Critical analysis of histologic criteria for grading atypical (dysplastic) melanocytic nevi

Analysis of interobserver reproducibility in grading dysplastic nevi: Results of the application of the 2018 World Health Organization grading criteria

BACKGROUND

We aimed to determine whether the histopathological grading of dysplastic nevi is an objective endeavor, considering interobserver variability, according to 2018 World Health Organization (WHO) criteria.

METHODS

In total, 179 cases of dysplastic nevi, with high and moderate degree of atypia, diagnosed and graded according to the previous criteria were reviewed by three pathologists. Then, the observers graded the dysplastic nevi as low or high according to 2018 WHO criteria.

RESULTS

Grading of dysplastic nevi was in complete agreement in 99 out of 179 cases across three observers with a fair level of overall interobserver agreement (multirater κ_free : 0.40). The observers showed moderate to good agreement for most of the architectural features, except for criteria regarding focal continuous basal proliferation of melanocytes, density of non-nested junctional melanocytes, and presence of dyscohesive nests of intraepidermal melanocytes, whereas fair agreement was achieved for the cytological criteria.

CONCLUSIONS

The 2018 WHO criteria for dysplastic nevus will ensure a common approach to the diagnosis and grading of dysplastic nevi. However, histopathological criteria, such as cytological features and focal continuous basal proliferation of melanocytes, should be improved so as to ensure a more accurate surgical approach and risk assessment.

Parakeratosis and pagetoid melanocytosis in the evaluation of dysplastic nevi and melanoma

BACKGROUND

It is our experience that parakeratosis with pagetosis is common in early melanoma when there is no history of trauma in the anatomical site. In lesions where the differential diagnosis includes dysplastic nevus (DN) and melanoma, we hypothesize that parakeratosis may be a marker for cases in which immunohistochemistry (IHC) may identify occult pagetosis.

METHODS

We performed a retrospective case-control study on cases with a histologic differential diagnosis of DN versus melanoma, including 423 cases with parakeratosis and 125 cases without parakeratosis. IHC staining (Mart-1 and/or Sox-10) was performed in all cases. The frequency of pagetosis and diagnostic upgrades in the cases versus the controls was calculated.

RESULTS

The presence of parakeratosis was significantly associated with pagetosis (p < 0.0001). Diagnostic upgrades were more frequent in the cases with parakeratosis versus controls without parakeratosis (p = 0.0029). In the favored moderate DN group, 56% of cases were upgraded compared to 30% of the controls (p = 0.0017). In the favored mild DN and severe DN groups, there were more case upgrades compared to the controls (p = 0.1386, p = 0.2738).

CONCLUSIONS

Parakeratosis may be a useful marker to identify lesions with occult pagetosis for which IHC would be appropriate and may result in a diagnostic upgrade.

The role of reflectance confocal microscopy in differentiating melanoma in situ from dysplastic nevi with severe atypia: A cross-sectional study

BACKGROUND

Melanoma in situ and dysplastic nevi with severe atypia present overlapping histopathologic features. Reflectance confocal microscopy findings can be integrated with the dermatopathology report to improve differentiation between melanoma and dysplastic nevi with severe atypia.

OBJECTIVE

To compare prevalence of reflectance confocal microscopy findings between melanoma in situ and dysplastic nevi with severe atypia.

METHODS

This retrospective observational study compared reflectance confocal microscopy findings in dermatopathologically diagnosed dysplastic nevi with severe atypia and melanoma in situ, collected between 2007 and 2017 at a private pigmented-lesion clinic. Concordant pathologic diagnosis was defined as unanimous agreement between 3 dermatopathologists who independently reviewed all cases; all other cases were classified as discordant.

RESULTS

The study included 112 lesions, 62 concordant melanomas in situ, 28 concordant dysplastic nevi with severe atypia, and 22 discordant lesions. In comparing reflectance confocal microscopy findings in concordant cases, melanoma in situ showed more frequently than dysplastic nevi with severe atypia the presence of epidermal atypical melanocytes as round cells (19/62 vs 0/28; P < .001) and dendritic cells (50/62 vs 6/28; P < .001), as well as a diffuse distribution of epidermal atypical melanocytes (50/54 vs 3/6; P = .002). In contrast, dysplastic nevi with severe atypia showed the presence of dense melanocytic nests more frequently than melanoma in situ did (15/28 vs 14/62; P = .003).

