The effects of fractionated gamma irradiation on induction of mammary carcinoma in normal and estrogen-treated rats.

The effects of dose fractionation on induction of mammary carcinoma were studied in normal and estrogen-treated female rats of the inbred WAG/Rij strain. Groups of 40 animals received total-body doses of 1 or 2 Gy of (137)Cs gamma radiation, administered in fractions of 2.5, 10 or 40 mGy with intervals of 12 h, or in fractions of 10 mGy with intervals of 2, 5 or 24 h. The irradiations were started at the age of 8 weeks. Estrogen treatment was accomplished by implantation of a pellet containing estrogen at the age of 6 weeks. All mammary tumors were resected and classified histologically as carcinoma or fibroadenoma. The age-specific incidence of mammary carcinoma was compared with that in control groups of unirradiated normal or estrogen-treated rats and was expressed as excess normalized risk, using lifetime statistical analysis with both parametric and nonparametric methods. The data were also compared to the results of single-dose experiments reported in previous papers. Fractionated irradiation increased the risk of mammary cancer in both normal and estrogen-treated rats compared to the corresponding unirradiated control group. The excess normalized risk per unit of total dose was approximately equal with or without estrogen treatment. Without estrogen treatment, the effects of the single-dose and fractionated irradiations were approximately equal. In estrogen-treated animals, however, single-dose irradiation was up to 15 times more carcinogenic than the fractionated exposures. This fractionation effect appeared to vanish for total doses below approximately 0.3 Gy. With estrogen treatment, the excess normalized risk was significantly higher for dose fractions of 40 mGy than for fractions of 10 mGy. The risk was also markedly higher for fractionation intervals of 2 or 5 h than for intervals of 12 or 24 h. The results of these experiments show that the effects of dose fractionation on the induction of mammary carcinoma may depend on hormonal status, the total dose delivered, the dose per fraction, and the fractionation interval.

The carcinogenic risk of high dose total body irradiation in non-human primates.

PURPOSE: High dose total body irradiation (TBI) in combination with chemotherapy, followed by rescue with bone marrow transplantation (BMT), is increasingly used for the treatment of haematological malignancies. With the increasing success of this treatment and its current introduction for treating refractory autoimmune diseases the risk of radiation carcinogenesis is of growing concern. Studies on tumour induction in non-human primates are of relevance in this context since the response of this species to radiation does not differ much from that in man. MATERIALS AND METHODS: Since the early sixties, studies have been performed on acute effects in Rhesus monkeys and the protective action of bone marrow transplantation after irradiation with X-rays (average total body dose 6.8 Gy) and fission neutrons (average dose 3.4 Gy). Of those monkeys, which were irradiated and reconstituted with autologous bone marrow, 20 animals in the X-irradiated group and nine animals in the neutron group survived more than 3 years. A group of 21 non-irradiated Rhesus monkeys of a comparable age distribution served as controls. All animals were regularly screened for the occurrence of neoplasms. Complete necropsies were performed after natural death or euthanasia. RESULTS: At post-irradiation intervals of 4-21 years an appreciable number of tumours was observed. In the neutron irradiated group eight out of nine animals died with one or more malignant tumours. In the X-irradiated group this fraction was 10 out of 20. The tumours in the control group, in seven out of the 21 animals, appeared at much older age compared with those in the irradiated cohorts. The histogenesis of the tumours was diverse with a preponderance of renal carcinoma, sarcomas among which osteosarcomas, and malignant glomus tumours in the irradiated groups. CONCLUSIONS: When corrected for competing risks, the carcinogenic risk of TBI in the Rhesus monkeys is similar to that derived from the studies of the Japanese atomic bomb survivors. The increase of the risk by a factor of 8, observed in the monkeys, indicates that patients are likely to develop malignancies more frequently and much earlier in life after TBI than non-exposed individuals. This finding underlines the necessity of regular screening of long-term surviving patients subjected to TBI and BMT.

Induction of mammary tumors in rats by single-dose gamma irradiation at different ages.

