Human cancer natural history, radiation induced immunodepression and post-operative radiation therapy.

For several types of cancers, post-operative radiation therapy is able to reduce the incidence of local recurrences, but has only a relatively small beneficial effect on total survival. Conversely to what has been claimed, this discrepancy is not due to a detrimental effect of radiotherapy. The data do not substantiate the hypothesis that irradiation through an impact on the immune system enhances growth of neoplastic foci outside of the irradiated volume. Several sets of data show that uncontrolled primary tumors or lymph node metastases can be important foci for distant spread. However the analysis of the data shows that post-operative radiotherapy can prevent metastatic spread only in a small subset of patients, those without distant metastases at the initial treatment and in whom local recurrences can be a nidus for distant dissemination before being detected and treated. The results of the clinical trials carried out on patients with breast cancers show that this situation is frequently observed in patients with tumors located in the inner quadrants of the breast who are those in whom the involvement of the internal mammary chain is relatively frequent.