Detection of microsatellite alterations in the spectrum of melanocytic nevi in patients with or without individual or family history of melanoma

Microsatellite Instability: From the Implementation of the Detection to a Prognostic and Predictive Role in Cancers

Microsatellite instability (MSI) has been identified in several tumors arising from either germline or somatic aberration. The presence of MSI in cancer predicts the sensitivity to immune checkpoint inhibitors (ICIs), particularly PD1/PD-L1 inhibitors. To date, the predictive role of MSI is currently used in the selection of colorectal cancer patients for immunotherapy; moreover, the expansion of clinical trials into other cancer types may elucidate the predictive value of MSI for non-colorectal tumors. In clinical practice, several assays are used for MSI testing, including immunohistochemistry (IHC), polymerase chain reaction (PCR) and next-generation sequencing (NGS). In this review, we provide an overview of MSI in various cancer types, highlighting its potential predictive/prognostic role and the clinical trials performed. Finally, we focus on the comparison data between the different assays used to detect MSI in clinical practice.

Altered Expression of the Dna Mismatch Repair Proteins Hmlh1 and Hmsh2 in Cutaneous Dysplastic Nevi and Malignant Melanoma

Molecular alterations in the mismatch repair system suggest that this mechanism may be important in the evolution of cutaneous melanoma. Our current study evaluated the expression of two mismatch repair proteins, hMLH1 and hMSH2, in dysplastic nevi (DN) and cutaneous melanoma (CM). Immunohistochemical staining of these proteins was performed on 55 CM and 30 DN specimens. The staining results were divided into three groups: negative, partially positive and strongly positive. Normal adjacent skin cells served as an internal control for positive immunostaining. Altered immunoreactivity of one of the proteins was found in four (13.4%) DN and seven (12.7%) CM. Lack of staining for hMLH1 was observed in two (6.7%) cases of DN and five (9.1%) cases of CM; staining for hMSH2 was absent in two (6.7%) of the DN and two (3.6%) of the CM specimens. Partially positive staining was found in 33.3% and 53.3% for hMLH1 and hMSH2, respectively, in DN, and in 54.5% and 69.1%, respectively, in CMM. Our study shows that complete or partial loss of MMR protein expression occurs in a subset of both DN and CM and may represent a distinct pathway in the development of some DN and CM.

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.

Deficient mismatch repair: Read all about it (Review)

Defects in the DNA mismatch repair (MMR) proteins, result in a phenotype called microsatellite instability (MSI), occurring in up to 15% of sporadic colorectal cancers. Approximately one quarter of colon cancers with deficient MMR (dMMR) develop as a result of an inherited predisposition syndrome, Lynch syndrome (formerly known as HNPCC). It is essential to identify patients who potentially have Lynch syndrome, as not only they, but also family members, may require screening and monitoring. Diagnostic criteria have been developed, based primarily on Western populations, and several methodologies are available to identify dMMR tumours, including immunohistochemistry and microsatellite testing. These criteria have provided evidence supporting the introduction of reflex testing. Yet, it is becoming increasingly clear that tests have a limited sensitivity and specificity and may yet be superseded by next generation sequencing. In this review, the limitations of diagnostic criteria are discussed, and current and emerging screening technologies explained. There is now useful evidence supporting the prognostic and predictive value of dMMR status in colorectal tumours, but much less is known about their value in extracolonic tumours, that may also feature in Lynch syndrome. This review assesses current literature relating to dMMR in endometrial, ovarian, gastric and melanoma cancers, which it would seem, may benefit from large-scale clinical trials in order to further close the gap in knowledge between colorectal and extracolonic tumours.

Implication of the β2-microglobulin gene in the generation of tumor escape phenotypes

Classical MHC molecules present processed peptides from endogenous protein antigens on the cell surface, which allows CD8(+) cytotoxic T lymphocytes (CTLs) to recognize and respond to the abnormal antigen repertoire of hazardous cells, including tumor cells. The light chain, β2-microglobulin (β2m), is an essential constant component of all trimeric MHC class I molecules. There is convincing evidence that β2m deficiency generates immune escape phenotypes in different tumor entities, with an exceptionally high frequency in colorectal carcinoma (CRC) and melanoma. Damage of a single β2m gene by LOH on chromosome 15 may be sufficient to generate a tumor cell precommitted to escape. In addition, this genetic lesion is followed in some tumors by a mutation of the second gene (point mutation or insertion/deletion), which produces a tumor cell unable to express any HLA class I molecule. The pattern of mutations found in microsatellite unstable colorectal carcinoma (MSI-H CRC) and melanoma showed a striking similarity, namely the predominance of frameshift mutations in repetitive CT elements. This review emphasizes common but also distinct molecular mechanisms of β2m loss in both tumor types. It also summarizes recent studies that point to an acquired β2m deficiency in response to cancer immunotherapy, a barrier to successful vaccination or adoptive cellular therapy.

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.

