Answer of Dermatopathology Case 66
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Abstract:
Precursors to melanoma and their mimics: nevi of special sites.Mod Pathol.2006 Feb;19 Suppl 2:S4-20.
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.
Nevi with site-related atypia: a review of melanocytic nevi with atypical histologic features based on anatomic site.J Cutan Pathol. 2008 Oct;35(10):889-98.
A subset of melanocytic nevi share features with melanoma and nevi with architectural disorder but are biologically inert and to date do not appear to portend an increased risk for the development of malignancy. These benign nevi with certain atypical histologic features cluster among specific anatomic sites and are thus designated nevi with site-related atypia. We categorize these lesions into four main groups: acral, genital, special site and conjunctival, based on anatomy and relative prevalence of specific atypical histologic features. As the literature and our recognition of these lesions continue to grow, our understanding of their biology has not kept pace.
Melanocytic lesions of the genital area with attention given to atypical genital nevi.J Cutan Pathol. 2008 Nov;35 Suppl 2:24-7.
Melanocytic lesions of the genital area are rare. They arise mainly in the vulva, although they can also occur less frequently in the perineum, mons pubis and male genitalia and represent 10-12% of pigmented lesions of White women. These pigmented lesions include melanocytic nevi, lentigines, melanocytic nevi with architectural disorder and atypia of melanocytes (dysplastic nevi) and melanomas with microscopic features similar to those seen elsewhere on the body. There is a small subset of benign nevi named atypical melanocytic nevi of the genital type (AMNGT) that occur in young women, with distinctive histologic features in some cases overlapping morphologically with those of melanoma. Thus, it is important to distinguish AMNGT from melanomas in terms of prognosis and treatment. We retrieved 58 cases of genital pigmented lesions diagnosed at our hospital from 1986 to 2008 to evaluate their clinicopathologic features with especial consideration to those cases with atypical features. Thirty-two cases (55%) were common nevi, 10 (17%) lentigines, 6 (10%) melanomas, 3 (5%) dysplastic nevi and 1 blue nevus. Six cases (10%) corresponded to AMNGT and were taken from women with a median age of 21 years. All cases showed symmetry, and the melanocytic proliferation was well demarcated at the lateral margins. The junctional component was very prominent and formed by round or fusiform nests with common retraction artifact and/or cellular dyshesion or as a single cell proliferation with mild (33%) to moderate (67%) cytologic atypia, focal pagetoid spread (17%) and a benign-appearing dermal component (83%) with maturation and dense eosinophilic fibrosis in the superficial dermis. Neither nuclear atypia of melanocytes in the superficial dermis nor dermal mitoses were observed. AMNGT were excised, and no recurrences were recorded in the follow up (median 10.5 years). Therefore, it seems that there is no evidence that AMNGT are precursors of dysplastic nevi or melanomas.
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