Incidence of radiation-associated sarcoma after breast-conserving surgery plus radiation.

Abstract

Radiation-associated sarcoma (RAS) is a rare sequela of radiotherapy. Radiotherapy modalities for breast conservation and radiation treatment (BCT) have changed over time. We sought to determine if the incidence of RAS after BCT has changed over time. We identified breast cancer survivors (diagnosed 1988-2012) treated with BCT within the SEER database. We excluded patients with prior cancer, <1-year follow-up/survival, and nonexternal beam radiation (n = 276 301). We identified patients with a subsequent chest sarcoma diagnosis. The primary predictor variable was a 5-year period of breast cancer diagnosis year (1988-1992, 1993-1997, etc.). The incidence of sarcoma was estimated by the Kaplan-Meier method, censoring at sarcoma diagnosis, death, or last follow-up (available through December 2017). Given the known latency of RAS, we used Joinpoint analysis to identify the time point at which RAS incidence significantly increased (start of the analytic window). A log-rank test assessed differences in RAS incidence by diagnosis year. The incidence of RAS was 0.03% at 5 years (95% confidence interval [CI]: 0.03-0.04) and 0.16% at 10 years (95% CI: 0.14-0.18). No statistical difference in RAS incidence by diagnosis year was observed (p = 0.2). RAS remains a rare but persistent sequela after BCT. As new radiation modalities become more common, ongoing surveillance is necessary to track these rare events.