Mastectomy alone for pT1-2 pN0-1 breast cancer patients: when postmastectomy radiotherapy is indicated

Purpose: To assess outcome of breast cancer (BC) stages pT1-2 N0-1 after mastectomy alone and to identify prognostic factors calling for the need of postmastectomy radiotherapy. Methods: Patients who were not eligible for breast conserving surgery (BCS) were operated on with mastectomy between 1998 and 2008. Locoregional (LRR), distant (DM) control and breast cancer specific survival (BCSS) were retrospectively evaluated. Cumulative incidence (CI) of events was estimated according to Kalbfleisch and Prentice while Gray’s test tested difference. Kaplan–Meier method for survival and Cox proportional hazards model for univariable and multivariable analysis were used. A matched pair analysis between mastectomy alone and BCS plus whole breast irradiation (WBI), using the propensity score method, was performed. Results: 1281 pT1-2 N0 and 1081 pT1-2 N1 were identified. Median follow-up was 8.2 years (9.2 years for survival). Overall, LRR rate was low for both N0 and N1 subgroups (10-year CI, 8.8% and 10.9%, respectively). Young age, lymphovascular invasion and Ki-67 ≥ 20% were proved to be statistically significant prognostic factors at multivariable analysis. The combination of ≥ 2 risk factors increased LRR rate to ≥ 15%. Risk factors combination weighed on LRR rate more than nodal status itself. DM rate doubled moving from negative to positive nodal status (10-year CI 10.5% versus 20.3%, respectively). BCSS remained high in both N0 and N1 subgroups (10-year CI 92.4% versus 84.5%, respectively). Remarkably, all the molecular subtypes except Luminal A significantly affected DM and BCSS both in the N0 and N1 subgroups. Nodes number significantly impacted on DM and BCSS but not on locoregional control. In the matched pair analysis, WBI decreased nodal recurrence rate and improved distant control, without affecting survival. Conclusions: Selected patients, namely those with at least two additional risk factors, presented high enough LRR risk to support the use of postmastectomy radiotherapy in both N0 and N1 subgroups. Moreover, the observation that radiotherapy may provide benefits that go beyond local control deserves to be further investigated.