Abstract
Introduction
Clear cell sarcoma of kidney (CCSK) is a rare malignancy accounting for <0.5% of all primary renal tumors, commonly diagnosed between 2 and 4 years of age and rarely occurring in early infancy. The challenging differentiation between CCSK and blastemal Wilms tumor is important because of the distinct clinical pattern of CCSK to recur and metastasize to bone and brain. The aim of this study is to discern subtle features that could assist pathologists in diagnosing CCSK in infancy.
Method
In-depth comparison of clinical, histological, and immunohistochemical findings in a case of CCSK diagnosed at 5 months of age with two cases of CCSK diagnosed at 2 and 3 years of age.
Results
Both groups were male, and each presented with an abdominal mass. Grossly, a single, firm, well-demarcated tumor, morphologically comprising monotonous small primitive round-to-polygonal/spindle cells, was seen in both groups. The major differences between the study groups were growth patterns and stromal reactions. In infancy, the growth pattern was diffusely uniform sheets of malignant cells with no entrapment of tubules and inconspicuous stromal changes. However, in childhood cases, the growth pattern included well-defined tubular entrapment, as well as focal microcyst formation, myxomatous stroma, palisading bodies, and anaplastic and/or rhabdoid histology. In both study groups, the immunohistochemistry showed strong immunoreactivity with cyclin D1 and nonspecific positivity for vimentin, CD99, and BAF47.
Conclusion
CCSK has notoriously diverse histological heterogeneity and mimics other pediatric renal tumors, making diagnosis treacherous, and commonly erroneous as Wilms tumor with unfavorable histology. Despite the advent of immunohistochemical and molecular techniques, a thorough morphologic analysis remains key in accurately diagnosing CCSK at any age, especially in early infancy. This small in-depth comparison of CCSK by age groups suggests that tubular entrapment and stromal changes may be less conspicuous in CCSK in early infancy than at older ages.
Infrequent p53 Gene Mutations and Lack of p53 Protein Expression in Clear Cell Sarcoma of the Kidney: Immunohistochemical Study and Mutation Analysis of p53 in Renal Tumors of Unfavorable Prognosis