Intradermal Melanoma Associated With an Intradermal Melanocytic Nevus.

Intradermal melanoma on a pre-existing intradermal nevus is an exceptional finding. Since 1961, a total of 11 cases have been published; none of these were in the Spanish medical literature (PubMed, December 27, 2014). We report the case of a 42-year-old man who underwent treatment at his health center for a lesion in the center of his forehead. In the clinical history, the lesion was described as a fibroelastic nodule measuring 7mm in diameter. The patient reported that the lesion had been present since childhood and that it had grown progressively during the last year. The patient’s personal history contained no record of relevant disease, previous removal of cutaneous lesions, or family history of neoplasm. Histopathology revealed a nodular lesion (Fig. 1) composed of an intradermal melanocytic nevus in contact with the surgical margins (Fig. 2) at the center of which was a nodule whose larger diameter measured 5mm. The nodule was composed of atypical melanocytes. Additional histopathologic findings included cell pleomorphism, aberrant nucleoli, absence of maturation, isolated cellular necrosis, and 3 mitotic figures per square millimeter (Fig. 3A). No significant lymphocytic or junctional components were observed. The atypical cells showed intense cytoplasmic expression of S-100 and MelanA (diffuse) and HMB-45 (focal) (Fig. 3B). Physical examination revealed no further atypical pigmented lesions or enlarged lymph nodes. Extending the margins with a lateral 1-cm excision that reached the fascia only revealed scar fibrosis. Selective biopsy of the sentinel node was performed, and staining of several sections with hematoxylin-eosin, S-100, and HMB-45 revealed absence of tumor cells. Finally, the extension study ruled out metastasis of primary melanoma from another site. No significant findings were revealed by ultrasound scan (eyes, neck, and abdomen) or positron emission tomography with computed tomography. The results of the laboratory analysis were also unremarkable, with a normal S-100 protein concentration (0.05 g/L). The clinical, laboratory, and histopathology findings confirmed the diagnosis of melanoma developing from an intradermal nevus. The risk of progression to malignancy in benign melanocytic lesions was recently studied in a metaanalysis, which revealed a 2% incidence for melanoma, especially for congenital nevi > 40 cm located on the trunk. However, very few epidemiological data are available on intradermal melanoma arising from an intradermal nevus,