Tumor-to-Tumor Metastasis: Renal Cell Carcinoma Metastasizing to a Lipoma of the Thigh

A 73-year-old man with a medical history significant for renal cell carcinoma (RCC) presented with widespread osseous metastases and imaging suspicious for RCC metastasizing to a lipoma interdigitated within the right vastus lateralis. The patient's pathological fractures were surgically addressed, and the lipoma excised. Final histology revealed a thigh lipoma involved by metastatic RCC without direct extension.Tumor-to-tumor metastasis is a rare occurrence, with RCC typically being the most common "recipient" tumor. This is the first case to the best of our knowledge of RCC metastasizing to a lipoma, highlighting a rare phenomena in a patient with metastatic disease.