Reduction by anti-inflammatory corticosteroids of clonogenic growth of allogeneic tumour cells in normal and irradiated tissues of the rat.

Anti-inflammatory corticosteroids administered to rats in high dosages before intravenous injection of allogeneic tumour cells caused 5-10 fold reductions in "take" and clonogenic growth of the cells in lung and kidney and decreased growth and spread of the cells transplanted to leg muscle. Steroid therapy also reduced the effect of local irradiation of lung tissues in increasing tumour colony efficiency (CFE) in the lungs; it also tended to reduce similar effects of sublethal whole body irradiation. A non-steroidal anti-inflammatory drug, phenylbutazone, also reduced CFE in locally irradiated lungs in the rat.The results obtained indicate that corticosteroids do not stimulate the growth of implanted tumour cells by suppressing host immunity but decrease their clonogenic growth by inhibiting local inflammatory reactions to cell arrest, and similarly to local tissue damage caused by x-irradiation; it is asserted that such inflammatory reactions are growth promoting and thereby stimulate regeneration of stroma (repair) and also support survival and early growth of the tumour cell.