We report a case of malignant blue nevus (MBN) of the vulva which led to an ovarian metastasis 15 years after the initial diagnosis. To our knowledge, this is the first report of MBN of the vulva. The patient was a 28-year-old woman with a nodule of the labia majora. The patient noted the lesion when she was 12 and stated it did not change at that time. The lesion had the histopathologic features of MBN and was characterized by a low mitotic rate but substantial cytologic atypia. No abnormality was noticed over a 15 year period of follow-up. Fifteen years after the initial diagnosis, vaginal examination and ultrasonography imaging showed a 6.5 cm solid ovarian tumor. Hysterectomy and bilateral salpingo-oophorectomy was performed. Histologic evidence of metastasis was identified in the ovary. Malignant blue nevus can lead to late metastasis and needs long-term follow-up, as do other types of melanoma. Despite low mitotic activity in a melanocytic lesion resembling cellular blue nevus, a careful assessment of cytologic atypia is necessary before ruling out malignancy.
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