Small Renal Cell Carcinoma Presenting With Testicular Metastasis: A Rare Case of pT1a Disease With an Aggressive Clinical Course.

Testicular metastasis of a renal cell carcinoma (RCC) is extremely rare, particularly in the initial clinical presentation. Herein, we describe a unique case in which a small renal mass (pT1a RCC) initially manifested as a contralateral testicular metastasis. A 64-year-old man presented with a right intrascrotal mass. Radiology revealed multiple enlarged retroperitoneal lymph nodes and an 18-mm mass in the left kidney. Following right orchidectomy, the tumor was pathologically not of testicular origin but metastasis. Subsequently, the patient underwent robot-assisted left partial nephrectomy (RAPN) and para-aortic lymph node dissection. Histopathological analysis confirmed RCC with testicular metastasis (pT1aN1M1). Despite administration of two lines of systemic therapy, the patient died of metastatic disease 21 months after RAPN. To the best of our knowledge, this is the first documented case of a pT1a RCC presenting initially as a contralateral testicular metastasis. Our findings highlight the importance of considering metastatic RCC in the differential diagnosis of testicular masses.