Report Melanoma in association with acquired melanocytic nevus in Japan: a review of cases in the literature Y. Togawa 1 , MD, Y. Nakamura 1 , MD, PhD, N. Kamada 1 , MD, PhD, N. Kambe 1 , MD, PhD, Y. Takahashi 2 , MD, PhD, and H. Matsue 1 , MD, PhD Departments of 1 Dermatology, and 2 Pathology, Chiba University Graduate School of Medicine, Chiba, Japan Correspondence Yaei Togawa, MD Department of Dermatology Chiba University Graduate School of Medicine 1-8-1 Inohana Chuo-ku Chiba 260-8670 Japan E-mail: togawa-yk@faculty.chiba-u.jp Conflict of interest disclosures: None. Abstract Background Malignant melanomas clinically and/or histologically associated with melano- cytic 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 melano- mas 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. Introduction Melanoma has often been discussed in the context of its association with melanocytic nevi. For instance, Roses et al. reported that between 35 and 50% of malignant melanomas appeared on the trunk or extremities (exclud- ing the hands and feet) and were histologically associated with nevus cells. 1 Stolz et al. reported that 33 of 150 cases (22%) of malignant melanomas were associated with melanocytic nevi. 2 In a larger study, Ackerman reported that in his analysis of 75,000 cases of malignant melanomas in Caucasians, about 80% of cases arose de novo; approximately 20% of cases, most of which were located on the trunk and proximal extremities, developed in association with pre-existing melanocytic nevi. 3 Numerous other analyses regarding melanomas associated with congenital or acquired melanocytic nevi have been conducted worldwide; the frequency of cases in which melanomas were associated with melanocytic nevi ranged from 8.4–50%. 1–16 The two most commonly reported types of melanomas associated with melanocytic nevi were superficial spreading melanomas (SSMs) and nodular melanomas (NMs). Lentigo malignant melano- mas (LMMs) and acral lentiginous melanomas (ALMs) are rarely associated with melanocytic nevi. 1,4,5,7,15 We recently observed a Japanese case of a superficial spreading melanoma (SSM) associated with a melanocytic nevus on the trunk. Surprisingly, we did not find any reviews or statistical data in the Japanese literature that examined melanomas associated with melanocytic nevi, although we did find such information in the Western lit- erature. However, we did find sporadic case reports among Japanese sources. Therefore, we sought to present our case and conduct a literature search among Japanese sources for reports of melanomas associated with melano- cytic nevi. Materials and methods Case report An 85-year-old Japanese woman visited our hospital in October 2006 for a blackish pigmented macule on the chest. The lesion 1362 International Journal of Dermatology 2010, 49, 1362–1367 ª 2010 The International Society of Dermatology