Mammary carcinoma cell population growth in preirradiated and unirradiated transplant sites. Viable tumor growth, vascularity, and the tumor-bed effect.

Although preirradiation of the transplant site profoundly depresses growth of subsequently grafted carcinomas, the potential rate of tumor cell population growth was very similar within the viable regions of large and small tumors grafted in preirradiated or unirradiated sites. The vascular space per unit of viable tumor mass has previously been shown to be constant in such viable tumor tissue. It is concluded that the tumor-bed effect is due to suppression of vascular growth capability. Insofar as therapeutic procedures depend on relative functional vascular space, the sensitivity per unit mass of viable tissue would be expected to be very similar in large and small tumors growing in unirradiated or preirradiated sites.