LIMITATIONS

The study was based on a limited number of lesions originating from a single clinic.

CONCLUSIONS

Reflectance confocal microscopy findings may help differentiate a subset of dysplastic nevi with severe atypia from melanoma in situ.

Common and not so Common Melanocytic Lesions in Children and Adolescents

The acquired melanocytic nevus is the most common lesion encountered by pediatric pathologists and dermatopathologists in their daily practice. In most cases, there are few difficulties in histopathologic diagnosis. However, it is the acquired melanocytic lesion known as the Spitz nevus, with its intrinsic atypical features which becomes the challenge since it exists along a histopathologic and biologic continuum from the atypical Spitz tumor to spitzoid melanoma. The frustration with some of these spitzoid lesions is that even the "experts" cannot agree as to the differentiation of one from the other even at the level of molecular genetics. Other melanocytic lesions are discussed including the congenital melanocytic nevus with its proliferative nodule(s) and melanoma as the ultimate complication. Although uncommon, cutaneous melanoma in the first 2 decades is emerging as a clinical problem especially in young women in the second decade of life. These are ultraviolet-associated neoplasms whose histopathologic and prognostic features are identical to the adult experience. Considerable progress has been made over the past 15 to 20 years in our understanding of cutaneous melanocytic lesions, but gaps still exist in the important group of spitzoid lesions. It can also be anticipated that more cutaneous melanomas in children will be seen in the future based upon epidemiologic studies.

Familial atypical multiple mole melanoma (FAMMM) syndrome: history, genetics, and heterogeneity

Approximately 5-10 % of cutaneous melanoma occurs in kindreds with a hereditary predisposition. Mutations in the CDKN2A gene are found to occur in approximately 20-40 % of these kindreds. The first historical mention of what is now called the familial atypical multiple mole melanoma syndrome appears to be from 1820, with more reports throughout the 1950s, 1960s, and later years. In 1991, Lynch and Fusaro described an association between familial multiple mole melanoma and pancreatic cancer and work continues to elucidate the syndrome's genotypic and phenotypic heterogeneity. Individuals at risk for familial melanoma need periodic screenings. Unfortunately, adequate screening for pancreatic cancer does not currently exist, but pancreatic cancer's prominence in the hereditary setting will hopefully act as a stimulus for development of novel screening measures.

Histologic Spectrum of Melanocytic Nevi Removed from Patients > 60 Years of Age

Background:

The histology of melanocytic nevi removed from older patients often differs from that of nevi from younger adults. According to the literature, the most common nevus in older individuals is the intradermal nevus, and purely junctional nevi are rare and should alert the pathologist to a possible melanoma precursor.

Objective:

To evaluate the histologic features of melanocytic nevi removed from patients > 60 year of age.

Methods:

Biopsies of nevi ( N = 215) from 172 patients > 60 years (mean age 69 ± 7 years) were examined retrospectively by three dermatopathologists, a consensus diagnosis was rendered, and the spectrum of histologic features was documented.

Results:

Junctional melanocytic nevi were frequently diagnosed in older patients (21% of cases) and a lentiginous, often heavily pigmented growth pattern was common (12% of nevi). Severely atypical (dysplastic) changes were found in 6% of nevi removed from older patients.

Conclusions:

We conclude that benign junctional nevi are relatively common in older patients and that a lentiginous, heavily pigmented growth pattern, traditionally associated with younger individuals, is often seen in both junctional and compound nevi in this older age group. This pattern must be differentiated from dysplastic nevus and melanoma in situ, which they may clinically resemble.

