confirmed an improvement of median OS upon the introduction of the new therapies for metastatic melanoma. However, the long‐term OS benefit was limited, possibly because of racial differences in some of the clinical characteristics. To improve the overall melanoma prognosis, the entire treatment strategy, including perioperative therapy needs strengthening.     

KIT as an Oncogenic Driver in Melanoma: An Update on Clinical Development

Metastatic melanoma is a heterogenous disease that has served as a model for the development of both targeted therapy and immunotherapy. KIT-mutated melanoma represents a rare subset, most commonly arising from acral, mucosal, and chronically sun-damaged skin. Additionally, KIT alterations are enriched in the triple wild-type subtype of cutaneous melanoma. Activating alterations of KIT—a transmembrane receptor tyrosine kinase important for cell development, growth, and differentiation—have been shown to be critical to oncogenesis across many tumor subtypes. Following the successes of BRAF-targeted therapy in melanoma and KIT-targeted therapy in gastrointestinal stromal tumors, small-molecule tyrosine kinase inhibitors targeting KIT have been examined in KIT-mutated melanoma. KIT inhibitors that have been investigated in relevant clinical trials in advanced melanoma include imatinib, sunitinib, dasatinib, and nilotinib. In these studies, selected patients with KIT-mutated melanoma were shown to be responsive to therapy with KIT inhibition, especially patients with L576P and K642E mutations. This has led to the incorporation of KIT-targeted therapy in the National Comprehensive Cancer Network guidelines for systemic therapy for metastatic or unresectable melanoma. Current research and development efforts include novel KIT-targeted therapies and testing KIT inhibitors in combination with immunotherapy.

     

Vitiligo and melanoma‐associated hypopigmentation (MAH):shared and discriminative features

Background: It is unclear if differences between melanoma‐associated hypopigmentation (MAH) and classical vitiligo exist. Patients and Methods: Hypopigmented areas and associated lesions (halo nevi, hypopigmented scars) in 15 melanoma patients and 31 patients with classical vitiligo were analyzed by digital photography. The activity of the respective lesions was assessed by the vitiligo disease activity (VIDA) score.Associated diseases were recorded by history and serological tests;genotyping of HLA class I antigens as well as histology/immunohistology were performed. Results: MAH were diagnosed in 12 of 15 melanoma patients;mean onset was 4.8 years after the primary diagnosis of the melanoma. Three melanoma patients reported hypopigmentation more than 15 years before diagnosis of melanoma. In the history and family history of vitiligo patients, autoimmune diseases were much more frequent and haplotype HLA‐A2 was twice as common compared to MAH patients.MAH lesions were most often distributed in a bilateral symmetrical pattern,corresponding to vitiligo.MAH was less progressive compared to classical vitiligo;however,it was more often associated with other acquired leukodermas. In both groups hypopigmentation spread centripetally to the trunk. Histological and immunohistological differences were not found. Conclusions: Whereas differences exist concerning associated autoimmune dis‐eases,MAH and vitiligo shared many common clinical and histological features. Further studies are needed to assess the clinical relevance of vitiligo‐like alterations in melanoma patients.     

Optimal Management of Metastatic Melanoma: Current Strategies and Future Directions

Melanoma is increasing in incidence and remains a major public health threat. Although the disease may be curable when identified early, advanced melanoma is characterized by widespread metastatic disease and a median survival of less than 10 months. In recent years, however, major advances in our understanding of the molecular nature of melanoma and the interaction of melanoma cells with the immune system have resulted in several new therapeutic strategies that are showing significant clinical benefit. Current therapeutic approaches include surgical resection of metastatic disease, chemotherapy, immunotherapy, and targeted therapy. Dacarbazine, interleukin-2, ipilimumab, and vemurafenib are now approved for the treatment of advanced melanoma. In addition, new combination chemotherapy regimens, monoclonal antibodies blocking the programmed death-1 (PD-1)/PD-ligand 1 pathway, and targeted therapy against CKIT, mitogen-activated protein/extracellular signal-regulated kinase (MEK), and other putative signaling pathways in melanoma are beginning to show promise in early-phase clinical trials. Further research on these modalities alone and in combination will likely be the focus of future clinical investigation and may impact the outcomes for patients with advanced melanoma.     

