Alteration of chromosome 9p21 and/or p16 in benign and dysplastic nevi suggests a role in early melanoma progression (United States)

Discrimination of Dysplastic Nevi from Common Melanocytic Nevi by Cellular and Molecular Criteria

Dysplastic nevi (DNs), also known as Clark's nevi or atypical moles, are distinguished from common melanocytic nevi by variegation in pigmentation and clinical appearance, as well as differences in tissue patterning. However, cellular and molecular differences between DNs and common melanocytic nevi are not completely understood. Using cDNA microarray, quantitative RT-PCR, and immunohistochemistry, we molecularly characterized DNs and analyzed the difference between DNs and common melanocytic nevi. A total of 111 probesets (91 annotated genes, fold change > 2.0 and false discovery rate < 0.25) were differentially expressed between the two lesions. An unexpected finding in DNs was altered differentiation and activation of epidermal keratinocytes with increased expression of hair follicle-related molecules (keratin 25, trichohyalin, ribonuclease, RNase A family, 7) and inflammation-related molecules (S100A7, S100A8) at both genomic and protein levels. The immune microenvironment of DNs was characterized by an increase of T helper type 1 (IFNγ) and T helper type 2 (IL13) cytokines as well as an upregulation of oncostatin M and CXCL1. DUSP3, which regulates cellular senescence, was identified as one of the disease discriminative genes between DNs and common melanocytic nevi by three independent statistical approaches and its altered expression was confirmed by immunohistochemistry. The molecular and cellular changes in which the epidermal-melanin unit undergoes follicular differentiation as well as upregulation of defined cytokines could drive complex immune, epidermal, and pigmentary alterations.

Immunohistochemical expression of p16 in desmoplastic melanoma

Desmoplastic melanoma can be difficult to distinguish from desmoplastic melanocytic nevi both clinically and histopathologically. Several attempts have been made to explore the use of ancillary studies to facilitate this distinction. Prior work has suggested that immunohistochemical expression of p16 could help distinguish sclerosing Spitz nevi from desmoplastic melanomas. We re-evaluated the expression of p16 in 22 desmoplastic melanomas (13 mixed and 9 pure desmoplastic tumors) and five desmoplastic melanocytic nevi (three desmoplastic Spitz nevi and two congenital melanocytic nevi with prominent dermal sclerosis). All desmoplastic melanocytic nevi were strongly immunoreactive for p16. Of the 22 desmoplastic melanomas, 6 tumors failed to label for p16, 10 were focally positive, but 6 tumors were diffusely immunoreactive. The latter finding is relevant, as it points to limitations in the diagnostic value of immunohistochemical staining for p16 for the diagnosis of desmoplastic melanocytic proliferations. Diffuse staining for p16 is not restricted to desmoplastic Spitz nevi but can also occur in a subset of desmoplastic melanomas, and this warrants caution in the use of this marker for diagnostic purposes.

The dysplastic nevus: from historical perspective to management in the modern era: part II. Molecular aspects and clinical management

The dysplastic nevus is a discreet histologic entity that exhibits some clinical and histologic features overlapping with common nevi and melanoma. These overlapping features present a therapeutic challenge, and with a lack of accepted guidelines, the management of dysplastic nevi remains a controversial subject. Although some differences between dysplastic and common nevi can be detected at the molecular level, there are currently no established markers to predict biologic behavior. In part II of this continuing medical education article, we will review the molecular aspects of dysplastic nevi and their therapeutic implications. Our goal is to provide the clinician with an up-to-date understanding of this entity to facilitate clinical management of patients with nevi that have histologic dysplasia.

Molecular biology of unreresectable meningiomas: implications for new treatments and review of the literature

Even though meningiomas are most often benign tumors, they can be locally invasive and can develop in locations that prevent surgical treatment. The molecular and biologic factors underlying meningioma development are only now beginning to be understood. Genetic factors such as mutations in the neurofibromatosis-2 gene and in chromosomes 1, 9, and 10 play important roles in meningioma development and may be responsible for atypical tumors in some cases. Cellular factors such as telomerase activation and tyrosine kinase receptor mutations may also play an important role. Finally, autocrine and paracrine factors including epidermal growth factor receptor, platelet-derived growth factor-1, and fibroblast growth factor have been implicated in the development of some tumors. Although the relationship between the various factors implicated in tumor development is unknown, understanding these factors will be critical in the treatment of malignant or surgically inaccessible tumors.

