Metastatic myxoid melanoma with partial regression of the primary lesion.

Myxoid melanoma is a rare variant of malignant melanoma. The diagnostic problems are obviously increased when it presents as amelanotic metastasis in a lymph node. An 82-year-old woman presented a subcutaneous mass in the right axilla. A thorough clinical investigation disclosed a pigmented black lesion on the right forearm. The right axillary lymph nodes and the pigmented lesion were resected. In the lymph nodes, proliferation of tumor cells with an abundant mucous substrate was noted. The cells proliferated in a variable pattern, and there were no melanin granules detected on hematoxylin-eosin-stained sections. However, we found melanin granules in the tumor cells observed under electron microscopy. In the pigmented lesion of the right forearm, there were small clusters of tumor cells with melanin granules, suggesting malignant melanoma. In the present case, myxoid metastasis occurred with the partial spontaneous disappearance of the primary nonmyxoid malignant melanoma.