[Dysplastic melanocytic nevus]

Dysplastic nevus is still a controversial entity both clinically and histologically. The occurrence of dysplastic nevus especially in the context of dysplastic nevus cell syndrome is associated with an increased risk for melanoma. The following minimal histological criteria should be fulfilled: nests of melanocytes varying in size and shape, bridging and confluent, proliferation of single melanocytes basal and suprabasal, cytoplasmic and nuclear atypia of melanocytes and subepidermal fibroplasia. The biological behavior (common nevus variant or precursor of melanoma?) is difficult to evaluate by presently available methods. The further development of new molecular biology techniques may allow a better prognosis of dysplastic nevi in an objective and reproducible manner. Against this background complete excision followed by clinical surveillance has to be recommended for the routine practice.

NRAS and BRAF mutations in melanoma-associated nevi and uninvolved nevi

According to the prevailing multistep model of melanoma development, oncogenic BRAF or NRAS mutations are crucial initial events in melanoma development. It is not known whether melanocytic nevi that are found in association with a melanoma are more likely to carry BRAF or NRAS mutations than uninvolved nevi. By laser microdissection we were able to selectively dissect and genotype cells either from the nevus or from the melanoma part of 46 melanomas that developed in association with a nevus. In 25 cases we also genotyped a control nevus of the same patients. Available tissue was also immunostained using the BRAF^V600E-mutation specific antibody VE1. The BRAF^V600E mutation was found in 63.0% of melanomas, 65.2% of associated nevi and 50.0% of control nevi. No significant differences in the distribution of BRAF or NRAS mutations could be found between melanoma and associated nevi or between melanoma associated nevi and control nevi. In concordant cases immunohistochemistry showed a higher expression (intensity of immunohistochemistry) of the mutated BRAF^V600E-protein in melanomas compared to their associated nevi. In this series the presence of a BRAF- or NRAS mutation in a nevus was not associated with the risk of malignant transformation. Our findings do not support the current traditional model of stepwise tumor progression.

The dysplastic nevus: from historical perspective to management in the modern era: part I. Historical, histologic, and clinical aspects

Since its description in the 1970s, the dysplastic nevus has been a source of confusion, and whether it represents a precursor to melanoma remains a controversial subject. Although a Consensus Conference in 1992 recommended that the term "dysplastic nevus" no longer be used, the histologic diagnosis continues to present a therapeutic quandary for dermatologists and other physicians, and there remains significant variation in clinical management. In part I of this continuing medical education review, we will discuss the historical origins of the term, the evidence for its distinct histologic basis, and its clinical significance.

The pathology of melanoma

Although melanoma represents only 10% of all skin cancer diagnoses, it accounts for at least 65% of all skin cancer-related deaths. The number of new cutaneous melanoma cases projected during 2010 was 68,000-a 23% increase from the 2004 prediction of 55,100 cases. In 2015, the lifetime risk of developing melanoma is estimated to increase to 1 in 50. As the incidence of melanoma continues to rise, now more than ever, clinicians and histopathologists must have familiarity with the various clinical and pathologic features of cutaneous melanoma.

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.

Heterogeneous topographic profiles of kinetic and cell cycle regulator microsatellites in atypical (dysplastic) melanocytic nevi

Atypical (dysplastic) melanocytic nevi are clinically heterogeneous malignant melanoma precursors, for which no topographic analysis of cell kinetic, cell cycle regulators and microsatellite profile is available. We selected low-grade atypical melanocytic nevi (92), high-grade atypical melanocytic nevi (41), melanocytic nevi (18 junctional, 25 compound) and malignant melanomas (16 radial growth phase and 27 vertical growth phase). TP53, CDKN2A, CDKN1A, and CDKN1B microsatellite patterns were topographically studied after microdissection; Ki-67, TP53, CDKN2A, CDKN1A, and CDKN1B expressions and DNA fragmentation by in situ end labeling for apoptosis were topographically scored. Results were statistically analyzed. A decreasing junctional-dermal marker expression gradient was observed, directly correlating with atypical melanocytic nevus grading. High-grade atypical melanocytic nevi revealed coexistent TP53-CDKN2A-CDKN1B microsatellite abnormalities, and significantly higher junctional Ki67-TP53 expression (inversely correlated with CDKN1A-CDKN1B expression and in situ end labeling). Malignant melanomas showed coexistent microsatellite abnormalities (CDKN2A-CDKN1B), no topographic gradient, and significantly decreased expression. Melanocytic nevi and low-grade atypical melanocytic nevi revealed sporadic junctional CDKN2A microsatellite abnormalities and no significant topographic kinetic differences. High-grade atypical melanocytic nevi accumulate junctional TP53-CDKN1A-CDKN1B microsatellite abnormalities, being progression TP53-independent and better assessed in the dermis. Melanocytic nevi and low-grade atypical melanocytic nevi show low incidence of microsatellite abnormalities, and kinetic features that make progression unlikely.