The novel PI3 kinase inhibitor,BAY 80‐6946, impairs melanoma growth in vivo and in vitro

Due to its almost universal resistance to chemotherapy, metastasized melanoma remains a major challenge in clinical oncology. Given that phosphatidyl inositol‐3 kinase (PI3K) activation in melanoma cells is associated with poor prognosis, disease progression and resistance to chemotherapy, the PI3K‐Akt signalling pathway is a promising therapeutic target for melanoma treatment. We analysed six human melanoma cell lines for their constitutive activation of Akt and then tested two representative lines, A375 and LOX, for their susceptibility to PI3K‐inhibition by the highly specific small molecule inhibitor, BAY 80‐6946. In addition, the effect of BAY 80‐6946 on A375 and LOX melanoma cells was assessed in vivo in a xenotransplantation mouse model. We provide experimental evidence that specifically inhibiting the PI3K pathway and phosphorylation of Akt by this novel compound results in antitumoral activities including inhibition of proliferation, induction of apoptosis and cell cycle arrest in vitro and in vivo. However, the susceptibility did not show a clear‐cut pattern and differed between the melanoma cell lines tested, resulting in in vivo growth inhibition of A375 but not LOX melanoma cells. Thus, in some cases BAY 80‐6946 or related compounds may be a valuable addition to the therapeutic armamentarium.     

Molecular markers in melanoma

The last few years have witnessed the dawn of the molecular era in melanoma treatment. With the advent of successful therapy targeting mutant BRAF, melanoma is leading the field of cancer research in the molecular approach to therapy of advanced disease. Attempting to keep pace with advances in therapy are advances in the molecular assessment of melanoma progression, facilitated by the availability of genome‐wide approaches to interrogate the malignant phenotype. At the DNA level, this has included approaches such as comparative genomic hybridization. At the RNA level, this has consisted of gene expression profiling using various assay methodologies. In certain instances, markers identified using these platforms have been further examined and developed using fluorescence in situ hybridization and immunohistochemical analysis. In this article, we will review recent progress in the development of novel molecular markers for melanoma that are nearing clinical application. We will review developments in the molecular classification of melanoma, in the molecular diagnosis of melanoma, and in the molecular assessment of melanoma prognosis.     

Aberrant hypermethylation in primary tumours and sentinel lymph node metastases in paediatric patients with cutaneous melanoma

Background Debate on how to manage paediatric patients with cutaneous melanoma continues, particularly in those with sentinel lymph node (SLN) metastases who are at higher risk of poor outcomes. Management is often based on adult algorithms, although differences in clinical outcomes between paediatric and adult patients suggest that melanoma in paediatric patients differs biologically. Yet, there are no molecular prognostic studies identifying these differences. Objectives We investigated the epigenetic (methylation) regulation of several tumour‐related genes (TRGs) known to be significant in adult melanoma progression in histopathology(+) SLN metastases (n = 17) and primary tumours (n = 20) of paediatric patients with melanoma to determine their clinical relevance. Methods Paediatric patients (n = 37; ≤ 21 years at diagnosis) with American Joint Committee on Cancer stage I–III cutaneous melanoma were analysed. Gene promoter methylation of the TRGs RASSF1A, RARβ2, WIF1 and APC was evaluated. Results Hypermethylation of RASSF1A, RARβ2, WIF1 and APC was found in 29% (5/17), 25% (4/16), 25% (4/16) and 19% (3/16) of histopathology(+) SLNs, respectively. When matched to adult cutaneous melanomas by Breslow thickness and ulceration, hypermethylation of all four TRGs in SLN(+) paediatric patients with melanoma was equivalent to or less than in adults. With a median follow‐up of 55 months, SLN(+) paediatric patients with melanoma with hypermethylation of > 1 TRG vs. ≤ 1 TRG had worse disease‐free (P = 0·02) and overall survival (P = 0·02). Conclusions Differences in the methylation status of these TRGs in SLN(+) paediatric and adult patients with melanoma may account for why SLN(+) paediatric patients have different clinical outcomes. SLN biopsy should continue to be performed; within SLN(+) paediatric patients with melanoma, hypermethylation of TRGs can be used to identify a subpopulation at highest risk for poor outcomes who warrant vigilant clinical follow‐up.     

