Ossifying renal tumor of infancy (ORIT): The clinicopathological and cytogenetic feature of two cases and literature review.

Ossifying renal tumor of infancy (ORTI) is a rare benign pediatric renal tumor, which has typical clinical and pathological features. In this article, the histological features, immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) assay of two cases of ORTI were performed and the literatures were reviewed. Both of the patients presented to hospital with painless gross hematuria without other symptoms. One is 6 months old male, another is 5-month-old. After several diagnostic procedures, they underwent surgery and the histological diagnosis of ORTI was finally made. Grossly, the tumor had a nodular or irregular appearance, often partially calcified and located in the renal pelvis and calyces. The cut surface of this mass was grey-white, solid and firm. Histologically, the tumor was composed of three major histologic components: osteoblast-like cells, spindle cells, and an osteoid core. Immunohistochemistry staining revealed that osteoblast-like cells were positive for EMA, Vimentin and STAB2. Spindle cells were strongly immunoreactive for Vimentin, WT-1 and focally positive for SMA, but were negative for CK, PAX8 and PAX2. The FISH studies with CEP4 probe on interphase nuclei from the two ORTIs, revealed trisomy 4 were 8.97% (case 1) and 12.23% (case 2). Our study showed that clonal trisomy 4 may be considered as a cytogenetic feature of ORTI, which makes it distinct from other pediatric renal tumor.