Neoplasms in dogs receiving low-level gamma radiation during pre- and postnatal development

Beagle dogs were given whole-body exposure to 60Co gamma radiation at one of six ages of pre- or postnatal life. Four-hundred and eighty dogs, 120 for each age at exposure, received 20 R at 8, 28 or 55 days postcoitus (dpc) or at 2 days postpartum (dpp). Similarity 480 dogs, in groups of 120, were exposed to 100 R at these same ages. Exposures of 100 R were also given to 118 dogs at 70 dpp and 231 dogs at 365 dpp. An additional 359 dogs were sham-irradiated. Mean values for each age at exposure ranged from 15.6 to 17.5 rads for 20 R exposures and from 80.8 to 88.3 rads for exposure to 100 R. Mortality due to neoplasia during the initial ten years of the experiment was examined. Twenty dogs died or were killed because of neoplasia, 19 having been irradiated. Tumours in these 19 irradiated dogs included five malignant lymphomas, eight carcinomas (two of mammary origin, two of prostatic origin, and one each of oral mucosa, ovary, urinary bladder, and thyroid origin), four sarcomas (two haemangiosarcomas, one fibrosarcoma and one mast cell sarcoma), one astrocytoma, and one hepatocellular adenoma. Neoplasms occurred in all irradiated groups except 8 dpc (20 and 100 R) and 70 dpp (100 R). Eleven neoplasms developed in dogs irradiated perinatally (55 dpc or 2 dpp) with 20 or 100 R. Four of the tumours in the perinatally irradiated dogs were detected before two years of age. The earliest death was at three months, due to an astrocytoma. Preliminary analyses point to findings of particular interest: (1) the preponderance of neoplasms causing death or euthanasia occurred in irradiated dogs; (2) the unusual finding of four deaths due to neoplasia before two years of age in perinatally irradiated dogs; and (3) the occurrence of five malignant lymphomas in this relatively small irradiated population