Second tumors after oncologic treatment

Purpose and Approach: To summarize the current knowledge concerning induction of second neoplasms by oncologic treatments, with specific examples, and to address the consequences with regard to the justification of the indication for the therapeutic administration of ionizing radiation according to the radiation protection legislation. To identify open questions and to outline practical consequences for the communication with the patients. Results and Conclusion: Radiotherapy results in a small but significant increase in tumor incidence, i.e., in secondary tumors. This is only relevant, if tumor cure is achieved with the first treatment. Collection of data on second tumors requires lifelong follow-up and/or a consequent documentation in cancer registries. The improvement in survival rates by successful radiotherapy clearly outweighs the reduction of survival by the induction of second tumors. Moreover, latent times for second neoplasms range from years to decades, while the survival after ineffective treatment is substantially shorter. Hence, the administration of ionizing radiation (in the case of clinically proven indications) is justified. Radiotherapy would even be warranted, if the incidence of second tumors were clearly higher than currently estimated, based on the difference in survival times for second tumors versus recurrences.