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

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.

The abnormal karyotype t(10;17)(q22;p13) has been reported previously in CCSK 7], and CpG sites in the THBS1 gene were shown to be specifically hypermethylated in CCSK 8]. A new chromosomal abnormality was detected in our patient, 46,XY,der(3)(3pter???3q23::7?::3?::7p13???7pter)der(7)(X?::7p11.2???7q22::3?::Xq13???Xqter)der(X)del(X)(p11.2p22.1)t(X;7)(q11;?).
A complex karyotype, containing chromosomal 3, chromosomal 7, and X chromosomal abnormalities,
was detected with spectral karyotyping FISH, in which a fragment of chromosome 7 was
added to the partially deleted X chromosome. It is unclear whether this abnormality
was involved in the development of CCSK, although renal cell sarcoma (RCC) with an
Xp11.2 translocation has been reported 9]–11]. Calcification and CCSK occurrence, which were two features of our patient, in an
older child or young adult are characteristics of RCC with the Xp11.2 translocation
9]–11]. Interestingly, both patients with Xp11.2 RCC and our patient display X-chromosome
abnormalities. Therefore, it is likely that an X-chromosome aberration produces an
atypical pathogenesis in CCSK, including calcification and huge areas of necrosis.

CCSK is considered an unfavorable histological renal tumor by the National Wilms Tumor
Study Group (NWTSG) and JWiTS 1], 2], 12]–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.