The effect of age at exposure on induction of mammary tumors was studied in female rats of the inbred WAG/Rij strain. Groups of 40 animals were exposed to a single total-body dose of 1 or 2 Gy of 137Cs gamma radiation at ages of 8, 12, 16, 22, 36 or 64 weeks and were observed for life. Mammary tumors, identified as nodules persisting and growing for 6 weeks, were resected and classified histologically as carcinoma or fibroadenoma. The age-specific incidence of mammary carcinoma was compared with that in a group of 120 unirradiated control rats, using lifetime statistical analysis with both parametric and nonparametric methods. The excess normalized risk of carcinoma was 0.9 for 1 Gy and 2.2 for 2 Gy in age groups 8-36 weeks, with no significant differences between the age groups. However, irradiation at 64 weeks yielded fewer carcinomas than in the controls, the excess normalized risk being -0.7 and -0.3 for 1 and 2 Gy, respectively. The occurrence of one or more fibroadenomas did not influence the incidence of carcinoma. The present data agree closely with the results reported previously for rats irradiated at age 8 or 17 weeks with a dose of 1.2 Gy. The reduced risk of radiation exposure at midlife is consistent with the available epidemiological data for exposed women. Although our findings have been obtained with a single total-body dose that is several orders of magnitude higher than the multiple doses delivered to the mammary gland during mammography, it is suggested that radiological screening for mammary cancer after the age of menopause will not increase the normal incidence of breast cancer.

The influence of estrogen treatment on induction of mammary carcinoma in rats by single-dose gamma irradiation at different ages.

The effect of age at exposure on induction of mammary carcinoma was studied in female rats of the inbred WAG/Rij strain that were treated with estrogen. Groups of 40 animals were exposed to a single total-body dose of 1 or 2 Gy of 137Cs gamma radiation at age 8, 10, 12, 15, 22, 36 or 64 weeks. Hormone levels in the animals were increased by implantation of a pellet containing Estradiol-17beta 2 weeks prior to irradiation. Animals were killed when moribund. All mammary tumors were resected and classified histologically as carcinoma or fibroadenoma. The age-specific incidence of mammary carcinoma was compared with that in control groups of unirradiated estrogen-treated rats using lifetime statistical analysis with both parametric and nonparametric methods. The excess normalized risk of carcinoma was 7.7 for both 1 and 2 Gy in the age groups 8-15 weeks, with no significant differences between the age groups. However, in the age groups 22-64 weeks, the excess normalized risk decreased with increasing age at exposure. Irradiation at 64 weeks yielded fewer carcinomas than in the controls, with an excess normalized risk of -0.6 for both 1 and 2 Gy. The excess normalized risk was 10-80 in estrogen-treated controls compared to untreated rats. The present data agree with the results reported previously for estrogen-treated rats irradiated at ages 8 or 17 weeks with doses of 0.3 or 1.2 Gy. The reduced risk of radiation exposure at midlife observed in this study in hormone-treated rats has also been reported for animals not treated with estrogens. The present findings support the earlier conclusion that radiological screening for mammary cancer after the age of menopause will not increase the normal incidence of breast cancer. Estrogen treatment at midlife may increase the risk of breast cancer in women using replacement estrogens during and after menopause.

Intercomparison of measurement techniques used in radon exposure facilities for animals in Europe.

The biological effects of exposure to radon and its progeny are being studied in animals by three laboratories in Europe. The facilities used for such exposures are described, together with the methods used to estimate radon progeny concentrations and the activity deposited in the lungs of exposed animals. As the facilities and methods vary, a series of comparison exercises has been carried out at the three facilities; CEA/COGEMA, Razes, France, TNO, Rijswijk, The Netherlands and AEA Technology, Harwell, U.K. The results of the exercise are presented together with reasons for the discrepancies in results between the groups thus ensuring that estimates of exposure provided by the groups for their studies is directly comparable.

Flow cytometric analysis of peripheral blood erythrocyte chimerism in alpha-thalassemic mice.

A rapid and reliable method for longitudinal studies on the degree of red cell chimerism following bone marrow transplantation of alpha-thalassemic recipient mice is presented. Blood obtained by tail clipping from transplanted mice was analyzed by measuring forward light scatter (FLS) distribution of red cells using a flow cytometer. Amplification and threshold of FLS were specifically adjusted. For flow cytometric analysis, the red cells needed to be suspended in hypotonic saline (103 mmol/l NaCl). Osmotic fragility testing showed that lysis of erythrocytes did not significantly influence the measurements. Flow cytometric measurement allowed for a rapid determination of the degree of red cell chimerism.