Dysplastic nevi

Dysplastic nevi have been a subject of much debate since their original description in 1978. Although some question the biological potential of dysplastic nevi themselves, several studies have shown that their presence confers substantial risk for melanoma. In addition to predisposing patients to melanoma, dysplastic nevi have been shown to harbor genetic mutations, indicating their position on a continuum between banal nevi and melanomas. Dysplastic nevi are also clinically relevant as mimickers of melanoma, and can be challenging diagnostically. This article reviews the history, epidemiology, biology and genetics, clinical features, histopathologic features, and management guidelines for patients with these lesions.

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.

DNA mismatch repair protein expression and microsatellite instability in primary mucosal melanomas of the head and neck

AIMS

To examine the expression of DNA mismatch repair (MMR) proteins and the presence of microsatellite instability (MSI) in seven primary mucosal melanomas of the head and neck (MMHN).

METHODS AND RESULTS

Haematoxylin and eosin staining and immunohistochemical analysis for routine diagnostic markers and for MMR proteins were performed. Six cases were examined for MSI. Four cases were monomorphous and three cases were pleomorphic type MMHN. Melanocytic markers were positive in all cases. Immunoreactivity for MMR proteins was weak in normal epithelium. The neoplastic tissue in six cases showed positivity for all MMR proteins with different percentages. One case showed weak positivity for hMSH2 and hMSH6 and no immunoreactivity for hMLH1 or hPMS2. Staining intensity was higher in tumour cells than in matched normal mucosa in three cases for hMSH2 and hMLH1 and in two cases for hPMS2. None of the examined cases showed MSI.

CONCLUSIONS

Expression of hMSH2 and hMLH1 proteins was up-regulated in three cases, whereas in two cases that of hPMS2 was increased. hMSH6 expression was comparable to that of normal cells in all cases. The percentage of positive neoplastic cells and the intensity of staining seemed to be greater in pleomorphic melanomas. Six cases were MMR-proficient and microsatellite stable.

Genomic stability in malignant melanoma of Xiphophorus

Microsatellite instability is a feature of many tumours and is indicative of a generalized genomic instability of cancer cells. Whether this phenomenon is essential for tumorigenesis and whether it is an early or late step is still a matter of debate. In the Xiphophorus melanoma model, the primary steps leading to tumour formation are known and include overexpression of a mutationally altered epidermal growth factor receptor and the resulting defects in signalling. We have analysed the late stages of melanoma progression for microsatellite instability. Although several types of microsatellite allele alteration in DNA from tumours relative to DNA from non-tumour tissue were found, the frequency was rather low (7.6%). Thus, although the tumours show a wide range of malignancy and aggressiveness, genomic instability that becomes apparent as microsatellite instability does not appear to be an obligatory step for melanoma progression.

De novo intraepidermal epithelioid melanocytic dysplasia as a marker of the atypical mole phenotype - a clinical and pathological study of 75 patients

BACKGROUND

We encountered a distinctive pattern of dysplastic intraepidermal melanocytic proliferation, which defies classification as a dysplastic melanocytic nevus, but in which the morphologic features fall short of a diagnosis of melanoma in situ. We designate such lesions as de novo intraepidermal epithelioid melanocytic dysplasia.

METHODS

From 75 patients, 82 skin biopsies were encountered that showed this distinctive morphology. Hematoxylin- and eosin-stained histologic sections were studied and the features were correlated with personal and family histories of dysplastic nevi and melanoma.

RESULTS

The diagnosis of de novo melanocytic dysplasia was made in 27 male patients and 48 female patients (mean age: 44 years). The histologic hallmark was a pagetoid (single-cell) array of moderately to severely atypical epithelioid melanocytes within the epidermis. Seventy-three lesions were located on sun-exposed skin and nine on sun-protected skin. In 41 patients, there was an atypical mole phenotype, whereas 20 patients had a prior or subsequent diagnosis of melanoma with five of 16 patients questioned revealing a family history of melanoma.

CONCLUSIONS

De novo intraepidermal epithelioid melanocytic dysplasia is a distinct entity associated with an atypical mole phenotype and a personal and/or family history of melanoma.

Comparative Analysis of Loss of Heterozygosity and Microsatellite Instability in Adult and Pediatric Melanoma

Although 0.3% of melanomas occur in children, the incidence has risen in past decades. In adult melanoma, some chromosomal regions in 1p, 6q, 9p, 10q, and 11q are frequently deleted. Microsatellite instability (MSI), which reflects impaired DNA repair, has been found at low levels in adult melanoma and melanocytic nevi. To investigate the molecular changes in pediatric melanoma, a screening for loss of heterozygosity and microsatellite instability was performed and compared with changes found in adult melanoma. Formalin-fixed, paraffin-embedded tissues from 10 adult melanomas, 9 melanocytic nevi, and 8 pediatric melanomas were microdissected and the DNA was extracted. Loss of heterozygosity and microsatellite instability were evaluated using 13 microsatellite repeat polymorphisms located in 1p36, 1q32, 2p12, 2p22-25, 2q33-37, 9p21, 10q23.3, 11q23, 13q14, 17p13, and 17q21. The overall frequency of loss of heterozygosity was 0.09 for nevi, 0.30 for adult melanoma, and 0.43 for pediatric melanoma (nevi vs. adult melanoma, P = 0.0082; nevi vs. pediatric melanoma, P = 0.0092). Pediatric melanoma has more loss of heterozygosity (44%) in 11q23 than adult melanoma (7%, P = 0.046). The microsatellite instability overall frequency was greater in pediatric melanoma (0.24) than nevi (0.05, P = 0.0031) and adult melanoma (0.09, P = 0.0195). Our findings suggest that pediatric melanoma has a different abnormal pattern than adult melanoma. Pediatric melanoma has more microsatellite instability than adult melanoma. 11q23 could contain genes related to the early age onset of melanoma. The high frequency of microsatellite instability is coincidental with the finding of higher levels of microsatellite instability in pediatric brain tumors and could play a role in the pathogenesis of pediatric melanoma.