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.

The "dysplastic" nevus

Dysplastic nevi have become an increasing focus clinically, with evidence that they are associated with a higher risk of developing melanoma. However, there still is contention regarding the significance of dysplastic nevi. This contribution provides an overview of the history, epidemiology, genetics, clinical and histologic features, and procedures for clinical management of dysplastic nevi. Since dysplastic nevi were described originally in 1978, a great deal of research has examined the epidemiology of these lesions and the genetic factors related to the development of dysplastic nevi. However, there is disagreement regarding the clinical management of dysplastic nevi and the histologic definition of dysplastic nevi. Current recommendations include preventative measures, such as sun protection and careful surveillance and biopsies of suspicious lesions as needed. The advent of new technologies, such as computer-vision systems, have the potential to significantly change treatment of dysplastic nevi in the future.

Expression of gamma-H2AX in melanocytic lesions

gamma-H2AX is a marker of activated DNA damage and is overexpressed in many malignancies and their precursor lesions. Previous studies have demonstrated the expression of gamma-H2AX in melanoma and dysplastic nevus, but its diagnostic and prognostic utility in a full range of melanocytic lesions has not been fully studied. In the current study, we investigated gamma-H2AX expression in a total of 162 melanocytic lesions. We found that gamma-H2AX was observed at higher levels (percentage and intensity of staining) in melanoma in situ (12/13), primary cutaneous melanoma (32/33; with the exception of desmoplastic melanoma), and metastatic melanoma (58/62), which was statistically different from that in benign nevus (7/9), dysplastic nevus (6/10), and Spitz nevus (5/9) considered together (P < .0001). Of note, desmoplastic melanoma (20/26) demonstrated weak or negative gamma-H2AX staining. The expression of gamma-H2AX did not show significant correlation with many melanoma prognostic factors, including Breslow depth, mitotic rate, and sentinel lymph node status. Except for desmoplastic melanoma, no difference in gamma-H2AX levels was observed among various melanoma subtypes. The overexpression of gamma-H2AX in melanoma as opposed to nevus indicates its possible role in melanomagenesis. Based on the overlap in subsets of nevi and melanomas, the potential clinical utility of this antibody remains uncertain until further studies have been carried out in a larger cohort of melanocytic lesions, including borderline cases.

Hereditary cancer syndrome diagnosis: molecular genetic clues and cancer control

Oncologists who are aware of the progress in hereditary cancer syndrome diagnosis, and, in particular, of how this effort may be effectively facilitated through a comprehensive family history in concert with molecular genetic studies, are in the envious position of designing highly targeted screening and management programs for the membership of these cancer-prone families. The Lynch syndrome is discussed as a clinical model wherein the presence of mismatch repair mutations provides a high level of diagnostic certainty for the initiation of targeted cancer screening and management. The familial atypical multiple mole melanoma-pancreatic cancer (FAMMM-PC) syndrome, on the other hand, provides another model with cancer-control potential. Given its phenotypic features of multiple atypical nevi, high total body mole count and cutaneous malignant melanoma, coupled with the integral association of PC in a subset of FAMMM kindreds with the CDKN2A germline mutation, this may result in a perhaps lower level of diagnostic certainty when compared with the Lynch syndrome. This knowledge may impact upon progress in the earlier diagnosis of melanoma and provide an impetus for creative diagnostic methods in PC, a disease that, at this time, demonstrates a mortality rate virtually identical to its incidence rate.

Cytoarchitectural and kinetic features in the histological evaluation of follicular thyroid neoplasms

AIMS

The diagnosis of follicular thyroid carcinomas is mainly based on capsular and vascular invasion. The aim of this study was to determine the diagnostic relevance of nuclear features, inflammation and stromal changes.

