Risk of developing subsequent primary lung cancer after receiving radiation for breast cancer.

Background: Radiotherapy (RT) is integral to breast cancer treatment, especially in the current era that emphasizes breast conservation. The aim of our study was to determine the incidence of subsequent primary lung cancer after RT exposure for breast cancer over a time span of 3 decades to quantify this risk over time as modern oncologic treatment continues to evolve.

Methods: The SEER (Surveillance, Epidemiology, and End Results) database was queried from 1988 to 2014 for patients diagnosed with nonmetastatic breast cancer. Patients who subsequently developed primary lung cancer were identified. Multivariable regression modeling was performed to identify independent factors associated with the development of lung cancer stratified by follow up intervals of 5 to 9 years, 10 to 15 years, and >15 years after breast cancer diagnosis.

Results: Of the 612,746 patients who met our inclusion criteria, 319,014 (52%) were irradiated. primary lung cancer developed in 5556 patients (1.74%) in the RT group versus 4935 patients (1.68%) in the non-RT group. In a multivariable model stratified by follow-up duration, the overall HR of developing subsequent ipsilateral lung cancer in the RT group was 1.14 ( = .036) after 5 to 9 years of follow-up, 1.28 ( = .002) after 10 to 15 years of follow-up, and 1.30 ( = .014) after >15 years of follow-up. The HR of contralateral lung cancer was not increased at any time interval.

Conclusions: The increased risk of developing a primary lung cancer secondary to RT exposure for breast cancer is much lower than previously published. Modern RT techniques may have contributed to the improved risk profile, and this updated study is important for counseling and surveillance of breast cancer patients.