Melanocytic dysplastic naevi occupy the middle ground between benign melanocytic naevi and cutaneous malignant melanomas: emerging clues

Although several studies have confirmed the aetiological importance of melanocytic dysplastic naevi (MDN) in the development of cutaneous malignant melanoma (CMM), the analysis of these lesions was directed mostly towards the study of melanomas. The underlying reasons include the relatively large size of CMMs, their direct lethal outcome, and the feasibility of establishing melanoma cell lines. In contrast, because of their relatively small size, questionable malignant potential, and the difficulty in establishing in vitro cultures, MDN have been studied less extensively. Hypothetically, transformed melanocytes can give rise to any lesion in the hierarchy of melanocytic tumours. Based on this hypothetical perspective, and on the epidemiological, morphological, immunohistochemical, and genetic characteristics of MDN, it is not surprising that these lesions occupy an intermediate position in the hierarchy of melanocytic lesions, and may be precursors of CMM. Although this argument appears to be straightforward, it is still controversial. This review explores the components of this argument and provides supporting evidence for this hypothesis.

Genetic progression of metastatic melanoma

Melanoma progression is well defined in its clinical, histopathological and biological aspects, but the molecular mechanism involved and the genetic markers associated to metastatic dissemination are only beginning to be defined. The recent development of high-throughput technologies aimed at global molecular profiling of cancer is switching on the spotlight at previously unknown candidate genes involved in melanoma, such as WNT5A and BRAF. In fact, several tumor suppressors and oncogenes have been shown to be involved in melanoma pathogenesis, including CDKN2A, PTEN, TP53, RAS and MYC, though they have not been related to melanoma subtypes or validated as prognostic markers. Here, we have reviewed the published data relative to the major genes involved in melanoma pathogenesis, which may represent important markers for the identification of genetic profiles of melanoma subtypes.

Genetic pathways to melanoma tumorigenesis

The incidence of cutaneous malignant melanomas is growing faster than that of any other cancer and therefore posing a major heath threat worldwide. In melanocytic skin tumours, the feasibility of correlating a specific pathological stage with a corresponding genetic alteration provides a remarkable opportunity to study the multistep tumorigenesis model. This multistep melanoma tumorigenesis is best described as a continuum of transformation of the melanocytes, melanocytic dysplasia, and melanoma formation. These steps involve genotypic alterations including loss of tumour suppressor genes, microsatellite instability, and alterations of the mismatch repair system. This review seeks to examine melanoma tumorigenesis based on these genetic changes.

Instability of microsatellites is an infrequent event in uveal melanoma

Microsatellite instability (MSI) is a distinct tumour phenotype that is associated with alterations of DNA mismatch repair and is being increasingly reported in a number of hereditary and sporadic tumours. Numerous reports have suggested that melanocytic neoplasms, including cutaneous melanomas, frequently demonstrate low frequency MSI, whilst a small number of tumours exhibit high frequency MSI. Furthermore, loss of expression of DNA mismatch repair proteins has been associated with progression from benign to malignant disease in melanocytic neoplasms, but the presence or absence of mismatch repair defects in uveal melanomas has yet to be determined. This study was designed to establish whether MSI is a feature of these ocular melanomas. To investigate the prevalence of MSI in uveal melanomas, 52 tumours were analysed by polymerase chain reaction amplification of a panel of microsatellite markers selected for their ability to detect tumours exhibiting defects in DNA mismatch repair mechanisms. MSI was rarely detected in the 52 uveal melanomas analysed. All tumours demonstrated stable microsatellites at five of the six microsatellite markers tested (BAT26, BAT40, APC, D2S123 and Mfd15CA). Only one tumour showed the presence of a single unstable allele at a tetranucleotide marker (MYCL1). These data suggest that high frequency MSI does not occur in these tumours, and that low frequency MSI, in contrast to cutaneous melanoma, is a rare event in malignant melanomas of the uveal tract.

What is new in melanoma research: genetics and epidemiology of melanoma in 2003? Review of a workshop held in Milan in May 2003

The various papers that were presented during this symposium touched on two of the most important aspects concerning melanoma because they dealt with epidemiology and genetics. Secondary prevention represents the most important step to cure melanoma patients once the disease has presented on a patient. It is clear that educational campaigns lead to greater awareness of the public and hence better prevention and earlier diagnosis. A second item is becoming more and more important in the field of prevention and early diagnosis, which is to understand the genetic basis of melanoma etiology and development. Studies concerning the familial clustering, for example, can lead to more careful monitoring of patients for other tumours and also lead to a basis for further research.

