Cutaneous metastasis of renal cell carcinoma: an electron microscopic study.

A case of cutaneous metastasis of renal cell carcinoma in a 67-year-old man is described. Right side nephrectomy had been performed three years earlier, and a renal cell carcinoma was diagnosed. Following a bruise, the patient noticed an erythematous nodule on the scalp. Histological examination of this skin lesion showed atypical tumor cells consisting predominantly of clear cells with a honeycomb-like or adenoid structure. Electron microscopic examination revealed that the tumor cells were divided into three groups: clear cells with abundant glycogen, dark cells with abundant mitochondria, and intermediate cells containing both glycogen and mitochondria in varying proportions. Some of the tumor cells with an adenoid pattern had a brush border-like structure in the lumen. These results support the diagnosis of metastatic renal cell carcinoma. An electron microscopic approach may aid in diagnosis of cutaneous metastasis from renal cell carcinoma.