Deletion at chromosome arm 9p in relation to BRAF/NRAS mutations and prognostic significance for primary melanoma

We report an investigation of gene dosage at 9p21.3 and mutations in BRAF and NRAS, as predictors of relapse and histological markers of poor melanoma prognosis. Formalin-fixed primary melanomas from 74 relapsed and 42 nonrelapsed patients were sequenced for common BRAF and NRAS mutations (N = 71 results) and gene dosage at 9p21.3 including the genes CDKN2A (which encodes CDKN2A and P14ARF), CDKN2B (CDKN2B), and MTAP was measured using multiplexed ligation-dependant probe amplification (MLPA), (N = 75 results). BRAF/NRAS mutations were detected in 77% of relapsers and 58% of nonrelapsers (Fisher's exact P = 0.17), and did not predict ulceration or mitotic rate. There was no relationship between BRAF/NRAS mutations and gene dosage at 9p21.3. Reduced gene dosage at MTAP showed a borderline association with BRAF mutation (P = 0.04) and reduced gene dosage at the interferon gene cluster was borderline associated with wild type NRAS (P = 0.05). Reduced gene dosage in the CDKN2A regions coding for CDKN2A was associated with an increased risk of relapse (P = 0.03). Reduced gene dosage across 9p21.3 was associated with increased tumor thickness, mitotic rate, and ulceration (P = 0.02, 0.02, and 0.002, respectively), specifically in coding regions impacting on CDKN2B and P14ARF and CDKN2A. Loss at MTAP (P = 0.05) and the interferon gene cluster (P = 0.03) on 9p21 was also associated with tumor ulceration. There was no association between reduced gene dosage at 9p21.3 and subtype or site of tumor. This study presents supportive evidence that CDKN2B, P14ARF, and CDKN2A may all play a tumor suppressor role in melanoma progression.

Similar nucleotide excision repair capacity in melanocytes and melanoma cells

Sunlight UV exposure produces DNA photoproducts in skin that are repaired solely by nucleotide excision repair in humans. A significant fraction of melanomas are thought to result from UV-induced DNA damage that escapes repair; however, little evidence is available about the functional capacity of normal human melanocytes, malignant melanoma cells, and metastatic melanoma cells to repair UV-induced photoproducts in DNA. In this study, we measured nucleotide excision repair in both normal melanocytes and a panel of melanoma cell lines. Our results show that in 11 of 12 melanoma cell lines tested, UV photoproduct repair occurred as efficiently as in primary melanocytes. Importantly, repair capacity was not affected by mutation in the N-RAS or B-RAF oncogenes, nor was a difference observed between a highly metastatic melanoma cell line (A375SM) or its parental line (A375P). Lastly, we found that although p53 status contributed to photoproduct removal efficiency, its role did not seem to be mediated by enhanced expression or activity of DNA binding protein DDB2. We concluded that melanoma cells retain capacity for nucleotide excision repair, the loss of which probably does not commonly contribute to melanoma progression.

Comparative genome hybridization analysis of laser-capture microdissected in situ melanoma

BACKGROUND

The progression of melanoma occurs through discrete stages with known clinical and histologic features. Although many molecular events that occur during the progression of invasive and metastatic melanomas have been elucidated, there is limited knowledge of genetic changes that occur in the earliest stages of melanoma development. In this pilot study, we investigated genetic changes that happen in in situ melanoma so that we can better understand early melanoma development.

MATERIALS AND METHODS

DNA was extracted from five laser-capture microdissected Clark's level III melanomas, five in situ melanomas and five compound nevi all from sun exposed skin. Array-based comparative genomic hybridization was performed using Agilent 44 K platform.

RESULTS

The group of Clark's level III melanomas was characterized with multiple large deletions and duplications. In the group of in situ melanoma, deletions and duplications were limited in size. Deletions in in situ melanomas were present only on chromosomes 13q and 16q. Compound nevi did not show any significant chromosomal aberrations.

CONCLUSION

In situ melanomas show characteristic chromosomal aberrations that are limited compared to melanomas that invade the dermis. Deletion of 13q found in in situ melanomas, which encompass the Rb1 tumor suppressor gene, might be one of the first events in the development of melanoma.

