Estimation of Annual Secondary Lung Cancer Deaths Using Various Adjuvant Breast Radiotherapy Techniques for Early-Stage Cancers

Purpose: Secondary lung cancer (SLC) can offset the benefit of adjuvant breast radiotherapy (RT), and risks compound sharply after 25 to 30 years. We hypothesized that SLC risk is mainly an issue for early-stage breast cancer, and that lives could be saved using different RT techniques. Patients and Methods: The SEER database was used to extract breast patient age, stage survival, and radiotherapy utilization over time and per stage and to assess the factors associated with increased SLC risk with a multivariable competing risk Cox model. The number of SLC was calculated using the BEIR model modified with patient survival, age, and use of RT from the SEER database. Stage distribution and number of new breast cancer cases were obtained from the NAACCR. Mean lung dose for various irradiation techniques was obtained from measurement or literature. Results: Out of the 765,697 non-metastatic breast cancers in the SEER database from 1988 to 2012, 49.8% received RT. RT significantly increased the SLC risk for longer follow-up (HR=1.58), early stage including DCIS, stage I and IIA (HR = 1.11), and younger age (HR=1.061) (all p