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.