Classification of Neural Tumors in Laboratory Rodents, Emphasizing the Rat

Abstract

Neoplasms of the nervous system, whether spontaneous or induced, are infrequent in laboratory rodents and very rare in other laboratory animal species. The morphology of neural tumors depends on the intrinsic functions and properties of the cell type, the interactions between the neoplasm and surrounding normal tissue, and regressive changes. The incidence of neural neoplasms varies with sex, location, and age of tumor onset. Although the onset of spontaneous tumor development cannot be established in routine oncogenicity studies, calculations using the time of diagnosis (day of death) have revealed significant differences in tumor biology among different rat strains. In the central nervous system, granular cell tumors (a meningioma variant), followed by glial tumors, are the most common neoplasms in rats, whereas glial cell tumors are observed most frequently in mice. Central nervous system tumors usually affect the brain rather than the spinal cord. Other than adrenal gland pheochromocytomas, the most common neoplasms of the peripheral nervous system are schwannomas. Neural tumors may develop in the central nervous system and peripheral nervous system from other cell lineages (including extraneural elements like adipose tissue and lymphocytes), but such lesions are very rare in laboratory animals.

Incidence of Spontaneous Central Nervous System Tumors in CD-1 Mice and Sprague-Dawley, Han-Wistar, and Wistar Rats Used in Carcinogenicity Studies

“…Several reports have identified a comparable sex effect in rats (Solleveld and Boorman 1990;Zwicker et al 1992;Weber et al 2011), but to the authors' knowledge, no such data have been published in mice.…”

Proliferative and Nonproliferative Lesions of the Rat and Mouse Central and Peripheral Nervous Systems

“…Many classification systems have been defined for neuroproliferative lesions in genetically engineered (Weiss et al 2002) and toxicant-treated (Koestner et al 1999;Krinke et al 2000b;Solleveld, Gorgacz, and Koestner 1991;Weber et al 2011) rodents. The current recommendations have been designed to define suitable terms for common proliferative terms in mice and rats.…”

GFAP-Positive Neoplastic Astrocytes in Spontaneous Oligodendrogliomas and Mixed Gliomas of Rats

“…On the other hand, there are no reports describing the existence of GFAP-positive neoplastic astrocytes in rat spontaneous astrocytomas, although detailed immunohistochemical examinations have been done by many researchers (Krinke and Germer 1993;Krinke et al 2000;Nagatani et al 2009;Pruimboom-Brees et al 2004;Solleveld, Gorgacz, and Koestner 1991;Weber et al 2011).…”