Abstract Introduction/Objective While most pulmonary embolisms are composed of blood clot resulting from venous stasis, tumor embolism is rarely encountered. We describe an autopsy patient with an unexpected renal cell carcinoma (RCC) who expired after a massive tumor embolism to the pulmonary artery. Methods/Case Report A 56-year-old male presented with complaints of shortness of breath and was found to have a large right-sided pulmonary embolism with an incidental finding of a 9.0 cm right kidney mass on imaging. He was subsequently admitted for further management consisting of thrombo-aspiration. The procedure was largely unsuccessful and the patient’s respiratory status continued to decline and he subsequently expired. On autopsy, a 9.3 x 6.2 x 6.0 cm, yellow-tan, well-defined mass was discovered primarily in the lower pole of the right kidney with invasion into the hilar structures. The mass grossly appeared to be invading into the renal vein. Two large yellow-tan emboli were found to be causing significant obstruction of the inferior vena cava at the level of the right renal vein and in the right pulmonary artery. Microscopic evaluation revealed the kidney tumor to be consistent with renal cell carcinoma morphologically and immunohistochemically. Interestingly, all emboli discovered at autopsy are primarily composed of sheets of cells identical to the patient’s renal mass. It is therefore concluded that the patient’s kidney cancer invaded into the renal vein and embolized to the pulmonary artery, ultimately resulting in death. Results (if a Case Study enter NA) NA Conclusion Tumor embolism is a rare cause of death. Renal cell carcinoma is a relatively common neoplasm that has been described to present as a tumor thrombus in 13.3% of patients. Of these patients with RCC tumor thrombus, 1% embolize to the right atrium. Our case represents this rare phenomenon and demonstrates why it is crucial to confirm the contents of a pulmonary embolism, as not all are composed of blood components alone.