A case of spontaneous nephroblastoma characterized by two distinct morphologies in a Slc:CD(SD)IGS rat

We report a spontaneous case of nephroblastoma in a 26-week-old female Slc:CD(SD) rat. Macroscopically, there was a yellow mass in the left kidney that included another small yellowish-white mass. Histologically, the mass was located mainly in the cortex of the kidney. The tumor showed two distinct morphologies corresponding to the macroscopic findings: a blastemal cell dominant area (blastemal area) with primitive glomeruli and immature tubules and a columnar epithelial tubule dominant area with blastemal cell cuffing on (epithelial area). The epithelial area was located inside the blastemal area and the two morphologies were characterized by the lack of a transition region. Nephroblastoma is known to be biphasic or triphasic and showing transitional features. To our knowledge, there is no report of such nephroblastoma comprising two histologically distinct areas without transition. Therefore, the two distinct morphologies of this case with no transitional characteristic is a rare feature in nephroblastoma.