Renal metastasis from pulmonary adenocarcinoma: the pathologist's approach to an uncommon finding: case report and review of the literature.

We herein report an uncommon case of renal metastasis from the lung in a 72-year-old man who 2 years before underwent surgical treatment for a pulmonary adenocarcinoma. During follow-up, a computed tomography scan revealed the presence of a solid mass located in the right kidney. Histopathologic and immunohistochemical examination of the enucleated lesion demonstrated the renal localization of an adenocarcinoma of the lung. Clinically recognized renal metastatic lesions from pulmonary cancer are a rare finding with only 35 cases reported to date in the English literature, and renal localization of adenocarcinoma of the lung is extraordinarily uncommon. Together with suggestive clinical data and negativity for markers of adenocarcinomas of different origin, thyroid transcription factor-1, when positive, is considered to be the most reliable marker for the differential diagnosis.