However, when SIRs for potentially radiotherapy-induced vs. nonpotentially radiotherapy-induced sites were compared, significant differences for irradiated vs. nonirradiated women were observed at 10-14 years (1.6 vs. 1.2; P = .03) and 20 or more years (2.6 vs. 0.9; P = .001).
SIRs for various tumor sites were also compared, showing that at 20 or more years after breast cancer diagnosis, irradiated women had a higher SIR ratio for second lung, bronchus, and tracheal malignancies than did the nonirradiated women, at 4.3 vs. 0.7 (P = .0001). Higher SIRs were seen for esophageal and colorectal cancers as well, but the differences did not reach statistical significance.
“There is an increased risk of developing potentially induced cancer, and the risk increases over time since treatment,” Ms. Grantzau said. The ALLEGRO project team will now use a dose-planning system to identify the radiation levels associated with the increased risk.
ALLEGRO is funded under the EURATOM Work Program. Dr. Arriagada and Ms. Grantzau reported no conflicts of interest.