Immunologic considerations of large volume radiotherapy.

There is clinical evidence that the immune response can increase or decrease cancer growth. 1) Cancer is increased in congenital immune deficiency states and in those given immuno-suppressants after renal transplantation; 2) there is a correlation between mononuclear cell infiltration and prognosis; 3) spontaneous regression occurs occasionally on an immunologic basis; 4) cancer specific antigens and antibodies can be demonstrated, and 5) immunotherapy can cause tumor regression. The cells that are responsible for the immune response are 1) families of thymic-derived lymphocytes, or T-cells, ("memory," "effector", "helper" or "suppressor" T-cells), and 2) bursal-derived lymphocytes, or B-cells, which on specific sensitization become either plasma cells that produce cytotoxic or blocking antibody or macrophages (A-cells) that process antigen, and may become "armed" with cytophilic antibody. The main effect of local radiotherapy is to destroy certain families of radiosensitive lymphocytes in the afferent, central and efferent components of the immune response. In Hodgkin's disease, extended field radiotherapy causes a prolonged decrease in the number of lymphocytes in the peripheral blood and a decrease in function of the cells, as determined by RNA and DNA synthesis after culture with mitogen, phytohemagglutinin. There is no correlation, however, with the values after treatment and recurrence of the disease. The effect of local radiotherapy to large volumes of tissues, on the incidence of new primary cancers, is uncertain but the majority of reports show that it is no effect.