Combination therapy of malignant tumors with ionizing radiations and chemicals; a review.

Since the discovery of the damaging effects of ionizing radiations on cells, attempts have been made to increase the radiation curability of malig nant neoplasms by the simultaneous administra tion of various chemical agents. Three major ave nues of approach will be reviewed : (a) combining radiation with agents which themselves have antitumor properties in an attempt to gain a synergistic action; (6) sensitizing the tumor to radiation by means of a noncarcinostatic agent; (c) intro ducing into the tumor a compound which will in crease the radiation dose to the tumor by second ary radiation or by nuclear disintegration. A re view of previous experience in these fields is needed because of the discovery of better chemotherapeutic agents, the increasing knowledge of funda mental radiobiology, and the advent of biologically applicable beams of electrons, neutrons, and heavy particles. The literature is extensive, and it is impossible to include reference to all work that has been done, but an effort has been made to include all the major trends of experimentation. The authors have exercised critical discretion as to the material which is included. Whenever possible, examples of investigations with human tumors, animal tu mors, and in vitro technics have been cited. Reference has been omitted to agents which have a systemic effect, such as the sex hormones (16) and cortisone (15) which may alter tumors by indirect pathways, and to radioactive isotopes such as P32, I131,and Au198which are of proved value (5).