TTF-1 is useful for primary site determination in duodenal metastasis.

We report here on a case of duodenal metastasis from primary lung adenocarcinoma. A 69-year old man was diagnosed with primary lung adenocarcinoma. Four courses of combined chemotherapy with carboplatin and paclitaxel associated with irradiation of 60 Gy shrunk the lung tumor. However, soon after,the para-aortic lymph node became swollen. Esophagogastroduodenoscopy revealed three duodenal tumors. Differential diagnosis between malignant lymphoma and metastatic duodenal cancer was endoscopically difficult. The histology of biopsied specimens was poorly differentiated adenocarcinoma. Immunohistochemical analysis revealed a positive reaction for thyroid transcription factor-1 (TTF-1). Thus, we concluded that these were metastatic duodenal tumors from lung adenocarcinoma. Two courses of gemcitabine led to a complete remission in this duodenal metastasis and para-aortic lymph node swelling with only scarring remaining in computed tomography. He is now on the continuous generalized chemotherapy. In conclusion, duodenal metastasis from primary lung adenocarcinoma is rare and hard to diagnose. In such an instance, TTF-1 immunostaining is crucial to obtain the correct diagnosis.