Allelotyping, microsatellite instability, and BRAF mutation analyses in common and atypical melanocytic nevi and primary cutaneous melanomas

Loss of heterozygosity (LOH) in several chromosomal regions is found in melanoma, and it has been partially studied in nevi. BRAF mutations are found in melanoma and nevi and in colorectal cancer are linked to mismatch repair deficiency. We studied early genetic events involved in melanomagenesis through analysis of allelic loss, microsatellite instability (MSI), and BRAF mutations. DNA extracted from microdissected cells of 22 common nevi, 23 atypical nevi, and 25 primary cutaneous melanomas were examined for LOH and MSI by polymerase chain reaction-based analysis of 24 microsatellite markers and BRAF mutation. Allelic loss index was higher in atypical nevi (0.20) and melanomas (0.27) than common nevi (0.07). LOH was frequent at 9p21, 17q21, 6q23, and 5q35 in melanoma. LOH at any of this loci occurred in 27% of common nevi, 57% of atypical nevi, and 68% of melanomas. BRAF mutations were not related to MSI presence and MSI index was not related with BRAF mutational status. Similar genetic alterations in atypical nevi and melanomas support the concept of atypical nevus as melanoma precursor. Novel deletion loci at 5q35 and 17q21 (BRCA1) in atypical nevi and melanomas were identified. Mismatch repair deficiency is not a crucial event for BRAF mutation in melanocytic tumors.

Characterization of 9p21 copy number alterations in human melanoma by fluorescence in situ hybridization

Alteration of the CDKN2A (alias p16) tumor suppressor gene, located on 9p21, occurs frequently in familial and sporadic melanomas. Beside CDKN2A, other genes (e.g., CDKN2B, and ARF/p14(ARF), long considered distinct from CDKN2A) on this locus are often deleted or mutated in a large number of tumors including glioma, bladder cancer, and lung cancer. The aim of this study was to evaluate the deletion pattern of the 9p21 locus on a cell-by-cell basis in a large number of melanoma samples using fluorescence in situ hybridization (FISH). In an analysis of 81 primary lesions targeting the 9p21 region and chromosome 9 centromere, high frequency of 9p21 loss (84%) was found. Deletion of 9p21 was present in both early- and late-stage melanomas with similar frequencies. Extra 9p21 copies were rarely seen; they were always associated with polysomy 9 and were observed only in advanced stage melanomas (6 tumors). This FISH study strengthens the hypothesis that the loss of 9p21 occurs frequently in primary melanoma, that the deletion is present in early and late stages of the disease with similar frequency, and that it affects a large extent of the locus.

Cutaneous melanoma: pathogenesis and rationale for chemoprevention

OBJECTIVE

To critically review aspects of melanoma pathogenesis that lend themselves to a chemoprevention strategy. To discuss potential candidate chemoprevention agents with an emphasis on the lipid lowering drugs, the statins, currently, the most promising agents.

DATA SOURCES

A retrospective review of the literature.

STUDY SELECTION

Studies included those relevant to melanoma pathogenesis, to the scientific rationale of chemoprevention, and pertinent epidemiologic, pre-clinical, and clinical studies. The referenced study designs and methodologies varied.

DATA EXTRACTION AND SYNTHESIS

Data were extracted by two reviewers, and the main results are presented in a quantitative descriptive manner.

CONCLUSION

Melanoma is a preventable disease by altering behavior (sun exposure) among at-risk individuals. There is also considerable evidence to suggest that melanoma development may be prevented or delayed by drugs of sufficiently low toxicity to make clinical trials of chemoprevention feasible and potentially successful. Among potential candidate agents, statins have compelling data for long-term safety and sufficient pre-clinical and clinical evidence for efficacy to justify their evaluation in well-designed trials in high-risk individuals, incorporating intermediate biologic endpoints.

p53 protein expression and TP53 mutations in malignant melanomas of sun-sheltered mucosal membranes versus chronically sun-exposed skin

In this paper, we compare the expression of the TP53 gene product, p53 protein (p53p), in primary malignant melanomas from sun-shielded mucous membranes and from chronically sun-exposed skin. Archival tissues from 29 patients with mucosal melanomas and from 27 with cutaneous melanomas in facial skin were subjected to immunohistochemical procedures using the monoclonal antibody DO-1. p53p expression did not differ significantly between the two groups of melanomas. A comparison with previously obtained data on TP53 mutations from the same tumours showed closer concordance amongst mucosal than amongst skin tumours. Primary mucosal melanomas and their satellites showed identical patterns, focal or diffuse, of p53p expression. Thus, expression of altered p53p could well participate in the clonal expansion of these mucosal melanomas and in tumour progression. The p53p characteristics recognized in our investigations are amongst the first hallmarks in the emerging molecular pathological profiling of mucosal melanomas, and may therefore be useful in exploring the aetiology of UV-independent melanomas.

