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Effects of Radiation Type and Dose and the Role of Glucocorticoids, Gonadectomy, and Thyroidectomy in Mammary Tumor Induction in Mammotropin-secreting Pituitary Tumor-grafted Rats¹

Department of Human Oncology [K. H. C., J. J. C.], Wisconsin Clinical Cancer Center, and Department of Radiology [K. H. C.] and Statistics [J. J. C.], University of Wisconsin Medical School, Madison, Wisconsin 53706

Three experiments on the Induction of mammary neoplasms by total 11- to 100-rad neutron or 50- to 500-rad -radiation of female Fischer or W/Fu rats are reported. Grafts of mammotropin-secreting pituitary tumor were used to elevate mammotropic hormone levels. The results (a) confirm and extend previous reports that neutrons are more efficient in carcinoma induction than are -rays (the neutron relative biological effectiveness for first carcinomas was 3.68) and (b) demonstrate that the potentiation of carcinoma induction by adrenalectomy is reversed by glucocorticoid replacement. Statistical analysis of the data by procedures that take into account time at risk as well as tumor frequency indicates that multiple mammary tumora do not occur independently (i.e., a first mammary neoplasm significantly increases the probability of development of another neoplasm). The statistical procedure used in this analysis is presented.

¹ Supported in part by Research Grant 5 R01 CA13881-04 and Program Project Grant 5 P01 CA19276-01 awarded by the National Cancer Institute. Department of Health, Education and Welfare. Salary support in part from Cancer Center Grant 5 P30 CA14520-05 awarded to the Wisconsin Clinical Cancer Center from the National Cancer Institute.

² To whom requests for reprints should be addressed, at Radiobiology Laboratorires, K4/312, WCCC, 600 Highland Avenue, Madison, Wis. 53706.

Received 10/25/77. Accepted 3/ 1/78.