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.

Incidence of spontaneous neoplasms in F344 rats throughout the natural life-span

The age-related incidence of spontaneously occurring neoplasms and degenerative diseases in the F344 inbred rat strain was established from the histologic examination of tissues from 160 male and 192 female rats kept throughout their natural life-span. The most common neoplasms were leukemias (25%), mammary tumors (females, 40.6%; males, 23.1%), pituitary adenomas (females, 35.9%; males, 23.8%), and testicular interstitial cell tumors (males, 85%). Various less common neoplasms were observed: thyroid interstitial cell tumors, adrenocortical adenomas, carcinomas of the genitourinary tract, representative central nervous system tumors, pheochromocytomas, and tumors of mesodermal origin including mesotheliomas, myoblastomas, fibromas, and fibrosarcomas. Multiple tumor types were found in 176 of the rats; metastatic tumors were uncommon. Degenerative diseases including myocardial degeneration and nephrosis were often observed. The incidence rate of these neoplasms and degenerative diseases generally increased with advancing age of the animals.

Primary cerebral neoplasia in Rhodesia

In 17 years we have performed 6,505 neurosurgical procedures in the neurosurgical unit of the Salisbury Hospital Group. Only 62% were performed on Africanpatients and 38% on European patients, despite the fact that the African population exceeds the European population by 20 times. This is partly due to the tolerance of rural people towards disease and partly to a number of social factors. The European group has a greater percentage of elderly people than the African group and, although we could not estimate the incidence of tumors among the African group, we would expect their overall incidence per capita to be lower because malignant tumors tend to occur in older people. We do not suspect the existence of a genetic factor in tumor incidence. There were 205 primary intracranial neoplasms in Africans and 244 in Europeans. Histological study shows that 33% of all tumors were meningiomas in the African group compared to 19% in the European group. Gliomas comprised 61.3% of the European series and 48.8% of the African series but the distribution by Kernohan's grading of astrocytomas was the same in both groups. If age was a factor, Grades I and II should have predominated in the African group, but did not. The incidence for each tumor among our European patients followed the patterns reported in various European and USA series. Likewise the pattern emerging from our African series closely paralleled the reports of other workers in Africa. Acoustic neuromas appear to be rather rare among Africans. The average age of all adults with tumors was 15 years lower in the African group than in the European group. However, this is entirely related to the age structure of the population, and not to an earlier age of occurrence. The average ages of medulloblastoma cases were identical. In our European series the occurrence according to age was much the same as that reported by overseas workers. The sex incidence of tumors in the European group seems to be a fair reflection of the situation elsewhere; in the African group it is questionable because men go into the towns to work and leave their families in the country. There was no significant difference in the location of tumors in the two groups. Results of treatment were uniformly inferior in the African group, partly due to the lateness of arrival at the hospital so that the growth was already far advanced and also because many patients suffered poor health from concomitant disease.