Spontaneous glioblastoma multiforme in a Charles River CD rat.

The purpose of this report is to describe the occurrence and pathology of a spontaneous and rare brain tumor in a strain of rat commonly employed for drug and chemical safety testing. Glioblastoma multiforme is another term for “malignant astrocytoma” (Grade 3 or 4) and is characterized by cellular and nuclear hyperchromasia and pleomorphism, multinucleated giant cells and pallisading necrosis. The tumor exhibits highly aggressive invasive behavior. In contrast, “anaplastic glioma” is a term applied to any malignant tumor of glial cells including those containing astrocytes. Often, there are variable mixtures of cell types within a given tumor. None of these anaplastic gliomas exhibit the degree of anaplasia or invasive behavior seen in the tumor of this report. Primary brain tumors in rats are infrequent compared to tumors found in other organ systems. In a recent report, astrocytoma was the most frequent glial cell tumor in Sprague-Dawley rats with an incidence of 28/2,630 in males and 18/2,765 in females (3). This literature report included a total of 88 brain tumors from 5,395 untreated controls and 297 brain tumors from a total of 19,251 rats examined in the combined control and treated groups. None of the astrocytomas reported satisfied the criteria needed for designation as glioblastoma multiforme. A 1974 report of 38 naturally occurring brain tumors found in 4 1,000 Sprague-Dawley rats over a 5-year period included 10 astrocytomas or