Expression and localization of mutant p16 proteins in melanocytic lesions from familial melanoma patients

Little is known about the correlation between the loss of p16 expression and tumor progression in familial melanoma; no systematic study has been conducted on p16 expression in melanocytic tumors from patients carrying germline CDKN2A mutations. We analyzed 98 early primary lesions from familial patients, previously tested for germline CDKN2A status, by quantitative immunohistochemistry using 3 p16 antibodies. We found that p16 expression was inversely correlated with tumor progression and was significantly lower in melanomas, including in situ lesions, than in nevi. Of other features analyzed, tumor thickness showed the most significant correlation with p16 levels. Lesions from mutation-negative patients displayed combined nuclear and cytoplasmic staining. However, some mutation-positive lesions (ie, G101W, 113insR, M53I, R24P, and 33ins24), including benign nevi, showed nuclear mislocalization, confirming previous studies suggesting that subcellular distribution indicates functional impairment of p16.

Mutation analysis of candidate genes in melanoma-prone families

Putative tumour suppressor genes CDKN2A and CDKN2B (on chromosome 9p21) and CDKN2A-interacting cell growth regulatory genes CDK4 and Id-1 have been demonstrated to be involved in the pathogenesis of malignant melanoma (MM). Mutation analysis of these candidate genes was performed in MM families from southern Italy with three or more affected members or two affected members and one or more relative with histologically diagnosed atypical naevus. Two CDKN2A mutations, Arg24Pro and 1-292 G>A, were observed in two (15%) families; except for CDKN2A and Id-1 polymorphisms, no sequence variations were detected in the remaining genes. Screening among 119 sporadic MM cases revealed two additional CDKN2A mutations at very low prevalences. Identification of a large shared haplotype at 9p21 in some MM families negative for CDKN germline mutations suggests that other CDKN-inactivating mechanisms may be responsible for MM predisposition or, alternatively, additional susceptibility gene(s) may be present on chromosome 9p21. Fluorescence in situ hybridization analysis of a subset of MM tissue sections seemed to indicate that the D9S171 locus may be involved in MM pathogenesis.

[The dysplastic nevus. Separate entity, melanoma precursor or diagnostic dilemma?]

Today, 20 years after Clark and Elder postulated their tumor progression model of melanocytic lesions from common nevi to melanoma, there are still controversies surrounding this subject. Despite modem molecular biological developments, a consensus about the question, if the dysplastic nevus should be considered as a separate entity, melanoma precursor or just represent a diagnostic dilemma, still seems to be impossible. In addition, since the term melanocytic dysplasia is not precisely defined with regard to all diagnostic methods (clinical morphology, dermatoscopy, dermatopathology, molecular biology), there is considerable confusion. The question remains if a quite arbitrary classification of melanocytic lesions such as dysplastic nevus is useful at all. In daily practice, dermatologists should be aware of the fact that each suspicious melanocytic lesion could represent an early malignant neoplasia, regardless whether it is formally named dysplastic nevus or initial malignant melanoma. We conclude that solid dermatological experience plus novel tools of documentation represent the key factor to minimize patients' risk.

TP53, p14ARF, p16INK4a and H-ras gene molecular analysis in intestinal-type adenocarcinoma of the nasal cavity and paranasal sinuses

Intestinal-type adenocarcinoma (ITAC) of the nasal cavity and paranasal sinuses is an uncommon tumor associated with occupational exposure to dusts of different origin. Few investigations addressed molecular alterations in ITAC mainly focused on TP53, K-ras and H-ras gene mutations. The occurrence of TP53, p14(ARF) and p16(INK4a) deregulation and H-ras mutations was investigated in 21 consecutive and untreated ITACs cases, 17 with known professional exposure. No H-ras mutations were found. In patients with known exposure, cumulative evidence of TP53 or p14(ARF) alterations accounted for 88% and the evidence of p16(INK4a) alterations for 65%, respectively. TP53 mutations were present in 44% of the ITACs, consisted of G:C-->A:T transitions in 86%, and involved the CpG dinucleotides in 50% of the cases. LOH at the locus 17p13 and an uncommon high rate of p53 stabilization were detected in 58% and 59% of the cases, respectively. p14(ARF)and p16(INK4a) promoter methylation accounted for 80% and 67% respectively, and LOH at the locus 9p21 occurred in 45% of the cases. Interestingly, all dust-exposed tumors with p16(INK4a) alterations shared TP53 or p14(ARF) deregulation. The present results show a close association of this occupational tumor with TP53, p14(ARF) and p16(INK4a) gene deregulation. Given the important role that these genes play in cell growth control and apoptosis, the knowledge of ITAC genetic profile may be helpful in selecting more tailored treatments.

