We report 5 cases of metastatic lung carcinoma to the skin. The 5 patients, 4 male and one female, ranged in age from 35 to 80 years. Clinical manifestations were intracutaneous or subcutaneous nodules, which were located on various sites: the head, trunk, and inguinal region and finger. Histologic examination revealed 3 cases of adenocarcinoma and 2 cases of small cell carcinoma. Duration between occurrence of skin metastasis and death was from 4 to 14 months. No expression of cytokeratin 20 (CK20) was observed in any cases. The results suggested that CK20 is a useful marker in the differentiation between merkel cell carcinoma and skin metastasis of small cell carcinoma, or between metastasis from the lung and that from the gastrointenstinal (GI) tract because merkel cell carcinoma and adenocarcinoma of GI tract express CK20 in general. [Skin Cancer (Japan) 2000; 15: 179-184]
