Eosinophilic renal cell carcinoma colliding with renal perivascular epithelioid cell tumor: a case report.

Background: Collision tumors frequently occur in the gastrointestinal tract; however, they rarely occur in the kidney. Furthermore, most cases of renal collision tumors involve chromophobe renal cell carcinoma and oncocytoma or clear cell carcinoma and angiomyolipoma; collisions between other tumor types are rare. Case presentation: We present a case of a 30-year-old woman with a renal collision tumor. The patient was hospitalized following the incidental detection of a left renal mass 3 years ago. A partial nephrectomy was performed to carefully excise the tumor using a pair of tissue scissors, ensuring a margin of 0.5-1 cm from the tumor edge. Postoperative pathology confirmed two distinct tumors within the mass - eosinophilic renal cell carcinoma and renal perivascular epithelioid cell tumor. During follow-up, no signs of recurrence or distant metastases were noted. Conclusion: Renal collision tumors are infrequent and often present with nonspecific clinical signs. A definitive diagnosis is contingent on histopathological examination. Radiotherapy and chemotherapy remain essential when collision tumors harbor malignant components. For benign or less aggressive tumors, the primary strategy is surgical resection with careful follow-up.