A primary amelanotic melanoma of the vagina, diagnosed by immunohistochemical staining with HMB-45, which recurred as a pigmented melanoma.

Usually, malignant melanoma is readily diagnosed by the presence of melanin granules. Although amelanotic melanoma contains a few melanin granules, it is often difficult to differentiate from non-epithelial malignant tumours. This report describes a case of amelanotic melanoma of the vagina, which was originally suspected to be a non-epithelial malignant tumour, but was subsequently correctly diagnosed by immunohistochemical staining with the HMB-45 antibody and for the S-100 protein. A light grey tumour with superficial ulceration was located in the upper third of the vagina. The patient was treated with irradiation followed by chemotherapy. Subsequently, the tumour disappeared and cytology was negative; thus, she achieved complete remission. However, 20 months after complete remission, the tumour recurred locally: the site had a grossly black appearance, which was pathognomonic for a malignant melanoma. Thus, HMB-45 and S-100 protein immunohistochemistry confirmed the diagnosis of amelanotic melanoma.