Spontaneous tumors in ACI/N rats.

One hundred ninety-five spontaneous tumors, developing in 55 male and 209 female ACI/N rats in 169 weeks, were studied. The incidence was 56% (31/55) in males and 52% (108/209) in females; their average survival time was 113 and 108 weeks, respectively. These neoplasms were found in all organ systems except those of the sensory and locomotor systems. In the males, interstitial cell tumors of the testis (45.5%, 25/55) were most frequent, followed by those in the adrenal (16.4%, 9/55) and pituitary glands (5.5%, 3/55), skin (5.5%, 3/55), and urinary bladder (3.6%, 2/55). In female rats, tumors of the pituitary gland (21.1%, 44/209), uterus (12.9%, 27/209), mammary gland (11.1%, 23/209), adrenal gland (5.7%, 12/209), urinary bladder (4.8%, 10/209), thymus and lymph nodes (4.3%, 9/209), subcutaneous tissues (1.4%, 3/209), heart (1.4%, 3/209), vagina (1.0%, 2/209), and salivary gland (1.0%, 2/209) were detected. In addition, tumors of the glandular stomach, small intestine, spleen, trachea, lacrymal gland, ovary, brain, kidney, thyroid, and bone marrow were detected in 1 female each, and those of the small intestine, spleen, lung, and peritoneum in 1 male rat each. Only 6 adenocarcinomas of the uterus, 3 lymphatic leukemias, 1 cortical carcinoma, and 1 mesothelioma of 195 tumors observed in the present studies metastasized to remote organs.