Clear cell sarcoma of the kidney with calcification and a novel chromosomal abnormality: a case report

A 9-year-old male presented with a renal tumor that showed a cystic structure with calcification on computed tomography. A pathological analysis of the resected tumor suggested clear cell sarcoma of the kidney (CCSK). Thus, this patient suffered atypical CCSK with significant calcification and gross necrosis. A novel chromosomal abnormality was also identified in the tumor.


Background
Clear cell sarcoma of the kidney (CCSK) is a rare renal tumor in children, second to Wilms tumor. CCSK represents 2-9 % of all pediatric renal tumors and generally arises before the age of 5 years [1,2]. The male-tofemale ratio is almost 2:1 [1,2]. Its typical features are a mucoid texture, necrotic foci, and prominent cyst formation. Multiple histological patterns (classic, myxoid, sclerosing, cellular, epithelioid, palisading, spindle, storiform, and anaplastic) are blended together [1]. A CCSK in a 9-year-old male is described with an atypical pathological status, including gross necrosis and calcification.

Case presentation
A 9-year-old boy complained of abdominal bloating. Blood parameters, including neuron specific enolase, alpha fetoprotein, and beta human chorionic gonadotropin, were in the normal ranges, and his urinary vanillylmandelic acid and homovanillic acid were not elevated. Unenhanced abdominal computed tomography (CT) revealed a tumor with calcification in the left kidney, with infiltration of the renal sinus and 15 cm wide (Fig. 1a). Contrast-enhanced CT revealed a heterogeneously enhancing mass completely enclosed by the renal capsule (Fig. 1b). No metastasis was detected in the lungs, liver, or bone by analysis of CT, magnetic resonance imaging and 99m Tc scintigraphy. After complete surgical resection, the tumor showed heterogeneous pathological tissues divided by septa and included necrotic tissue (Fig. 2). Calcification was found around the necrotic tissue, but no macroscopic osteoplasty was observed. Pathological analysis suggested a monomorphic malignant neoplasm composed of plump or spindleshaped cells with elongated, vesicular nuclei or small nuclei and variable amounts of clear cytoplasm (Fig. 3). These results prompted a diagnosis of stage 2 clear cell sarcoma of the kidney (CCSK).
Chemotherapy was administered according to the Japanese Wilms Tumor Study (JWiTS)-2 Regimen I, including vincristine, doxorubicin, and cyclophosphamide. The patient has remained in complete remission for 3 years.

Discussion
In terms of its pathological features, CCSK is most commonly described as a tan-grey, soft, and mucoid mass on cut section [1,2]. Cystic foci are nearly universal and occasionally constitute the dominant feature, prompting radiological and gross pathological diagnoses of multilocular renal cyst [1,2]. The microscopic appearance of these lesions also mimics cystic nephroma. Within these typically large and relatively homogeneous tumors, discrete foci of necrosis and hemorrhage are common on microscopic analysis [1,2]. On the contrary, the tumor in our patient appeared as a huge heterogeneous cystic mass on enhanced CT. Gross and microscopic pathological analysis showed that the cysts contained necrotic tissues. These findings are not typical of CCSK.
Radiographically demonstrable calcification is observed in 3-17 % of primary Wilms tumors [3,4], but calcification is rarely reported in CCSK. Glass et al. reported calcification in CCSK, which was detected as acoustic shadowing on sonography, indicating a calcific deposit [5]. In the present case, calcification was detected on CT. The pathological findings revealed that the calcification was present around the sphacelus, which is considered dystrophic calcification attributable to necrosis [6]. These results suggest that huge areas of necrosis and calcification are not reasons to reject a diagnosis of CCSK.
CCSK is considered an unfavorable histological renal tumor by the National Wilms Tumor Study Group (NWTSG) and JWiTS [1,2,[12][13][14]. The survival rate for stage 2 CCSK is reported to be 75 % when doxorubicin is added to the therapeutic regimen [1,2,13,14]. However, necrosis is reported to increase the risk of tumor-related mortality in CCSK [13]. Our patient requires careful follow-up.

Conclusion
The calcification is not a reason to reject a diagnosis of CCSK.

Consent
Written informed consent was obtained from the parents of the patient for publication of this Case Report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.