[Cyclic nucleotides during radiotherapy of breast cancer].

Levels of cAMP and cGMP were higher in breast cancer tissue as compared with benign tumors. Large-fraction irradiation was followed by a decrease in cGMP concentration matched by a rise in cAMP/cGMP ratio in cases of radiosensitive tumors. Small-fraction treatment did not affect cyclic nucleotide levels. Radiotherapy was followed by a decrease in initially raised blood plasma cyclic nucleotide concentration.