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

Abstract

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.

Figure 1

Cytological specimen from the vaginal mucosa demonstrating loose aggregates of pleomorphic tumour cells. The tumour cells had relatively abundant lacy cytoplasm and granular hyperchromatic large nuclei, with occasional prominent nucleoli (original magnification, ×40; Papanicolaou stain).

Figure 2

Biopsied specimen from the vaginal tumour demonstrating diffuse infiltration of large pleomorphic or spindle shaped tumour cells. The tumour cells have large oval or pleomorphic hyperchromatic nuclei and eosinophilic cytoplasm (original magnification, ×40; haematoxylin and eosin stain).

Figure 3

Immunohistochemical staining with HMB-45 in the vaginal tumour tissue. Note the positive staining in the cytoplasm of the tumour cell (original magnification, ×100).