Effects of Roentgen Irradiation on the Tumor Bed: III. The Different Inhibiting Action on the Growth of Mouse Mammary Carcinoma Resulting from Pre- or Posttransplantation Irradiation

Abstract

The effects of pre- and posttransplantation roentgen irradiation at different time intervals on mammary cancer in Z (C3H) mice were studied. The average survival of the animals and the incidence, latent period, and growth rate of the tumor transplants were determined. The tumors were very radioresistant when irradiated more than 3 weeks after the transplantation. By contrast, tumor growth could be completely suppressed or greatly delayed if the tumor area was irradiated within 2 weeks after the transplantation. The latent period, during which the tumor cells lay dormant, lasted for many months or even exceeded one year if the irradiation was given a short time after the transplantation. Pretransplantation irradiation of the tumor bed did not prevent tumor growth completely but did retard tumor development and prolonged the average survival of the animals. Tumor cells transferred by serial transplantation over many generations appeared more resistant to immediate posttransplantation irradiation than tumor cells transferred only a few times. Data were interpreted in terms of (1) the influence of the recipient host on the radiosensitivity of transplanted tumors, (2) a possible difference in the radiosensitivity of the tumor cells at different time intervals after the transplantation, or (3) a result of better oxygenation of the tumor cells within the first couple of weeks after the transplantation.