Early onset of tumors in mice that were exposed continuously to low-dose-rate gamma-rays

We previously reported that life shortening induced by continuous gamma-ray irradiation at a low-dose rate in B6C3F1 mice appeared to be caused by death from the early onset of malignant lymphomas. Life-shortening and tumor development of SPF C3H-He Nrs mice irradiated with 137Cs-gamma-ray at dose rate of 20 mGy/22 hr/day for about 400 days (total accumulated dose: 8 Gy) were examined to verify the strain differences and tumor types. Respective lifespans were significantly shortened by 137 and 41 days in irradiated female and male C3H/He Nrs mice, compared to non-irradiated mice. Significant life-shortening was observed in mice that died of malignant lymphomas, mammary tumors, ovarian tumors, liver tumors, acute myeloid leukemias (only in female), and soft-tissue tumors (only in female). These results suggest that life shortening caused by early onset of malignant lymphomas and other various tumors occur in irradiated C3H mice as well as B6C3F1 mice. (author)