METHODS AND RESULTS

Anisokaryosis, chromatin pattern, nucleolus, nuclear pleomorphism, nuclear/cytoplasmic ratio, necrosis, stromal changes and tumour interstitial lymphocytes (TIL) were analysed in adenomatous hyperplastic nodules (39), adenomas (43) and carcinomas (28 minimally invasive, 48 widely invasive and 27 anaplastic). Ki67 immunostaining, in situ end labelling (ISEL) for apoptosis and the Ki67/ISEL index were analysed by topographical compartments. Variables were compared by histological diagnosis using Fisher's exact test, analysis of variance and Student's t-tests and considered significant if P < 0.05. TIL were absent in 96% of neoplasms and 54% of adenomatous hyperplastic nodules. Conspicuous nucleoli, increased nuclear-cytoplasmic ratio and coexistent apoptosis-myxoid changes distinguished minimally invasive carcinomas from adenomas. The most specific variables of high-grade carcinoma were vasculonecrotic patterns, nuclear hyperchromatism and pleomorphism. A kinetic advantage predominated in the internal compartments of benign lesions and in the peripheral compartments of malignant lesions.

CONCLUSIONS

Follicular carcinomas show up-regulation of proliferation markers and the distinctive topographical kinetic profiles provide a basis for the distinction between benign and malignant and an explanation for the circumscription and encapsulation of benign lesions.

Cyclooxygenase-2 (COX-2): first immunohistochemical marker distinguishing early cutaneous melanomas from benign melanocytic skin tumours

We have reported recently that changes in expression level of COX-2 are correlated with development and progression of human melanoma. In this study, we investigated whether the COX-2 expression level might be a useful immunohistochemical marker for distinguishing cutaneous melanomas from benign melanocytic lesions. Up to now, immunohistochemical markers have not ensured satisfactory sensitivity and specificity of differential pathologic diagnosis of melanoma. The expression of COX-2 was determined immunohistochemically in formalin-fixed, paraffin-embedded specimens of 33 early Clark I/II melanomas and 58 naevi. Mean COX-2 expression in melanomas was significantly stronger than in naevi (P approximately 10(-13)). A simple diagnostic algorithm using threshold values of the COX-2 expression level allows for differentiation between early melanomas and naevi with high sensitivity (Se) and specificity (Sp) (for Se between 91 and 100%, Sp values change between 96.5 and 51.7%). Areas under the receiver operating characteristic curves were, respectively, 0.97+/-0.02 and 0.86+/-0.04 for the COX-2 expression in central and border regions of the lesions. For all the melanomas (not only the early ones),the respective areas under the ROC curve values were 0.98+/-0.01 and 0.97+/-0.02. In conclusion, COX-2 is the first immunohistochemical marker that allows the distinguishing of early melanomas from benign melanocytic lesions with both high sensitivity and specificity.

Reliability of the histopathologic diagnosis of keratinocyte carcinomas

OBJECTIVE

We sought to determine the interobserver reliability of the histopathologic diagnosis of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) (keratinocyte carcinomas) in the setting of a Department of Veteran Affairs multicenter chemoprevention study.

METHODS

Interobserver concordance was assessed by blinded review of histopathologic slides by study dermatopathologists.

RESULTS

Overall interobserver agreement between the two dermatopathogists was kappa = 0.69 (95% confidence interval [CI] 0.67-0.69). The dermatopathologists' interobserver agreement was highest for basal cell carcinoma at kappa = 0.88 (95% CI 0.84-0.91) and for a diagnostic category in the SCC-actinic keratosis spectrum at kappa = 0.80 (95% CI 0.73-0.86). The largest disagreements between the two reference dermatopathologists were regarding the categories of invasive SCC at kappa = 0.62 (95% CI 0.52-0.72), SCC in situ at kappa = 0.42 (95% CI 0.29-0.56), and actinic keratosis at kappa = 0.51 (95% CI 0.40-0.62). Agreement between the local pathologists and central reference dermatopathologists were similar to the agreement between the central dermatopathologists. The morphea subtype of basal cell carcinoma was the only reliably diagnosed subtype (kappa = 0.79, 95% CI 0.51-1.00), and tumor depth was reliably measured.

