Dysplastic nevi can be diagnosed and graded reproducibly: a longitudinal study

Dysplastic naevi: an update

Dysplastic naevi are clinically atypical and histologically are characterized by architectural disorder and cytological atypia. Their diagnosis is reproducible if criteria and thresholds are agreed upon. They are significant only in relation to melanoma, as simulants of melanoma, as markers of individuals at increased risk of developing melanoma, and as potential and occasional actual precursors of melanoma. Morphologically and biologically, they are intermediate between common naevi and melanoma. Individuals with dysplastic naevi may have deficient DNA repair, and dysplastic naevi lesions are associated with overexpression of pheomelanin, which may lead to increased oxidative damage and increased potential for DNA damage and tumour progression.

Pigmented lesion pathology: what you should expect from your pathologist, and what your pathologist should expect from you

The first part of this review examines the reliability of histologic diagnosis in pigmented lesions, as measured by concordance studies and medicolegal analysis. It emphasizes the role of clinicians in maximizing that reliability, by providing adequate clinical descriptions, using appropriate biopsy technique, and critically interpreting pathology reports. It identifies those entities that are especially problematic, either because they cannot be reliably recognized by the histopathologist or because their histology is a poor guide to their biologic behavior. The second part of the review is a guide to some of the more difficult and controversial pigmented lesions, including dysplastic nevus, spitzoid nevi and melanomas, cellular blue nevus, animal-type melanoma, and deep penetrating nevus.

Dysplastic nevus: the eye of the hurricane

Dysplastic nevi were generally recognized, thanks to the contributions of Clark et al. in 1978. These lesions were described in a familial context, which was called the 'B-K mole syndrome'. However, it is worth noting that this was not the first time that these nevi had been described in the literature. If we look back in history, we can find that in 1820, Norris had already described some very similarly pigmented lesions, also in a familial context, just as Cawley subsequently did in 1952. Clark coined the term of dysplastic nevi for lesions presenting in patients with personal and family histories of malignant melanoma, having from 10 to 100 nevus lesions of a certain size, irregular shape and variable pigmentation of more than 5 mm. In addition, he pointed out that histologically, such lesions were principally characterized by the presence of atypical melanocytic hyperplasia.

A retrospective study addressed to understanding what predicts severe histological dysplasia/early melanoma in excised atypical melanocytic lesions

BACKGROUND

Atypical naevi are common benign skin lesions but are also recognized both as precursors of and risk factors for melanoma. It is therefore imperative to excise those lesions that are either likely to progress or are already progressing to melanoma. Clinically, however, it may be difficult to distinguish these from benign atypical naevi with bland histology.

OBJECTIVES

To analyse the clinical characteristics of excised melanocytic lesions and to identify the predictors of severe histological atypia/melanoma in situ and invasive melanoma.

METHODS

The case notes of 434 patients who had melanocytic lesions removed at a pigmented lesion clinic were studied retrospectively. A single pathologist reviewed the excised lesions and clinical characteristics predictive of malignancy were identified.

RESULTS

The best predictors of melanoma were older age, history of change and site on an extremity, but only older age was predictive of severe histological atypia/melanoma in situ as opposed to mild to moderate atypical histology.

CONCLUSIONS

These results confirm the difficulty of differentiating accurately between benign atypical naevi and borderline lesions or early melanoma in a clinical setting. It is therefore necessary to have a sufficiently low threshold for excision to avoid missing early melanomas, particularly in older patients presenting with lesions on the extremities.

