Flow cytometry of radiation-induced tumors in rats.

Hundred sixty female Wistar rats were total-body irradiated with 4 Gy gamma rays. Mammary gland tumors started to occur 8 months after irradiation, beside that also tumors of different sites appeared. By flow cytometry (FCM) 30 tumors were examined: mammary gland--22, skin--4, adrenal gland--2, liver--1, thymus--1. Eight tumors were characterized as malignant and 22 as benign. All benign and 6 malignant tumors were composed of diploid cells only. In 2 carcinomas together with diploid cells aneuploid cell lines were also found. DNA index (DI) of aneuploid cells in both carcinomas (1 mammary gland and 1 adrenal gland) indicated values of 1.66 and 1.68, respectively. Most cells of the benign and the malignant tumors occupied G1/0 (79-94%) phase of the cycle. The fraction of S (4.1-14.3%) and G2M (0.5-7.7%) cells was relatively small that suggests a low proliferative activity of radiation-induced tumors.