264 Isolated Kidney Metastasis From Primary Lung Cancer: A Rare Phenomenon Causing Potential Diagnostic Pitfall

Abstract Introduction Common organs harboring metastatic non-small cell lung carcinomas (NSCLCs) include brain, bone, mediastinal lymph nodes, and intrapulmonary metastases. Other organs may be involved in advanced stage, in which renal metastasis is rather uncommon. Here we report a case of an isolated renal metastasis of NSCLC. Presentation of Case The patient is a 58-year-old woman who was initially diagnosed with T2bN0 lung adenocarcinoma in 2012 (5.5 cm). The tumor was completely resected, and no lymphovascular invasion was identified then. Four years later, the patient presented with fever, flank pain, and weight loss. CT scan revealed a single mass on left kidney mid to lower pole. No other lesions are identified by CT/PET. Biopsy showed malignant epithelial proliferation forming small glands and tubules with stromal desmoplasia. Collecting duct carcinoma (CDC) is suspected because of the morphology. However, grossly the tumor grows in cortex and is not originated from renal pelvis as CDC is. Microscopically tumor cells are infiltrative and dissecting through benign glomeruli and renal tubules. Both features are not typical for CDC or other primary renal tumors. Because of the patient’s history, immunohistochemical studies are performed to reveal the tumor is immunoreactive for TTF-1, but negative for PAX-8 and p63, confirming the metastatic disease. Eventually, nephrectomy was performed to release symptom and showed similar morphology. Discussion Only three cases of isolated renal metastasis of lung adenocarcinoma have been reported in literature. Primary renal epithelial tumors, especially CDC, are top differential diagnoses. Subtle gross and microscopic findings as illustrated above are helpful; however, ultimately awareness of patient’s relevant history is the key.