Case presentation
A 7-year-old Japanese male presented with a right upper abdominal mass. He had no remarkable past medical history. His parents were non-consanguineous. His father underwent prostatectomy for prostate cancer at age 51. His mother and his elder brother had no remarkable medical history (Fig. 1A ). His general condition was good. Physical examination revealed a large mass in the right upper abdomen. Brown spots were found on the left shoulder, lower back, and lower abdomen. His laboratory tests were normal, except for mildly elevated C-reactive protein (1.30 mg/dL). An enhanced computed tomography (CT) scan showed a large right kidney tumor with multiple cystic lesions that contained enhanced solid components (Fig. 1B ) and a compensatory hypertrophic left kidney. Although he was initially misdiagnosed with multicystic dysplastic kidney (MCDK),18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) revealed uptake on the solid components of the right kidney (Fig. 1C ). Renal scintigraphy showed decreased right kidney function. There was no evidence of distant metastasis by enhanced CT and FDG-PET.
We performed a laparoscopic right nephrectomy. The tumor was inside the kidney with multiple cysts and focal nodules. Pathological examination revealed that cysts were lined by mild eosinophilic simple cuboidal epithelium with mild nuclear atypia and hardly mitotic activity. Tumor cells with relatively prominent nucleoli, surrounded by halos, were located in the limited area (Fig. 1D ). Mild eosinophilic inorganic materials accumulated in a portion of the cysts. Continuous with the cysts, eosinophilic cells showed a papillary growth pattern with a thin vascular core. A nodular area and around the cysts showed a tubular structure and solid thick growth pattern. Multiple lesions were detected inside the kidney, suggesting a tumor of multifocal origin. The resected edge had no tumor cells. All of the hilar lymph node samples were negative for metastases. The Transcription factor E3 split signal was negative in fluorescent in situ hybridization, and the Ki-67 expression was 2%–3%. Immunohistochemical staining was diffusely positive for succinate dehydrogenase B, a cluster of differentiation (CD) 10, epithelial membrane antigen, and paired box 8 and partially positive for pan-cytokeratin (AE1/AE3) and alpha-methylacyl coenzyme A racemase. The staining was negative for cytokeratin 7, carbonic anhydrase 9, CD117, transcription factor EB, and FH (Fig. 1E ). On the basis of these findings, the tumor was pathologically diagnosed with HLRCC-associated RCC. Two years later, abdominal MRI and chest CT showed no postoperative recurrence or metastasis of the tumor, and no appearance of left renal or skin lesions.