Update on Molecular Pathology of Cutaneous Melanocytic Lesions: What is New in Diagnosis and Molecular Testing for Treatment?

Neurocutaneous melanosis presenting with hydrocephalus and malignant transformation: case-based update

INTRODUCTION

Neurocutaneous melanosis (NCM) is a sporadic condition characterised by congenital melanocytic nevi and melanocytic thickening of the leptomeninges. It is believed to result from congenital dysplasia of melanin-producing cells within the skin and leptomeninges. The management of cutaneous manifestations remains controversial; for neurological manifestations, outcome remains poor even with the use of radiotherapy and chemotherapy.

PATIENTS AND METHODS

We describe the case of a 5-month-old boy who presented with giant congenital melanocytic nevus and hydrocephalus. MR imaging and CSF immunohistochemistry confirmed leptomeningeal melanosis. We discuss the diagnosis, treatment and prognosis of this rare disorder in the light of recent published literature.

RESULTS

Patient required placement of right-sided ventriculoperitoneal shunt to control hydrocephalus. The patient tolerated the procedure well and was discharged home with normal neurological function. A presumptive diagnosis of NCM was made based on the MR characteristics, CSF cytology and clinical presentation. He received trametinib, a MAPK/Erk kinase inhibitor for 7 months. At 30 months of age, he developed left-sided weakness and status epilepticus requiring paediatric intensive care unit admission and ventilator support. The patient eventually succumbed to malignant transformation of leptomeningeal disease.

CONCLUSION

Cutaneous manifestations of NCM are usually congenital, and neurological manifestations develop early in life. Patients with large or multiple congenital nevi should therefore be investigated early to facilitate treatment. MR imaging is the investigation of choice which can further assist in performing biopsy. Symptomatic NCM is refractory to radiotherapy and chemotherapy and has a poor prognosis. A multidisciplinary approach is necessary in the management of NCM patients.

The next generation of metastatic melanoma: uncovering the genetic variants for anti-BRAF therapy response

Metastatic melanoma (MM) is a highly aggressive cancer with a median overall survival of 6-9 months, notwithstanding the numerous efforts in development of new therapeutic approaches. To this aim we tested the clinical applicability of the Ion Torrent Personal Genome Machine to simultaneously screen MM patients in order to individuate new or already known SNPs and mutations able to predict the duration of response to BRAF inhibitors. An Ampliseq Custom Panel, including 11 crucial full length genes involved in melanoma carcinogenesis and therapy response pathways, was created and used to analyze 25 MM patients. We reported BRAFV600 and NRASQ61 mutations in 68% and 24% of samples, respectively. Moreover, we more frequently identified the following alterations related to BRAF status: PIK3CAI391M (44%) and KITD737N (36%) mutations, CTLA4T17A (52%), MC1RV60L (32%) and MITFS473A (60%) polymorphisms. Considering the progression free survival (PFS), statistical analyses showed that BRAFV600 patients without any of these more frequent alterations had a higher median PFS. Protein structure changes seem to be due to these variants by in silico analysis. In conclusion, a Next-Generation Sequencing approach with custom panel may provide new information to evaluate tumor-specific therapeutic susceptibility and individual prognosis to improve the care of MM patients.

Paediatric melanoma

Paediatric melanoma, although rare, is the most common skin cancer in children. Our current knowledge on paediatric melanoma incidence trends is expanding, as several studies have addressed this issue with conflicting results. Known risk factors for paediatric melanoma include family history of melanoma, a previous history of malignancy, large congenital nevi, numerous melanocytic nevi, sunburns, increased UV exposure and a sun-sensitive phenotype. In younger children, melanoma more often presents with atypical features, such as a changing, amelanotic or uniformly coloured, often bleeding lesion, not fulfilling in most cases the conventional ABCDE criteria. The major differential diagnoses are melanocytic nevi, proliferative nodules in congenital nevi and atypical Spitz tumours. Moreover, in the younger age group non-Caucasian children are over-represented, tumours tend to be thicker and lymph nodes are often involved. Despite the frequent diagnosis at an advanced stage, the overall survival is fair in paediatric melanoma. Specific guidelines for management of melanoma in children do not exist, and most often the disease is treated similarly to melanoma in adults.

