We report a case of amelanotic melanoma. A 56-year-old man had noticed a small nodule on his right medial plantar aspect of the foot about one year previously. Although he had tried to remove the nodule by pricking with a pin, it had continued to grow.
When he visited our hospital an September 2, 1998, the dome-shaped nodule measured 20×18mm. On closer examination, a small pigmented macule was observed in the periphery of the nodule. The right inguinal lymph nodes were swollen.
We excised the tumor with the presumptive diagnosis of squamous cell carcinoma or eccrine porocarcinoma, since the pigmented macule was faint that the diagnosis of melanoma could not be considered. Wide local excision (2cm margin) and inguinal lymph node biopsy were performed. However, the histopathological diagnosis was malignant melanoma, and lymph node biopsy revealed metastasis of melanoma (pT4aN1M0, Breslow's thickness 4.6mm, Clark level V, Stage III) . Right inguinal lymph node dissection and chemotherapy were added. Electronmicroscopic study revealed many melanosomes in the melanoma cells and confirmed the diagnosis. Amelanotic melanoma should be considered when a red nodule on the foot is examined. [Skin Cancer (Japan) 2000; 15: 53-56]
