[SMALL RENAL CELL CARCINOMA METASTASIS TO THE IPSILATERAL PERIRENAL FAT SYNCHRONOUSLY: A CASE REPORT]

Small renal cell carcinoma with metastases is rare; thus, to the best of our knowledge, this is the first case of synchronous metastasis to the ipsilateral perirenal fat.A 70-year-old man visited our hospital because of early gastric carcinoma. Contrast-enhanced computed tomography revealed a right renal tumor and two small nodules in the ipsilateral perirenal fat. The renal tumor was 3 cm in diameter and consistent with clear cell renal cell carcinoma. The enhancement pattern of the nodules was similar to that of the renal tumor, we diagnosed cT1aN0M1. Transperitoneal laparoscopic radical nephrectomy of the right kidney was performed. Postoperative pathological analysis showed clear cell renal cell carcinoma of the right kidney, pT1a, G2>1, INFa, v0, ly0, and two nodules in ipsilateral perirenal fat had comparable pathological findings. At 11th month of postoperative follow-up, CT revealed multiple nodules in the left pleura. Pembrolizumab plus axitinib was administered every 3 weeks. Multiple pleural metastases disappeared 3 months after the therapy; however, grade 2 (CTCAE v5.0) diarrhea and hoarseness emerged. Owing to the persistence of symptoms despite axitinib cessation, pembrolizumab was also discontinued. After 2 months of withdrawal, the patient's symptoms resolved spontaneously. After consultation with the patient, he was followed up with no further treatment. He is alive with no evidence of recurrence 36 months after surgery.