Assessment of genetic instability in melanocytic skin lesions through microsatellite analysis of benign naevi, dysplastic naevi, and primary melanomas and their metastases

Microsatellite instability (MSI) is caused by replication errors due to deficient DNA mismatch repair and has been associated with tumour progression in various types of cancer. Controversial results have been reported concerning the frequency and significance of MSI in malignant melanoma. In this study, the time of onset and relative incidence of MSI were determined during the progression of melanocytic tumours, starting with benign melanocytic naevi. MSI was studied at 13 loci containing single, di- or trinucleotide repeat sequences and mapping to five different chromosomal locations. Tumours were classified as being low frequency MSI (L-MSI+) or high frequency MSI (H-MSI+) when either one or at least two marker loci, respectively, displayed mutant alleles in tumour DNA compared with the corresponding normal tissue DNA. None of the eight melanocytic naevi studied showed MSI, whereas a moderate frequency of H-MSI was detected in dysplastic naevi (one out of 11; 9%) and primary melanomas (six out of 56; 11%). The incidence of H-MSI was increased in melanoma metastases from the same patients (nine out of 42; 21%). In contrast to previously reported data showing higher rates of MSI in melanoma, genetic instability seems to be present in a minority of malignant melanoma lesions. However, our findings are consistent with the hypothesis that MSI may be sequentially induced during malignant evolution, contributing to the progression of a subset of melanocytic tumours.

The clinical importance and prognostic implications of microsatellite instability in sporadic cancer

AIMS

The genetic abnormality known as microsatellite instability (MSI), first identified in colorectal cancer in 1993, has subsequently been recognised in other malignancies. These cancers are caused by a defect in the nuclear mismatch repair system, allowing mutations to accumulate with every cellular division. Hereditary Non Polyposis Colon Cancers (HNPCC) and associated malignancies demonstrating MSI have a unique histological appearance, improved prognosis and altered response to chemotherapy and radiotherapy. This review examines the incidence of MSI and its clinical significance in commonly occurring solid malignancies.

METHOD

A medline based literature search was performed using the key words 'Microsatellite Instability' and the name of the specific malignancy being investigated. Additional original papers were obtained from citations in those articles identified in the original medline search.

RESULTS

MSI has been detected in many solid malignancies although the definition of instability applied has been variable. It is most commonly found in sporadic malignancies that also occur in the HNPCC syndrome such as colorectal, stomach, endometrial and ovarian cancer. MSI may impart a favorable prognosis in colorectal, gastric, pancreatic and probably oesophageal cancers but a poor prognosis in non small cell lung cancer. In clinical studies colorectal cancers demonstrating MSI respond better to chemotherapy while in vitro studies using MSI positive cell lines show resistance to radiotherapy and chemotherapy.

CONCLUSION

MSI may be a useful genetic marker in prognosis and could be an influential factor in deciding treatment options. However, in many cancers its significance remains unclear and more evaluation is required.

Genotypic analysis of primary and metastatic cutaneous melanoma

Microdissection genotyping was performed on 16 cases of melanoma, including two cutaneous and one lymph node metastases. Three benign nevi were used as controls. Where possible, tumor was microdissected at several sites. Genotyping involved assessment of loss of heterozygosity [LOH]), which was accomplished using a panel of nine polymorphic tetranucleotide microsatellites. Polymerase chain reaction was performed on the normal tissue sample to establish microsatellite heterozygous status. Informative markers were then tested on microdissected lesional tissue and scored for the presence and extent of allelic imbalance (AI). Microsatellite informativeness varied from 33% to 66%. Benign nevi were without AI. All invasive melanomas manifested acquired allelic loss, which involved 75% or 100% of the markers shown to be informative for each subject. Eleven of 13 (84%) primary melanomas demonstrated intratumoral heterogeneity of AI consistent with development of tumor subclones with differing genotypic profiles within thin as well as thick melanomas. Although a consistent pattern did not emerge among the markers, LOH of 9p21 (D9S254) occurred in 60% (9/15) of the cases followed by 40% of cases displaying LOH of 1p34, p53, 10q (MXI1), and 10q23 (D10S520) and 25% with 5q21 (D5S 592) abnormalities. A third of the cases including the metastatic foci demonstrated two different patterns of AI affecting alternative alleles of the same genomic marker within different parts of the melanoma. Two melanomas in situ did not display LOH of any markers in the informative cases although the in situ component in the invasive tumors had allelic losses that were in part similar to the invasive areas. The results of this study support the expanded use of microdissection genotyping and explore other markers to define the unique mutational profile for malignant melanoma that may complement other histologic characteristics of melanoma.

