Rhabdomyocytic nephroblastoma (Wilms' tumor) in the Sprague-Dawley rat

Nephroblastoma in a Sprague Dawley rat unrelated to titanium dioxide nanoparticle exposure in utero

Nephroblastoma is an embryonal tumour that has rarely been reported in laboratory rats. In this case report, a large nephroblastoma with peritoneal seeding was found during necropsy in an 11-month-old, female, Sprague Dawley rat. The rat had a history of indirect exposure to nano-TiO2 (titanium dioxide nanoparticles) during maternal gestation. A firm mass in the upper right abdominal quadrant was palpated. Four weeks later, the animal quickly declined. Nephroblastoma was confirmed by histopathology. Only one rat developed nephroblastoma among the ten littermates. Nephroblastomas in Sprague Dawley rats are typically spontaneous tumours with non-malignant mesenchymal elements. The capability to induce a nephroblastoma with nano-TiO2 is less likely in this case.

Anaplastic nephroblastoma with peritoneal metastasis in an adult female Sprague Dawley rat

Spontaneous nephroblastomas are uncommon tumors of laboratory rats. This report describes a spontaneous nephroblastoma with peritoneal metastasis in an 11-month-old, female Sprague Dawley rat. The rat was part of a breeding program and presented 15 days post parturition with clinical signs including tachypnea, dyspnea and abdominal distension. At necropsy, the right kidney was markedly enlarged by an expansile pale-tan to white multinodular mass with extension into the retroperitoneal space, with multifocal variably sized nodules involving the mesentery, and surface of pancreas, liver, uterus, and ovarian bursa. The rat also had severe bicavitary effusion. Histologically, the renal parenchyma of the affected kidney was replaced by a moderately cellular, poorly-demarcated, non-encapsulated, multilobulated mass that appeared to compress the adjacent renal outer medulla and cortex. Three distinct neoplastic cell populations were identified in this renal tumor: epithelial cells (convoluted and dilated tubules / rare primitive glomeruloid structures), mesenchymal (neoplastic spindle cells in connective tissue), and blastemal cells (primitive neoplastic cells). The extrarenal nodular masses were predominantly composed of neoplastic mesenchymal and pleomorphic blastemal cells. Immunohistochemically, neoplastic epithelial cells in the renal mass were positive for pancytokeratin, and blastemal cells in both renal and extrarenal masses were positive for Wilms’ tumor 1 protein (WT1) and vimentin. Neoplastic mesenchymal elements in both renal and extrarenal masses were positive for vimentin. The neoplasm was negative for chromogranin A and S100. The tumor was classified as an anaplastic nephroblastoma with metastasis to the mesentery and peritoneal organs.

Spontaneous nephroblastoma with striated muscle differentiation in an F344 rat

An eleven-month old male F344/DuCrj (F344) rat was found dead and had right kidney mass at necropsy. Histopathologically, the mass was composed of nests of neoplastic stellate cells. At the center of the nests, neoplastic epithelial cells formed a tubular structure. In the fibrous connective tissue surrounding the nests, neoplastic cells with striations demonstrable by phosphotungstic acid hematoxylin were observed. Immunohistochemically, neoplastic stellate cells were partially positive for Wilms Tumor 1 and vimentin, and neoplastic cells with striations were partially positive for desmin. We diagnosed this tumor as a nephroblastoma with striated muscle differentiation. To our knowledge, this is the first case of nephroblastoma with apparent striated muscle differentiation in an F344 rat.

Proliferative and nonproliferative lesions of the rat and mouse urinary system

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying lesions observed in the urinary tract of rats and mice. The standardized nomenclature of urinary tract lesions presented in this document is also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous developmental and aging lesions as well as those induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for urinary tract lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Intralobar nephroblastematosis: precursor lesions of nephroblastoma in the Sprague-Dawley rat

Precursor lesions of spontaneous nephroblastoma (NB) in rats are here characterized for the first time, with a description of the progression of the tumor in prenatal, postnatal, and adult Sprague-Dawley rats (Upj:TUC[SD]spf.nb), which are genetically predisposed to the tumor. NB in the rat starts as a focal or multifocal interstitial accumulation of intensely basophilic immature (blastema) cells, invariably located in the deep renal cortex. Precursor lesions of NB (designated intralobar nephroblastematosis) and the early tumor do not overtly disrupt the overall structural organization and integrity of the kidney. However, with increasing size and neoplastic transformation, these lesions trap, compress, and displace/replace the existing renal tubules. Nephroblastematous foci occurred in one or both kidneys in tumor-bearing or non-tumor-bearing kidneys and in young and old rats. Like the precursor lesions, the early tumors in rats as young as 6 weeks of age were located in the inner cortex. Well-developed NB was comprised of blastema cells arranged in dense sheets or in ductular structures surrounded by mantles of blastema cells supported by varying amounts of fibromatous stroma. The stroma in one rat was hemangiosarcomatous (triphasic Wilms' tumor). Tumor cells were slightly pleomorphic and had varying amounts of granular cytoplasm with sparse organelles and showed junctional complexes and basal laminae whose frequency apparently depended upon whether the blastema cell tended to differentiate to epithelial or mesenchymal cells. NB in the rat was morphologically similar to immature pre- and postnatal kidneys, regardless of whether it occurred in young or old rats. The deep cortical location and interstitial infiltrative characteristics of precursor lesions of NB in the rat were analogous to intralobar nephrogenic rests, a variant of the precursor to Wilms' tumor in children.