Precursors to melanoma and their mimics: nevi of special sites

Melanocytic nevi, which are benign tumors of melanocytes, may have occasional cosmetic significance but, for the most part, they are important only in relation to melanoma. Nevi are the most important simulants of melanoma, both clinically and histologically, and can usually be reliably distinguished from melanomas using published criteria. Some lesions are characterized by greater degrees of atypia and may be more difficult to diagnose. Dysplastic nevi are among the most important simulants of melanoma. Nevi may also be important as potential precursors of melanoma; however, most nevi are stable and will not progress to malignancy. Nevi are vastly more common than melanomas and the rate of progression of individual lesions is very low. Therefore, nevi are not as a rule managed by wholesale excision to prevent melanoma. Nevi are also important as risk markers, identifying individuals at greater risk of developing melanoma in the future. Dysplastic nevi and, to a lesser extent, common acquired and congenital nevi are among the most important melanoma risk markers. Nevi of special sites have been identified as nevi that may show atypical features suggestive of a dysplastic nevus or of a melanoma. However, they are not risk markers and they are not malignancies. Nevi of genital skin, acral skin, and flexural skin are among the most important 'nevi of special sites'. It is important, in considering the differential diagnosis of a lesion in a special site, to avoid overcalling such a lesion as a melanoma or a dysplastic nevus because this could lead to excessive treatment. Conversely, it is important to avoid undercalling a lesion that is a dysplastic nevus or a melanoma as a nevus of special sites, because in this circumstance a patient could lose the opportunity either for surveillance to recognize a developing melanoma at an early, curable stage, or for definitive treatment of an established malignancy. In this monograph, dysplastic nevi and nevi of special sites are compared and contrasted in relation to melanoma.

The genetics of hereditary melanoma and nevi. 1998 update

Although the first English-language report of melanoma in 1820 contained a description of a melanoma-prone family, it was 1983 before formal genetic analysis suggested an autosomal dominant mode of inheritance for both melanoma and the then newly described melanoma precursor, dysplastic nevi (DN). Subsequent genetic studies have assumed this model to be correct, although when viewed in aggregate, the data are inconsistent. The first proposed melanoma gene (CMM1) was mapped to chromosome 1p36. This gene assignment has not been confirmed. A second melanoma gene, designated CMM2, has been mapped to chromosome 9p21. This gene assignment has been confirmed, and the cell cycle regulator CDKN2A has been proposed as the candidate gene. Germline mutations in this gene have been identified in about 20% of melanoma-prone families that have been studied to date. Pancreatic cancer occurs excessively in melanoma families with germline mutations in CDKN2A. Germline mutations in the cyclin-dependent kinase gene CDK4 (chromosome 12q14) have been described in three melanoma families. This finding represents a third melanoma gene but one that accounts for only a tiny fraction of all hereditary melanoma. Recently, a familial melanoma-astrocytoma syndrome has been reported. Large germline deletions of 9p21 occur in these families, with the p19 gene implicated in its pathogenesis. At present, clinical predictive genetic testing for mutations in the CDKN2A gene is available commercially, but its use has been limited by uncertainty as to how test results would affect the management of melanoma-prone family members. Currently, management recommendations include monthly skin self-examination, clinical skin examination once or twice yearly, a low threshold for simple excision of changing pigmented lesions, moderation of sun exposure, and appropriate use of sunscreens. A heritable determinant for total nevus number has been suggested by twin studies. Other data suggest the presence of a major gene responsible for "total nevus density" in melanoma-prone families. Approximately 55% of the mole phenotype in multiplex melanoma families was explained by this proposed gene. An autosomal dominant mode of inheritance has been proposed for DN, and data exist to suggest that DN may be a pleiotropic manifestation of the 1p36 familial melanoma gene. However, there clearly are melanoma-prone families that do not express the dysplastic nevus trait, and some of the families linked to CDKN2A also present with dysplastic nevi. Several studies have shown a surprisingly high prevalence of DN on the skin of family members of probands with DN. In light of the extensive evidence documenting that persons with DN (both sporadic and familial) have an increased prospective risk of melanoma, these family studies suggest that relatives of persons with DN should be examined for both DN and melanoma. Genetic determinants play a major role in the pathogenesis of normal nevi, DN, and melanoma. Identifying the molecular basis of these genetic events promises to enhance melanoma risk-reduction strategies and, ultimately, reduce melanoma-associated mortality.