Giant metastatic malignant melanoma with an unknown primary site

We report a case of malignant melanoma of unknown primary origin which presented with a giant metastatic tumor in his right inguinal region. A 94-year-old man noticed a small subcutaneous tumor in the right inguinal region 3 years earlier, which eventually became as larger as 9 cm in diameter without treatment. Although a histological examination of the lesion showed malignant melanoma, extensive examination did not reveal its primary lesion or any metastasis other than that to the right inguinal area. Our case took an interesting course in that this well-growing metastatic tumor was localized in only one region and supported a previous report indicating that malignant melanoma with unknown primary origin has a low tendency to metastasize and a relatively good prognosis.