Metastatic chest wall tumor suspected to be of lung origin by immunoreactivity for cytokeratin 7 and 20.

We report a rare case of unknown primary carcinoma. A 36-year-old man was admitted to the hospital because of a chest wall tumor. Serum carcinoembryonic antigen level was 160 ng/ml. The resected chest wall tumor was pathologically diagnosed as metastatic adenocarcinoma, showing positive immunoreactivity for cytokeratin 7 and negative immunoreactivity for cytokeratin 20, suggesting lung origin. Serum carcinoembryonic antigen level returned to normal limits. Twenty-one months later, a chest X-ray showed a nodular lesion in the left upper lobe and serum carcinoembryonic antigen level increased to 12.3 ng/ml. Left upper lobectomy was performed 23 months after chest wall resection. The resected tumor was pathologically diagnosed as primary lung adenocarcinoma, showing the same immunoreactivity as in the chest wall tumor. The combination of immunohistochemistry for cytokeratin 7 and 20 appeared to be a useful tool in determining the site of origin and helpful for premortem diagnosis of the origin of unknown primary carcinoma.