Breast conserving therapy versus mastectomy in T1-2N2 stage breast cancer: a population based study on 10-year overall, relative and distant metastasis-free survival in 3,071 patients

Background: Recent observational studies showed improved survival after breast conserving therapy (surgery with radiation therapy, BCT) compared to mastectomy (MAST) in T1−2N0−2 stage breast cancer. However, N2 stage is described to affect patients’ prognosis dramatically compared to N0−1 stage, and is according to the Dutch guidelines an indication for postmastectomy radiation therapy (RT). We aimed to determine 10-year overall survival (OS), relative survival (RS) and distant metastasis-free survival (DMFS) in T1−2N2 breast cancer after BCT or MAST with RT, stratified for T stage. Material and Methods: All women diagnosed with primary invasive T1−2N2 breast cancer between 1 January 2000 and 31 December 2004, treated with either BCT or MAST with RT, were selected from the Netherlands Cancer Registry. Multivariable Cox regression was performed to estimate 10-year OS, overall and stratified for T stage. Ten-year RS was estimated using general linear models with Poisson distribution, with life tables of the general population. Ten-year DMFS was determined on the 2003 cohort, of which an active follow-up was conducted registering all recurrent events. Multiple imputation was performed to account for missing Results: The total population included 3,071 patients, of which 1,055 (34.4%) received BCT and 2,016 (65.7%) received MAST with RT. No difference in 10-year OS and RS between the treatments was observed in T1N2 stage. However, in T2N2 stage, BCT was significantly associated with improved 10-year OS and RS compared to MAST with RT (HRadjusted 0.82 (95% CI: 0.71–0.96) and 0.81 (95% CI: 0.67–0.97), respectively). The 2003 cohort, consisting of 594 patients, presented with similar characteristics as the full cohort. No significant difference between BCT and MAST with RT was found for 10-year DMFS in T1N2 and T2N2 stage (HRadjusted 1.15 (95% CI: 0.69–1.93) and 0.75 (95% CI: 0.51–1.11), respectively) (Table). Table: Hazard ratios of breast conserving therapy vs. mastectomy with post-operative radiation therapy on 10-year overall, relative and distant metastasis-free survival in T1−2N2 breast cancer Cohort Hazard ratio (95% confidence interval) 2000–2004 cohort (n = 3,701) 2003 cohort (n = 594) Overall survival Relative survival Distant metastasis-free survival Overall cohort MAST + RT 1 1 1 BCT 0.88 (0.77–0.99) 0.89 (0.75–1.04) 0.87 (0.64–1.18) T1N2 MAST + RT 1 1 1 BCT 0.83 (0.68–1.01) 0.81 (0.62–1.05) 1.15 (0.69–1.93) T2N2 MAST + RT 1 1 1 BCT 0.82 (0.71–0.96) 0.81 (0.67–0.97) 0.75 (0.51–1.11) Hazard ratios in bold are considered significant (p < 0.05). All hazard ratios are corrected for relevant confounders. Conclusions: BCT is associated with at least equal 10-year OS, RS and DMFS compared to MAST with RT in T1−2N2 breast cancer. Therefore, BCT in T1−2N2 breast cancer is preferred if feasible and appropriate.