Purpose: To characterize second tumors that developed in or near the high-dose areas of a previous radiotherapy, regarding their frequency, entities, latency, and dose dependence.
Patients and methods: 9,995/15,449 tumor patients of the Radiation Oncology Department in Ulm, Germany, treated between 1981 and 2003, survived at least 1 year after radiotherapy. By long-term follow-up and review of treatment documentation, 100 of them were identified who developed an independent second cancer in or near the irradiated first tumor site.
Results: Major primary malignancies were breast cancer (27%), lymphoma (24%), and pelvic gynecologic tumors (17%). Main second tumors were carcinomas of the upper (18%) and lower (12%) gastrointestinal tract, head and neck tumors (10%), lymphoma (10%), breast cancer (9%), sarcoma (9%), and lung cancer (8%). Overall median second tumor latency was 7.4 years (1-42 years). For colorectal cancer it was 3.5 and for leukemia 4.3 years, but for sarcoma 11.7 and for breast cancer 17.1 years. The relatively frequent second tumors of the upper gastrointestinal tract were associated with median radiation doses of 24 Gy. By contrast, second colorectal cancer and sarcoma developed after median doses of 50 Gy.
Conclusion: The 5- and 15-year probability to develop a histopathologically independent second tumor in or near the irradiated first tumor site, i.e., after intermediate or high radiation doses, was 0.5% and 2.2%, respectively. To identify potentially radiogenic second malignancies, a follow-up far beyond 5 years is mandatory. The incidence and potential dose-response relationship intermediate will be analyzed by a case-case and a case-control study of the Ulm data.