Loss of heterozygosity and microsatellite instability in acquired melanocytic nevi: towards a molecular definition of the dysplastic nevus

Acquired melanocytic nevi may show signs of histological dysplasia, and epidemiological studies have demonstrated that dysplastic melanocytic nevi (DMN) are associated with an elevated melanoma risk. Nevertheless, the concept of DMN as precursors of melanoma has remained a concept, in view of the difficulty of establishing unambiguous cytological and histological criteria for DMN. Recent molecular data suggest that genetic instability is more frequent in DMN than in benign acquired melanocytic nevi. We have analyzed 54 benign melanocytic nevi and 6 DMN for loss of heterozygosity (LOH) at microsatellite markers D9S171, IFNA, D9S270, D9S265. LOH at one or more loci was detected in 17 out of 54 benign nevi and in 4 out of 6 DMN. LOH was demonstrated at 26 out of 103 amplified and informative microsatellites in benign nevi and at 6 out of 11 microsatellites in DMN. In addition, 6 benign nevi and 6 DMN were microdissected in 4-15 regions per lesion and analyzed for LOH and microsatellite instability (MSI) at D9S162 and D14S53. Both LOH and MSI were detected more frequently in dysplastic nevi (LOH frequency 0.61 vs 0.18; MSI frequency 0.27 vs 0.05). These results confirm that genetic instability is more prevalent in DMN than in benign acquired melanocytic nevi. Therefore, DMN might be defined as a monoclonal and genetically unstable, but limited, melanocytic proliferation that distinguishes this entity from the benign nevus and from malignant melanoma.

The precursors of malignant melanoma

The precursors to melanoma are generally considered to be related to nevi of different types. Here we emphasize the dysplastic nevus, the congenital nevus, and lentigo maligna as specific lesions. The dysplastic nevus is discussed not only as a formal precursor but also as a marker of cutaneous melanoma. The clinical and histologic characteristics are outlined, as well as evidence of progression in dysplastic nevi. The congenital nevus is briefly reviewed and emphasis is placed upon clues to malignant degeneration. The concept of lentigo maligna as a precursor as distinct from an in situ phase is detailed.

Microsatellite analysis in cutaneous malignant melanoma

The status and relevance of repetitive nucleotide sequences or microsatellite alterations in sporadic cutaneous melanoma has not been fully clarified. In this study we evaluated the presence of microsatellite alterations in a series of sporadic primary and metastatic melanomas in order to discover which genetic events may have a pathogenetic role in the development of this disease. Tumour samples were obtained from 21 patients with sporadic cutaneous melanoma, and from eight corresponding positive sentinel lymph nodes and one corresponding in-transit metastasis. In each specimen, selected neoplastic cells were procured by laser-assisted microdissection. Polymerase chain reaction-based microsatellite analysis was performed using a panel of 11 microsatellite markers, located at chromosome 2p, 4q, 9p, 16q, 17p and 21q. Overall, we found microsatellite alterations in five (23.8%) melanomas. Of these, one case showed alteration at marker D2S2182 and one at marker D17S261, whereas in another case alterations at three loci, D2S2182, D2S2291 and D9S171, were found. The fourth patient demonstrated an alteration at locus D9S171 both in the primary tumour and in the histologically positive sentinel lymph node. The fifth case was characterized by alterations at D2S2182 and at D17S250, whereas the corresponding in-transit metastasis showed the same alterations as the primary tumour and an additional alteration at IFN alpha. In conclusion, our study confirms previous observations that cutaneous melanomas demonstrate microsatellite alterations, although such instability occurs at a lower frequency than specific mismatch repair defects. Genetic analysis of metastatic lesions revealed that the same microsatellite alterations as in the primary tumour are seen, but additional genetic changes may develop during disease progression.

Microsatellite instability and its relevance to cutaneous tumorigenesis

Increasing evidence suggests that human tumors sequentially accumulate multiple mutations that cannot be explained by the low rates of spontaneous mutations in normal cells (2-3 mutations/cell). The mathematical models estimate that for the solid tumors to develop, as many as 6-12 mutations are required in each tumor cell. Therefore, to account for such high mutation rates, it is proposed that tumor cells are genetically unstable, i.e. they have genome-wide mutations at short repetitive DNA sequences called microsatellites. Microsatellite repeats are scattered throughout the human genome, primarily in the non-coding regions, and can give rise to variants with increased or reduced lengths, i.e. microsatellite instability (MSI). This instability has been reported in an increasing number of cutaneous tumors including: melanocytic tumors, basal cell carcinomas and primary cutaneous T-cell lymphomas. Moreover, MSI has been observed in skin tumors arising in the context of some hereditary disorders such as Muir-Torre syndrome, Von Recklinghausen's disease and disseminated superficial porokeratosis. While MSI in some of these disorders reflects underlying DNA replication errors, the mechanism of instability in others is still unknown. Thus far, MSI is considered to be a distinct tumorigenic pathway that reveals surprising versatility. The ramifications for cutaneous neoplasms warrant further investigation.

Molecular aspects of melanocytic dysplastic nevi

Melanocytic dysplastic nevi were first described in both patients and their relatives who had one or several cutaneous malignant melanomas. Most of these dysplastic lesions are biologically stable, but some of them have severe histological atypia and can progress further to melanomas. Although several studies have suggested the etiological importance of dysplastic nevi in the development of melanomas, comprehensive reviews of the molecular changes in these dysplastic lesions are still scarce. To remedy this issue, this article analyzes the available molecular information about dysplastic nevi and provides the current state of knowledge regarding the karyotypic abnormalities of the melanoma/dysplastic nevus trait and the involvement of allelic loss, tumor suppressor genes, mismatch repair proteins, microsatellite instability, oncogenes, extracellular matrix proteins, and growth factors in the genesis of these lesions. These studies suggest that although some of these lesions represent "genetic dead-ends," others represent intermediate lesional steps in the melanoma tumorigenesis pathway.

