Case presentation
A 13-year-old Japanese male was referred to our department for treatment of a right renal tumor that had been detected by abdominal ultrasound in a related pediatric clinic. The patient had been diagnosed with a large right kidney mass at the age of 11 months, and subsequently underwent an open left nephrectomy, resulting in a pathological diagnosis of nephroblastoma. The surgical and pathological findings indicated that the tumor was stage III, and adjuvant chemoradiotherapy was administered, including total abdominal irradiation of 10.5 Gy and DD4A (a multi-drug chemotherapy: vincristine/dactinomycin/doxorubicin). In addition to the nephroblastoma, the patient was also diagnosed with two other urogenital malformations: hypospadias and right cryptorchidism. Following treatment for the nephroblastoma, urethroplasty and right orchiopexy were performed.
Enhanced computed tomography (CT) imaging revealed a 30-mm-sized mass in the right kidney. The imaging pattern indicated chromophobe RCC or translocation RCC in the right kidney. The R.E.N.A.L. nephrometry score, which is a scoring system that categorizes the complexity of kidney tumors, was 8 points (1-3-3-×-1). Bone scintigraphy and positron emission tomography-CT demonstrated an accumulation in the left eighth rib (Figure 1). The clinical diagnosis was right RCC with suspected single bone metastasis. It was hypothesized as being a secondary malignant neoplasm following nephroblastoma treatment. The patient’s serum creatinine level at the time of initial consultation was 0.72 mg/dL. We decided to perform partial nephrectomy by robot-assisted surgery of the renal tumor for preservation of renal function and tumor resection of the left eighth rib. Given the patient’s history of abdominal surgery, the procedure was performed via a retroperitoneal approach. A partial clamp of the renal artery associated with the tumor was performed during resection of the tumor, and the warm ischemic time was 21 minutes. The patient was discharged on postoperative day 8 without any complications. One month post-surgery, the patient’s serum creatinine concentration was 0.80 mg/dL. Pathological examination revealed that the tumor exhibited clear cell RCC characteristics on hematoxylin–eosin staining. However, carbonic anhydrase 9 staining was negative, which is atypical for clear cell RCC. Additional immunohistochemistry revealed positive transcription factor E3 (TFE3) staining, while TFE3 fluorescence in situ hybridization (FISH) revealed a split signal (Figure2). These examinations led to a definitive diagnosis of microphthalmia transcription factor family (MiT-family) translocation RCC, Fuhrman nuclear grade 3, with no sarcomatous change, no lymphovascular invasion, and negative surgical margins. Resection of the left eighth rib was performed 3 months after partial nephrectomy. Histopathological findings demonstrated no evidence of malignancy (fibrotic lesion, lib). The patient is currently undergoing imaging follow-up and has sustained no recurrence for 15 months.