LIMITATIONS

A limitation of this study was the use of only two reference dermatopathologists.

CONCLUSION

Because of the impact on physician decision making and patient care, researchers and clinicians need to be aware of reliability of histopathology results, particularly pertaining to the SCC and actinic keratosis spectrum.

Histologic similarities between lentigo maligna and dysplastic nevus: importance of clinicopathologic distinction

BACKGROUND

Lentigo maligna (LM) can histologically simulate dysplastic nevus (DN). Partial biopsy of LM may lead to misdiagnosis.

METHODS

One hundred and fourteen cases of LM and LM melanoma (LMM) were diagnosed at the Veterans Affairs Palo Alto Health Care System (1993-2002). Biopsy and excision specimens for 68 in situ and 28 invasive melanomas were classified as having predominant classical LM features, predominant DN-like morphology, or a mixed pattern.

RESULTS

Biopsy specimens demonstrated a predominant classical pattern in 38% (25/65) LM and 36% (10/28) LMM, predominant DN-like features in 43% (28/65) LM and 25% (7/28) LMM, and mixed pattern in 15% (10/65) LM and 29% (8/28) LMM. Most LM and LMM biopsies were partial. Significant DN-like features were present in 51% LM and 57% LMM excision specimens. Median age was 72 years for LM and 73 years for LMM, mean lesion diameters were 1.3 and 1.7 cm for LM and LMM, respectively, and 85% of LM and 75% of LMM cases were located on heavily sun-exposed sites.

CONCLUSIONS

Misdiagnosis of LM or LMM as DN could have devastating results. Large pigmented lesions on sun-damaged skin in elderly individuals should warrant consideration of LM/LMM diagnosis, even in the setting of DN-like features histologically. Excisional biopsy may help to avoid misdiagnosis.

My approach to atypical melanocytic lesions

Histological assessment of melanocytic naevi constitutes a substantial proportion of a dermatopathologist's daily workload. Although they may be excised for cosmetic reasons, most lesions encountered are clinically atypical and are biopsied or excised to exclude melanoma. Although dysplastic naevi are most often encountered, cytological atypia may be a feature of several other melanocytic lesions, including genital type naevi, acral naevi, recurrent naevi, and neonatal or childhood naevi. With greater emphasis being given to cosmetic results, and because of an ever increasing workload, several "quicker and less traumatising" techniques have been introduced in the treatment and diagnosis of atypical naevi including punch, shave, and scoop shave biopsies. A major limitation to all of these alternatives is that often only part of the lesion is available for histological assessment and therefore all too frequently the pathologist's report includes a recommendation for complete excision so that the residual lesion can be studied. Complete or large excision of all clinically atypical naevi permits histological assessment of the entire lesion, and in most cases spares the patient the need for further surgical intervention.

Common and uncommon variants of melanocytic naevi

Numerous variants of melanocytic naevi have been described. Their main pathological significance lies in their distinction from melanoma, as well as being precursors and risk markers for melanoma. Various degrees of atypia such as cytological atypia, architectural disorder and pagetoid spread (pagetoid melanocytosis) may be present in naevi and need to be recognised as appropriate for the subtype. As well as the distinction from melanoma, naevi must be differentiated from atypical lesions, such as atypical Spitz tumours, which do not fulfil all the criteria of melanoma, may be benign or malignant and have been called 'melanocytic tumours of unknown malignant potential'. The diagnostic grey area also includes a group of benign atypical naevi which are difficult to subclassify into specific entities. In this paper naevi are divided into: firstly, the common acquired group with a brief discussion of junctional, compound and intradermal naevi, minor variants such as halo and balloon naevi and the major variants that may cause problems -- dysplastic naevi, naevi of special sites, recurrent naevi and Spitz naevi; secondly, congenital naevi; thirdly, blue naevi and related lesions (dermal melanocytoses); and finally, combined naevi. The emphasis is on diagnostic pathological features and the differential diagnosis with melanoma.