Loss of heterozygosity analysis of cutaneous melanoma and benign melanocytic nevi: laser capture microdissection demonstrates clonal genetic changes in acquired nevocellular nevi

The molecular pathology of the common nevocellular nevus (NCN) and its relationship to the genetic model of malignant melanoma (MM) progression has not been fully characterized. We used laser capture microdissection of archival formalin-fixed material to study 34 melanocytic lesions (19 MM and 15 NCN). Twelve of the 15 NCN were acquired, 3 of which were congenital; none had dysplastic features. Ten polymorphic markers on five chromosomal regions (1p36, 6q22-23.3, 8p22-24, 10q23, and 11q23) were selected for loss of heterozygosity (LOH) analysis, based on previous studies demonstrating involvement in MM pathogenesis and progression. Loss of heterozygosity at any allelic locus was observed in 18 of 19 (95%) MM and in 9 of 15 (60%) NCN. Of the three congenital nevi analyzed, none showed LOH at any informative locus. The frequency of allelic loss was highest in the MM at 6q22-23.3 (64%), followed by 10q23 (62%), 8p22-24 (43%), 11q23 (43%), and 1p36 (13%). In the 15 NCN, the most frequent allelic losses were detected at 6q22-23.3 (29%), 1p36 (27%), and 10q23 (25%), with lower frequencies of LOH at 11q23 (10%) and 8p22-24 (7%). LOH at a single polymorphic marker, D6S1038, was detected in 70% of the MM and in 36% of the NCN, suggesting the presence of putative tumor-suppressor genes (TSGs) critical in melanocytic neoplasia at 6q22-23.3. The presence of clonal genetic alterations in acquired NCN justifies their classification as a benign neoplasm. The pattern of LOH in NCN is not random; rather, the relative frequencies of LOH at the chromosomal regions examined are consistent with a multistep model of MM progression that begins with NCN. Molecular analysis of NCN reiterates established epidemiologic and morphologic notions that NCN are precursor lesions for MM.

High-frequency microsatellite instability is associated with defective DNA mismatch repair in human melanoma

Hereditary nonpolyposis colorectal cancers and a steadily increasing number of sporadic tumors display microsatellite instability. In colorectal tumors, high-frequency microsatellite instability is strictly associated with inactivation of the DNA mismatch repair genes hMSH2, hMLH1, or hPMS2, whereas mutations in the mismatch repair gene hMSH6 have been identified in a subset of tumors with low-frequency microsatellite instability. In addition to epithelial tumors of the colon, endometrium, and ovary, microsatellite instability has been reported to occur also in sporadic melanoma. The relationship between microsatellite instability and mismatch repair in melanoma cells, however, has not been investigated so far. In this study, we analyzed microsatellite instability, mismatch repair activity, and expression of the hMSH2, hMSH6, hMLH1, and hPMS2 proteins in five melanoma cell lines and in tumor specimens from which the cells were derived. Four cell lines displayed normal levels of mismatch repair activity and expressed all the mismatch repair proteins. The extracts of the fifth cell line lacked the hMLH1 and hPMS2 proteins, and were correspondingly deficient in the repair of DNA mismatches. This line displayed high-frequency microsatellite instability, whereas the four mismatch-repair-proficient cell lines displayed either no or low-frequency microsatellite instability. These findings could be confirmed in the tumor specimens, in that only the tumor that did not express hMLH1 and hPMS2 displayed high-frequency microsatellite instability. Our data are consistent with the hypothesis that in melanoma, similarly to epithelial tumors, only the high-frequency microsatellite instability phenotype is strictly dependent on a defective mismatch repair system. Further studies on a large series of tumor specimens are required to establish the frequency of mismatch repair loss in human melanoma.

Comprehensive analysis of 112 melanocytic skin lesions demonstrates microsatellite instability in melanomas and dysplastic nevi, but not in benign nevi

INTRODUCTION

the length of DNA repetitive sequences (microsatellite instability (MSI)) represent distinct tumorigenic pathways associated with several familial and sporadic tumors.

MATERIAL AND METHODS

To investigate the prevalence and frequency of MSI in melanocytic lesions, the polymerase chain reaction (PCR)-based microsatellite assay was used to examine formalin-fixed, paraffin-embedded tissues of 30 benign melanocytic nevi, 60 melanocytic dysplastic nevi (MDN), and 22 primary vertical growth phase cutaneous malignant melanomas (CMM). Twenty-four microsatellite markers at the 1p, 2p, 3p, 4q and 9p chromosomal regions were used.

RESULTS

MSI was found at 1p and 9p in MDN and CMM but not in benign melanocytic nevi. The overall prevalence of MSI was 17/60 (28%) in MDN and 7/22 (31%) in CMM. The frequency of MSI ranged from 2/24 (9%) to 4/24 (17%) and was most commonly found at D9S162. There was a statistically significant correlation between degree of atypia and frequency of MSI (p<0.001) in MDN. There were two MSI banding patterns: band shifts and additional bands.