Highly pigmented Tg(Grm1) mouse melanoma develops non‐pigmented melanoma cells in distant metastases

Murine model systems are critically required tools for the investigation of unknown mechanisms of melanoma development and metastasis and for developing more efficient therapies. The Tg(Grm1)EPv melanoma mouse model is characterized by spontaneous development of pigmented cutaneous melanomas at hairless skin regions, with a short latency and 100% penetrance. Local metastasis was described in initial analyses; however, melanoma cells were not observed in distant organs. Here, we demonstrate that the established Tg(Grm1)EPv melanoma mouse model exhibits more extensive metastasis into distant organs than previously described. Disseminated cells undergo phenotypic changes, as we observed high numbers of non‐pigmented Grm1‐expressing melanoma cells within distant organs. As such changes during metastasis are common in human melanoma, our findings demonstrate that this mouse model represents an even more useful tool to study unknown mechanisms of metastasis in human melanoma than previously assumed.     

Usefulness of serum 5‐S‐cysteinyl‐dopa as a biomarker for predicting prognosis and detecting relapse in patients with advanced stage malignant melanoma

With the recent development of novel molecular targeted drugs for advanced stage malignant melanoma (MM), including RAF and mitogen‐activated protein kinase kinase inhibitors and immune checkpoint blockers, the early detection of relapse is important for managing patients with MM. In this study, we retrospectively analyzed two conventional serum biomarkers, 5‐S‐cysteinyl‐dopa and lactate dehydrogenase, in patients with MM (n = 140) who were treated at a single Japanese institute from June 2007 to June 2015. At the initial hospital visit, serum 5‐S‐cysteinyl‐dopa levels were significantly increased in patients with stages III (n = 38) and IV (n = 20) MM compared with patients with stages 0–II (n = 62) MM. In addition, in patients with stages III and IV MM, serum 5‐S‐cysteinyl‐dopa levels of more than 15.0 nmol/L at initial hospital visit correlated with a poor prognosis. In 11 of 14 patients whose disease progressed during follow up (mostly from stages III–IV), serum 5‐S‐cysteinyl‐dopa levels exceeded the normal limit of 10.0 nmol/L during the clinical detection of distant metastases. These results indicate the usefulness of measuring serum 5‐S‐cysteinyl‐dopa levels at initial hospital visit and during follow up for early and effective therapeutic interventions using newly developed molecular targeted drugs.     

Tumorimmunabwehr und Autoimmunität: Erkenntnisse für die Entwicklung moderner Melanomvakzinen aus tierexperimentellen Studien

Summary: Some patients with advanced melanoma benefit from non‐specific immunotherapy. The molecular identification of melanoma antigens allows for the development of specific vaccines. Animal studies allow for insights into the possibility to generate and maintain immunity against melanoma antigens. It has become clear that the stimulation of melanoma‐specific T cells is limited by mechanisms responsible for peripheral immune tolerance. Novel genetic vaccine strategies are able to circumvent immune tolerance in laboratory mice. This requires the adjuvant application of dendritic cells or the fusion of the antigen‐encoding cDNA with immunostimulatory proteins. Additionally, melanoma‐specific T cells have to be attracted into the tumor tissue with the help of proinflammatory signals in a therapeutic setting. We believe that these lessons learned in the murine system are of great importance for the future development of melanoma vaccines for application in man.     

BRAF mutation testing algorithm for vemurafenib treatment in melanoma: recommendations from an expert panel

The incidence of melanoma has increased rapidly over the past 30 years, and the disease is now the sixth most common cancer among men and women in the U.K. Many patients are diagnosed with or develop metastatic disease, and survival is substantially reduced in these patients. Mutations in the BRAF gene have been identified as key drivers of melanoma cells and are found in around 50% of cutaneous melanomas. Vemurafenib (Zelboraf^®; Roche Molecular Systems Inc., Pleasanton, CA, U.S.A.) is the first licensed inhibitor of mutated BRAF, and offers a new first‐line option for patients with unresectable or metastatic melanoma who harbour BRAF mutations. Vemurafenib was developed in conjunction with a companion diagnostic, the cobas^® 4800 BRAF V600 Mutation Test. The purpose of this paper is to make evidence‐based recommendations to facilitate the implementation of BRAF mutation testing and targeted therapy in patients with metastatic melanoma in the U.K. The recommendations are the result of a meeting of an expert panel and have been reviewed by melanoma specialists and representatives of the National Cancer Research Network Clinical Study Group on behalf of the wider melanoma community. This article is intended to be a starting point for practical advice and recommendations, which will no doubt be updated as we gain further experience in personalizing therapy for patients with melanoma.