Pitfalls in the diagnosis of malignant melanoma: findings of a risk management panel study

The misdiagnosis of melanoma is a major cause of malpractice claims involving pathologists and dermatologists. A detailed analysis of individual surgical pathology and cytology claims (excluding Pap smears) reported to The Doctors Company from 1995 through 2001 revealed that 46 of 362 claims (13%) involved the misdiagnosis of melanoma; 70% of these claims were for false-negative diagnoses. Melanoma claims were second only to claims involving breast biopsy. A Melanoma Risk Management Panel of expert dermatopathologists was convened to discuss recurrent "problem areas" identified by the author in claims reviewed from 1998 through 2001. The purpose was to devise useful strategies that pathologists and dermatologists could use in their practices to reduce the risk of diagnostic error and/or patient mismanagement when dealing with melanocytic lesions. The panel's findings and recommendations are the subject of this review.

Histopathological characteristics of small diameter melanocytic naevi

BACKGROUND/AIMS

The clinical definition of an atypical naevus ("dysplastic naevus" or "naevus with architectural disorder and cytological atypia of melanocytes") stresses size larger than 5 mm in diameter as a major diagnostic criterion. Because malignant melanomas and their precursors may arise in smaller lesions, a histological study of melanocytic lesions smaller than 4 mm in diameter was conducted to evaluate their histological appearance.

METHODS

Two hundred and sixty one naevi smaller than 4 mm in diameter were collected and characterised by histological examination into benign naevi without architectural disorder and naevi with architectural disorder and mild, moderate, and severe atypical melanocytes according to criteria used on larger lesions.

RESULTS

Small melanocytic naevi covered the same complex histological spectrum from benign naevi to severely atypical naevi when compared with larger lesions. A high proportion of small naevi (72%) exhibited features diagnostic for naevi with architectural disorder and cytological atypia.

CONCLUSION

There is a discrepancy between histological and clinically defined atypical naevi. The same generally accepted criteria for the histological diagnosis of atypical naevi should be used for small melanocytic naevi in addition to large ones. Thus, small naevi exhibiting atypical features on histological examination should be categorised as atypical naevi, regardless of their small diameter.

The 'common mole' from the point of view of digital dermoscopy analysis: subjective vs. objective evaluation of easy pigmented skin lesions

BACKGROUND

The term 'common mole', often used to describe a subset of benign pigmented skin lesions, is traditionally defined on the basis of morpho-chromatic features. In recent years, certain research groups have developed equipment and methods, such as digital dermoscopy analysis, that enable objective evaluation of pigmented skin lesions.

OBJECTIVE

In this study we use a digital dermoscopy analyser trained for the recognition of pigmented skin lesions to compare the subjective definition of 'common' and the mathematical concept of 'close to the mean of measurements'.

METHODS

A subset (100) of digital images of flat pigmented lesions, obtained in daily practice, were classified by trained and non-expert clinicians as common moles (60) or clear-cut melanoma (40), and processed with a DB-Mips analyser. The resulting parameters, validated by a classifier, were used to evaluate Hotelling's T2 multivariate distances from the mean.

RESULTS

'Common' moles could not be clearly defined in terms of closeness to the means of objectively evaluated parameters. Their diagnosis indudes many other evaluations and clusters of variables.

CONCLUSION

The clinical semantics of the term 'common' does not conform to any unambiguous mathematical definition.

The dilemma of the dysplastic nevus

There are few areas in dermatology that provoke as much controversy as dysplastic nevus. Over the past decade, there have been significant strides made in terms of understanding the biology and etiology of the lesion. Distinct and reliable clinical and histologic features have been delineated. In this article, the management of patients with dysplastic nevi and the role for dermoscopy, photographic surveillance, genetic mapping and counseling, chemoprevention, and nevi removal are discussed.

Immunohistochemical markers of melanocytic lesions: a review of their diagnostic usefulness

We critically reviewed recent literature reports of 25 melanocytic immunohistochemical markers. This review organizes and summarizes the many new studies of old and novel melanocytic markers and identifies the most promising diagnostic immunohistochemical markers that can be used to distinguish melanocytic from nonmelanocytic lesions and benign melanocytic from malignant melanocytic lesions.