Interstitial lung disorders following postoperative radiotherapy with concurrent or sequential hormonal therapy for breast cancer: a nationwide database study in Japan

Background Hormonal therapy and radiotherapy are conducted concurrently or sequentially after breast cancer surgery. It remains unclear whether concurrent or sequential treatment is safer in terms of lung complications. Using a Japanese nationwide database, this study aimed to compare the occurrence of severe lung complications between concurrent and sequential treatments. Methods We identified patients who underwent partial mastectomy for stage 0-III breast cancer from July 2010 to March 2020 and received adjuvant hormonal therapy and radiotherapy concurrently (n = 1851) or sequentially (n = 18,429). Two propensity score analyses (1:4 matching and overlap weighting) were conducted to compare hospitalization for radiation pneumonitis and pneumonia within 1 year after surgery, and intensive care unit admission and mortality during the hospitalization. We conducted additional analyses stratified by hormonal drugs (aromatase inhibitors and tamoxifen). Results The propensity score-matched analysis showed no significant differences in occurrence of hospitalization for radiation pneumonitis (0.27 vs. 0.58%, p = 0.10) and pneumonia (0.16 vs. 0.58%, p = 0.05) between the concurrent and sequential treatments. The overlap propensity score-weighted analysis also showed no significant differences (0.25 vs. 0.56%, p = 0.08 and 0.15 vs. 0.44%, p = 0.06, respectively). Intensive care unit admission and in-hospital mortality did not differ significantly between the two treatments. The stratified analysis showed similar results. Conclusion Our propensity score analyses revealed no significant differences in severe lung complications between concurrent and sequential hormonal therapy with radiotherapy following breast cancer surgery, regardless of the type of hormonal drugs. Clinicians can provide concurrent or sequential treatment with equivalent attention to early lung complications.