CONCLUSIONS

The data presented revealed the presence of low-frequency MSI (MSI-L) at the 1p and 9p regions in both MDN and CMM. Whether the MSI-L pattern reflects a defect in mismatch repair genes is still to be determined.

Alterations of mismatch repair protein expression in benign melanocytic nevi, melanocytic dysplastic nevi, and cutaneous malignant melanomas

Immunoperoxidase-staining methods were used to examine the expression of hMLH1, hMSH2, and hMSH6 mismatch repair (MMR) proteins in 50 melanocytic lesions. Microsatellite instability (MSI), screened previously in these lesions by polymerase chain reaction-based microsatellite assay, showed low-level microsatellite instability (MSI-L) in 11 of 22 melanocytic dysplastic nevi (MDN) and two of nine primary cutaneous malignant melanomas (CMMs) but not in the benign melanocytic nevi (BN). Mismatch repair proteins were widely expressed in the epidermis and adnexal structures. All lesions showed positive immunoreactivity with a gradual decrease in the MMR staining values during the progression from BN to MDN to CMMs. The average percentage of positively (PP) stained cells for hMLH1, hMSH2, and hMSH6 in BN was 85.50 +/- 1.95, 77.90 +/- 4.50, and 87.11 +/- 1.85, respectively. The PP cell values in CMMs were significantly reduced as compared with BN (75.22 +/- 3.57, p= 0.01; 56.11 +/- 8.73, p= 0.02; 65.22 +/- 6.47, p = 0.0002 for hMLH1, hMSH2, and hMSH6, respectively). No comparable significant difference was found between microsatellite stable and MSI-L lesions (p = 0.173, p = 0.458, and p = 0.385), suggesting a lack of correlation between MMR expression and MMR function. There was a direct correlation between PP cell values of hMSH2 and hMSH6 (R = 0.39, p = 0.008), implying that their expression could be regulated by a common mechanism. Thus, an important finding of these studies was the reduction of MMR protein levels in CMMs; whether this reflects underlying genetic or epigenetic mechanisms is still to be determined.

Rb and TP53 pathway alterations in sporadic and NF1-related malignant peripheral nerve sheath tumors

SUMMARY

Karyotypic complexities associated with frequent loss or rearrangement of a number of chromosome arms, deletions, and mutations affecting the TP53 region, and molecular alterations of the INK4A gene have been reported in sporadic and/or neurofibromatosis type I (NF1)-related malignant peripheral nerve sheath tumors (MPNSTs). However, no investigations addressing possible different pathogenetic pathways in sporadic and NF1-associated MPNSTs have been reported. This lack is unexpected because, despite similar morphologic and immunophenotypic features, NF1-related cases are, by definition, associated with NF1 gene defects. Thus, we investigated the occurrence of TP53 and p16(INK4A) gene deregulation and the presence of microsatellite alterations at markers located at 17p, 17q, 9p21, 22q, 11q, 1p, or 2q loci in MPNSTs and neurofibromas either related (14 cases) or unrelated (14 cases) to NF1. Our results indicate that, in MPNSTs, p16(INK4A) inactivation almost equally affects both groups. However, TP53 mutations and loss of heterozygosity involving the TP53 locus (43% versus 9%), and p53 wild type overexpression, related or not to mdm2 overexpression (71% versus 25%), seem to mainly be restricted to sporadic MPNSTs. In NF1-associated MPNSTs, our microsatellite results are consistent with the occurrence of somatic inactivation by loss of heterozygosity of the second NF1 allele.

Definition of the role of chromosome 9p21 in sporadic melanoma through genetic analysis of primary tumours and their metastases. The Melanoma Cooperative Group

Malignant melanoma (MM) is thought to arise by sequential accumulation of genetic alterations in normal melanocytes. Previous cytogenetic and molecular studies indicated the 9p21 as the chromosomal region involved in MM pathogenesis. In addition to the CDKN genes (p16/CDKN2A, p15/CDKN2B and p19(ARF), frequently inactivated in familial MM), widely reported data suggested the presence within this region of other melanoma susceptibility gene(s). To clearly assess the role of the 9p21 region in sporadic melanoma, we evaluated the presence of microsatellite instability (MSI) and loss of heterozygosity (LOH) in primary tumours as well as in synchronous or asynchronous metastases obtained from the same MM patients, using 9 polymorphic markers from a 17-cM region at 9p21. LOH and MSI were found in 27 (41%) and 11 (17%), respectively, out of 66 primary tumours analysed. In corresponding 58 metastases, MSI was found at higher rate (22; 38%), whereas a quite identical pattern of allelic deletions with 27 (47%) LOH+ cases were observed. Although the CDKN locus was mostly affected by LOH, an additional region of common allelic deletion corresponding to marker D9S171 was also identified. No significant statistical correlation between any 9p21 genetic alteration (LOH, MSI or both) and clinicopathological parameters was observed.