Lung adenocarcinoma metastasizing into a renal angiomyolipoma

Tumor-to-tumor metastasis is a very rare phenomenon. The most common donor and recipient of tumor-to-tumor metastasis are carcinomas of lung and renal cell carcinoma, respectively. We report a case of primary lung adenocarcinoma that metastasized into a renal angiomyolipoma 9 years after the resection of primary lung tumor. Comparisons in morphology, immunohistochemical profiles, and genetic mutations indicate that the tumor metastasizing into angiomyolipoma originated from the same clone of previous lung adenocarcinoma. Albeit rare, pathologists should be aware of the possibility of tumor-to-tumor metastasis when confronting a neoplasm exhibiting 2 distinct morphological features.