Repetitive DNA alterations in human skin cancers

Repetitive sequences constitute landmarks for genome regulation, evolution, and chromatin architecture. Patterns of specific and non-specific repetitive sequences change in many types and stages of tumor cells, characterized by band loss, gain, and (de) increased staining of pre-existing bands. In this work, repetitive DNA was studied in search of genome instability of skin cancers: basal and squamous cell carcinomas (BCC and SCC), malignant melanoma (MM), melanocytic nevus (MN), and actinic keratosis (AK) lesions. DNAs were extracted from blood and tumor samples from 21 BCC, 7 SCC, 11 MM and 7 lesions. Banding patterns were obtained by random amplification of polymorphic DNA (RAPD), and specific D9S50 and D9S52 microsatellites (9p21). D9S50 patterns revealed microsatellite instability (MSI) and/or loss of heterozygosity (LOH) in 36% BCC, 25% SCC, and 57% MM tumors. D9S52 microsatellite showed 28.5%; 42.8%; and 71.4% altered tumors, respectively. No microsatellite alterations were found in MN and AK. On the other hand, genomic rearrangements detected by RAPD were present in 100% tumors. In BCC, the mean number of tumor DNA alterations showed predominant gain of bands. On the contrary, MM samples presented loss, or decreased intensity signal of RAPD bands. Genome alterations in skin cancers would result from chromosomal rearrangements, aneuploidy and/or polysomies. The low-cost and quick RAPD technique may reveal unknown genes or DNA sequences associated with tumor development and progression, and may be easily implemented in clinical diagnosis.

Variability in nomenclature used for nevi with architectural disorder and cytologic atypia (microscopically dysplastic nevi) by dermatologists and dermatopathologists

BACKGROUND

Although a nevus with the microscopic features of a "dysplastic nevus" is commonly seen, the nomenclature used to describe such a lesion has been thought to be inconsistent. A 1992 National Institutes of Health (NIH) Consensus Conference sought to unify nomenclature and suggested that the term "nevus with architectural disorder" be used along with a comment on melanocytic atypia.

METHODS

We performed a cross-sectional mail survey to determine preferred terminology as well as the level of adherence to the NIH-recommended nomenclature. All 856 active members of the American Society of Dermatopathology (ASDP) and 1100 (13.0%) of the 8471 active members of the American Academy of Dermatology (AAD) were surveyed.

RESULTS

Five hundred and thirty-three ASDP members and 483 AAD members who fulfilled eligibility criteria completed the questionnaire. The term "dysplastic nevus" was favored by the largest number of responders (favored by 39.1% of ASDP members and 62.3% of AAD members), while the 1992 NIH Consensus Conference-recommended terminology was the second most popular term (25.3% of ASDP and 15.1% of AAD members). Dermatopathologists (OR = 1.9, p = 0.0001) and those who had dual training in dermatology and dermatopathology (OR = 1.6, p = 0.02 for ASDP members; OR = 2.3, p = 0.02 for AAD members) were more likely to adhere to the 1992 NIH Consensus Conference nomenclature.

CONCLUSIONS

Despite attempts to unify nomenclature for microscopically dysplastic nevi through the NIH Consensus Conference, wide variation in terminology persists.

Pharmacogenetic candidate genes for melanoma

The incidence of melanoma is rising at an alarming rate and has become an important public health concern. If detected early, melanoma carries an excellent prognosis after appropriate surgical resection. Unfortunately, advanced melanoma has a poor prognosis and is notoriously resistant to radiation and chemotherapy. The relative resistance of melanoma to a wide-range of chemotherapeutic agents and high toxicity of current therapies has prompted a search for effective alternative treatments that would improve prognosis and limit side effects. Advances in molecular genetics are revealing in increasing detail the mechanisms responsible for the development of melanoma. Hopefully, elucidation of these pathways will provide a means of screening high-risk individuals and allow new drug development for prevention and treatment by identification of specific pharmacological targets. This review will summarize the genetics of melanoma with the goal of providing insights into potential pharmacogenetic candidate genes.