A total of 93 tumors of the epidermis, its appendages, and dermis were observed in 1,433 (717 males, 716 females) rats employed in oncogenicity studies over a 2-yr period. Mammary gland neoplasms will be reported separately. Fifty-seven (61.3%) were epithelial with 49 in males and 8 in females. Keratoacanthoma was the most frequent epithelial neoplasm in males (22) followed by squamous cell carcinoma (11) and papilloma (5). Sebaceous gland neoplasms seen in males (5) included both adenomas (3) and carcinomas (2). In males, there were also 3 trichoepitheliomas, 1 pilomatricoma, 1 basal cell tumor, and 1 malignant melanoma. Of the 8 epithelial neoplasms in females, there were 3 squamous cell carcinomas, 2 keratoacanthomas, and 1 each basal cell tumor, malignant melanoma, and trichoepithelioma. There were 21 mesenchymal neoplasms in males and 15 in females. The most frequent neoplasm was fibroma (7 males, 8 females) followed by lipoma (7 males, 4 females) and fibrosarcoma (4 males, 3 females). One male had a liposarcoma and 2 males each had hemangioma. The total neoplasm incidence of 70/717 (9.8%) in males and 23/716 (3.2%) in females showed that skin neoplasms were 3 time more common in males than in females. Epithelial neoplasms of the skin were 6 times more common in males than in females. Males were more than twice as likely to have epithelial rather than mesenchymal skin neoplasms whereas the reverse was seen in females.

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Primary malignant neoplasms of the brain and spinal cord occurred in 20/718 male (2.8%) and in 13/717 female (1.8%) Crl:CD®Br strain Sprague-Dawley rats. Of 33 neoplasms, 30 were found in brain while 3 were in the spinal cord. In males and females, the most common brain neoplasm was astrocytoma (13 males, 9 females). Other neoplasms, granular cell tumor (1 male), mixed glioma (2 males, 1 female), reticulosis (1 male, 2 females), and oligodendroglioma (2 males), were especially uncommon. Spinal cord neoplasms included 2 schwannomas (1 male, 1 female) and an astrocytoma (1 male). The overall brain neoplasm incidence was similar for males (2.8%) compared to data compiled for this strain, and there was a 2-fold increase for females (1.8% vs 0.9%) compared to available incidence data.

Abstract. In lifespan studies of 2,242 rats of three strains, 32 neoplasms were identified in brain, meninges and pineal gland. They were astrocytoma ( 16 Wistar, three Sprague-Dawley), ependymoma (four Osborne-Mendel), meningioma (two Osborne-Mendel, one Wistar), pinealoma (two Osborne-Mendel), reticulosis (two Wistar), oligodendroglioma (one Wistar), and gliomatosis (one Wistar).There has been a renaissance of interest in brain tumors of laboratory animals with the realization that exogenous and, perhaps, environmental factors may influence their induction and growth [ I , 81. Spontaneous brain tumors in the rat are infrequently reported [ 1 I], often only as case reports or merely tabulated along with the incidence of other tumors. The largest study with morphologic descriptions involved 41,000 Sprague-Dawley rats with 38 central nervous system tumors for an incidence of only 0.09% [9]. Another study of 7,803 Sprague-Dawley rats described 34 brain or meningeal tumors, an incidence of 0.44% [4]. In other reports, three brain tumors were described in 1,100 Wistar rats [2], and an unusual type of granular cell tumor of the central nervous system was described in 12 aged BN/BI rats [6]. Tabulations of brain tumors in additional reports also indicate a low spontaneous incidence of brain tumors in rats [3, 5 , 10, 12, 14-16]. Our data suggest that the incidence of brain tumors in aged rats is considerably higher than previously reported. Materials and MethodsThree-to 5-month-old healthy female Osborne-Mendel rats were obtained from the Charles River Breeding Colony (Wilmington, Mass.); female Sprague-Dawley and male and female Wistar rats were purchased from Hilltop Laboratory (Chatsworth, Calif.). The rats were in our laboratory for the remainder of their life span in climate-controlled rooms with filtered air kept at 22 k 1" C and 50 f 20% relative humidity. The Osborne-Mendel and Sprague-Dawley rats were housed in pairs in wire-bottom cages placed in automatically flushing racks equipped with automatic waterers. Wistar rats were housed four to five in a 20-centimeter deep plastic cage with 390 cm2 floor space with Sanicel (Paxton Processing, Paxton, Ill.) bedding and water bottles attached to cages. All rats were fed Wayne Lab-Blox (Allied Mills, Chicago, Ill.) laboratory rat diet with 4% crude fat content. The Osborne-Mendel and Sprague-Dawley rats were on a n experiment with cigarette smoke condensate-beeswax pellets implanted into the lung. The Wistar rats were on low-level radiation studies with inhaled or intravenously 318

Primary benign and malignant vascular neoplasms occurred spontaneously in 8 of 710 male (1.1%) and 4 of 710 female (0.6%) CrI:CD®Br strain Sprague-Dawley rats employed in two 2-yr oncogenicity studies (1,400) and as controls in a 1-yr toxicity study (20). Four of 13 neoplasms were found in the spleen; skin and kidney each had 2 neoplasms. Single vascular neoplasms were in the liver, testicle, uterus, mesenteric lymph node, and vagina. Hemangioma was more common (5 males, 2 females) than hemangiosarcoma (3 males, 2 females). Vascular neoplasms were considered the cause of death in 2 females, both with hemangiosarcomas involving the spleen or kidney. One male had 2 primary hemangiomas in separate organs. Vascular neoplasms are infrequently reported [1/82 females (1.2%), 1961; 9/880 both sexes (1.0%), 1985] in this rat strain. The incidence of vascular neoplasms of this report was higher in males (9) than in females (4), in contrast to incidences reported in the literature.