Next-generation sequencing: advances and applications in cancer diagnosis

Technological advances have led to the introduction of next-generation sequencing (NGS) platforms in cancer investigation. NGS allows massive parallel sequencing that affords maximal tumor genomic assessment. NGS approaches are different, and concern DNA and RNA analysis. DNA sequencing includes whole-genome, whole-exome, and targeted sequencing, which focuses on a selection of genes of interest for a specific disease. RNA sequencing facilitates the detection of alternative gene-spliced transcripts, posttranscriptional modifications, gene fusion, mutations/single-nucleotide polymorphisms, small and long noncoding RNAs, and changes in gene expression. Most applications are in the cancer research field, but lately NGS technology has been revolutionizing cancer molecular diagnostics, due to the many advantages it offers compared to traditional methods. There is greater knowledge on solid cancer diagnostics, and recent interest has been shown also in the field of hematologic cancer. In this review, we report the latest data on NGS diagnostic/predictive clinical applications in solid and hematologic cancers. Moreover, since the amount of NGS data produced is very large and their interpretation is very complex, we briefly discuss two bioinformatic aspects, variant-calling accuracy and copy-number variation detection, which are gaining a lot of importance in cancer-diagnostic assessment.

Genomic aberrations in spitzoid melanocytic tumours and their implications for diagnosis, prognosis and therapy

Histopathological evaluation of melanocytic tumours usually allows reliable distinction of benign melanocytic naevi from melanoma. More difficult is the histopathological classification of Spitz tumours, a heterogeneous group of tumours composed of large epithelioid or spindle-shaped melanocytes. Spitz tumours are biologically distinct from conventional melanocytic naevi and melanoma, as exemplified by their distinct patterns of genetic aberrations. Whereas common acquired naevi and melanoma often harbour BRAF mutations, NRAS mutations, or inactivation of NF1, Spitz tumours show HRAS mutations, inactivation of BAP1 (often combined with BRAF mutations), or genomic rearrangements involving the kinases ALK, ROS1, NTRK1, BRAF, RET, and MET. In Spitz naevi, which lack significant histological atypia, all of these mitogenic driver aberrations trigger rapid cell proliferation, but after an initial growth phase, various tumour suppressive mechanisms stably block further growth. In some tumours, additional genomic aberrations may abrogate various tumour suppressive mechanisms, such as cell-cycle arrest, telomere shortening, or DNA damage response. The melanocytes then start to grow in a less organised fashion and may spread to regional lymph nodes, and are termed atypical Spitz tumours. Upon acquisition of even more aberrations, which often activate additional oncogenic pathways or alter cell differentiation, the neoplastic cells become entirely malignant and may colonise and take over distant organs (spitzoid melanoma). The sequential acquisition of genomic aberrations suggests that Spitz tumours represent a continuous biological spectrum, rather than a dichotomy of benign versus malignant, and that tumours with ambiguous histological features (atypical Spitz tumours) might be best classified as low-grade melanocytic tumours. The number of genetic aberrations usually correlates with the degree of histological atypia and explains why existing ancillary genetic techniques, such as array comparative genomic hybridisation (CGH) or fluorescence in situ hybridisation (FISH), are usually capable of accurately classifying histologically benign and malignant Spitz tumours, but are not very helpful in the diagnosis of ambiguous melanocytic lesions. Nevertheless, we expect that progress in our understanding of tumour progression will refine the classification of spitzoid melanocytic tumours in the near future. By integrating clinical, pathological, and genetic criteria, distinct tumour subsets will be defined within the heterogeneous group of Spitz tumours, which will eventually lead to improvements in diagnosis, prognosis and therapy.

Primary melanocytic tumors of the central nervous system: a review with focus on molecular aspects

Primary melanocytic tumors of the central nervous system (CNS) represent a spectrum of rare tumors. They can be benign or malignant and occur in adults as well as in children, the latter often in the context of neurocutaneous melanosis. Until recently, the genetic alterations in these tumors were largely unknown. This is in contrast with cutaneous and uveal melanomas, which are known to harbor distinct oncogenic mutations that can be used as targets for treatment with small-molecule inhibitors in the advanced setting. Recently, novel insights in the molecular alterations underlying primary melanocytic tumors of the CNS were obtained, including different oncogenic mutations in tumors in adult patients (especially GNAQ, GNA11) vs. children (especially NRAS). In this review, the focus is on molecular characteristics of primary melanocytic tumors of the CNS. We summarize what is known about their genetic alterations and discuss implications for pathogenesis and differential diagnosis with other pigmented tumors in or around the CNS. Finally, new therapeutic options with targeted therapy are discussed.