Search

Acquired melanocytic nevi commonly appear after birth and increase in number during the second and third decades. They represent benign aggregations of nevus cells in the epidermis and dermis and are usually various shades of brown in color. It is important to differentiate them from malignant lesions such as melanoma and when in question biopsies are recommended for histologic examination. They appear in equal frequency in males and females and are occasionally removed for cosmetic reasons.

Melanocytic nevi are defined as benign hamartomatous lesions composed of melanocytes. Melanocytes are derived from the neural crest and migrate during embryogenesis to selected ectodermal sites, primarily the skin and the central nervous system, including the eyes and the ears; however, ectopic melanocytes have been found in other organs such as multiple locations of the gastrointestinal tract. Acquired melanocytic nevi commonly form during early childhood and their onset is believed, at least in some cases, to be a response to sun exposure. However genetic factors are also involved in the development of some types of acquired nevi. Melanocytic nevi are biologically stable, benign lesions but in some occasions they can be associated with melanoma. The frequency of transformation of a melanocytic nevus into melanoma varies widely in the literature, with some data suggesting that up to 40 % of melanomas are associated with a precursor nevus.

Acquired melanocytic lesions resembling malignant melanoma have been described in all major categories of Epidermolysis bullosa and referred to as "Epidermolysis bullosa nevi''. They easily induce to diagnostic error, although no malignant transformation has been reported. We report the development of a large acquired melanocytic nevus at a site of recurrent blisters in a 5-year-old child with Epidermolysis bullosa simplex. The global dermoscopic pattern was suggestive of benignity, and the histopathological findings were compatible with a compound melanocytic nevus. This is the first published case of Epidermolysis bullosa nevi in Brazilian literature. Despite their benign behavior, we emphasize the importance of regular clinical and dermoscopic monitoring, since a malignant course still cannot be totally excluded.

Background Malignant melanomas clinically and/or histologically associated with melanocytic nevi have been reported worldwide. Approximately 20% of malignant melanomas in Caucasians, most of which are found on the trunk and proximal extremities, develop in association with pre-existing melanocytic nevi. In Japan, however, over half of all melanomas are acral lentiginous melanomas (ALMs) on the hands and feet; melanomas on sun-exposed areas are seen less frequently in Japanese people than in Caucasians. As ALMs are not usually accompanied by melanocytic nevi and there have been no reviews of the literature or statistical data regarding Japanese cases of melanomas with melanocytic nevi, dermatologists in Japan have few opportunities to see melanomas associated with pre-existing melanocytic nevi. Methods Here we report a case of a superficial spreading melanoma that was formed on a melanocytic nevus on the trunk, and we review for the first time the case reports from the Japanese literature. Results and Conclusions With regard to the reported cases, melanomas associated with melanocytic nevi were mainly superficial spreading melanomas and nodular melanomas on the trunk or extremities; ALMs were rarely associated with nevi, indicating a trend similar to that observed in Caucasians. These findings suggest that the low frequency of associations between melanomas and melanocytic nevi in Japan reflects racial differences in the frequencies of each type of melanoma.

The prognosis of malignant melanoma has been improving recently in Japan. One of the possible explanations for the favorable prognosis observed in the past 2 decadesis the increase in the number of stage I and II cases of acral lentiginous melanoma. Concurrently with such a trend, melanoma in situ has also increased in incidence. We have experienced 40 cases of melanoma in situ in the past 25 years. A clinicaldiagnosis of melanoma in situ was made in 27 of 40 cases; in the remaining 7 were diagnosed as pigmented nail streaks and 6 as acquired melanocytic nevus. Of the 40 lesions, 250 ccurred on the acral regions, 8 on the face, 6 on the oral mucousmembrane, and the remaining one on the trunk. No cases involved the extremitiesother than hands and feet. There was no sex difference, but female cases were predominant in the lesions developing on the mucous membrane and face. Almost all histological specimens showed the lentiginous type of proliferation of tumor cells. Corresponding to the fact that ALM is the most common type in the Japanese, thepredisposing sites for melanoma in situ in Japan were also the acral regions.

Background: As the sole of the foot is the most prevalent site of malignant melanoma in non-Caucasians, early detection of the neoplasm at this anatomical site is very important. In our previous study, we proposed a clinical guideline that acquired melanocytic lesions on the sole larger than 7 mm in maximum diameter should be examined histologically. Methods: Eighty-one Japanese patients with the complaint of plantar pigmented lesions were screened at our dermatology clinic during 3 years using the 7-mm criterion. Results: Of the total 80 melanocytic lesions on the sole, 14 lesions were larger than 7 mm in maximum diameter, excluding congenital lesions. Diagnoses of the 14 “large” lesions were as follows: advanced malignant melanoma, 8 lesions; early malignant melanoma (malignant melanoma in situ), 1 lesion; acquired melanocytic nevus, 4 lesions, and volar melanotic macule, 1 lesion. Conclusions: The present study confirmed the validity of the 7-mm criterion for the early effective detection of plantar malignant melanoma.