Impact of postmastectomy radiotherapy on the outcomes of breast cancer patients with T1-2 N1 disease: An individual patient data analysis of three clinical trials

PurposeTo assess the impact of postmastectomy radiotherapy (PMRT) on overall survival and relapse-free survival among breast cancer patients with T1-T2 N1 disease who received standard adjuvant systemic therapy.MethodsThis is an individual patient data pooled analysis of 1053 breast cancer patients referred for adjuvant therapy in three clinical trials (BIG02/98, BCIRG001, and BCIRG005). Overall survival was assessed according to whether or not patients received adjuvant radiotherapy through Kaplan-Meier analysis. Univariate and multivariate analyses of predictors of overall and relapse-free survival were conducted through Cox regression analysis.ResultsLocoregional relapse rates (after amedian follow up of 116months) were 5.6% among patients who received adjuvant radiotherapy vs. 6.6% among patients who did not receive adjuvant radiotherapy. Actuarial 5- and 10-year locoregional relapse-free survival rates were 94 and 93%, respectively, among patients who did not receive adjuvant radiotherapy versus 95 and 92% among patients who received adjuvant radiotherapy. The following factors were associated with worse overall survival in multivariate Cox regression analysis: age<40years (P<0.0001), T2 stage (P=0.004), higher lymph node ratio (P<0.0001), and negative hormone receptor status (P<0.0001). Likewise, the following factors were predictive of shorter locoregional relapse-free survival: age40 (P<0.0001), no PMRT (P=0.034), fluorouracil/adriamycin/cyclophosphamide (FAC) chemotherapy (P=0.001), and higher Tstage (P=0.002).ConclusionThe current analysis does not show abeneficial impact of PMRT on overall or relapse-free survival among patients with T1-T2 N1 disease who received standard adjuvant systemic therapy. There is, however, evidence of improvement in locoregional relapse-free survival with PMRT. These findings need to be prospectively validated.