Synchronous tumors are defined as two tumors arising concurrently or within six months of each other. Reports of synchronous RCC and breast cancer are limited to nonmetastatic renal cell carcinoma (RCC) and hormone receptor-positive infiltrative ductal carcinoma. We present the first case of synchronous metastatic renal cell carcinoma and metastatic triple-negative breast cancer, managed with a novel combination of immunotherapy and chemotherapy.