Increased use of regional radiotherapy is associated with improved outcome in a population-based cohort of women with breast cancer with 1-3 positive nodes

Purpose: To examine use of and outcomes from adjuvant locoregional radiotherapy (LRRT) after breast-conserving surgery (BCS) for women with breast cancer with 1-3 positive nodes (1-3N+) before and after the 1997 publication of randomised trial evidence of a survival advantage from post-mastectomy LRRT.

Methods: Data were analysed for 2768 women diagnosed between 1989 and 2005 and referred to the British Columbia Cancer Agency with newly diagnosed pT1-3 breast cancer with 1-3N+, treated with BCS and RT. LRRT use was analysed over time. Ten-year Kaplan-Meier locoregional control (LRC), breast cancer-specific survival (BCSS) and overall survival (OS) curves were compared using the log-rank test. Cox regression modeling of LRC and BCSS were performed.

Results: LRRT use in patients with 1-3N+ increased from 23% before 1997 to 57% after 1997. LRRT was associated with significant improvements in LRC, but not in DRFS, BCSS, or OS. 10--year LRC was 89% with local RT alone and 93% with LRRT (p=0.006). On multivariable analysis, LRRT was associated with improved LRC compared to local RT alone (HR 0.55, 95% CI: 0.40-0.77), but not with significant BCSS differences. Margin status, grade, % positive nodes, and hormonal therapy were significant predictors for LRC, while tumour size, grade, % positive nodes, and hormonal therapy significantly affected BCSS.

Conclusion: Post-BCS LRRT use in British Columbia increased almost threefold in patients with 1-3N+ after 1997. Adjuvant LRRT was associated with improved LRC, but not with improved BCSS compared to breast RT alone.