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 3071 patients

PURPOSE: Our previous study demonstrated breast-conserving surgery with radiation therapy (BCT) to be at least equivalent to mastectomy in T1-2N0-1 breast cancer. Yet, 10-year survival rates after BCT and mastectomy with radiation therapy (MAST) in T1-2N2 breast cancer specifically have not been examined. Our study aimed to determine 10-year overall (OS), relative (RS), and distant metastasis-free survival (DMFS) in T1-2N2 breast cancer after BCT and MAST, stratified for T category. METHODS: All women diagnosed with primary invasive T1-2N2 breast cancer in 2000-2004, treated with BCT or MAST, both with axillary dissection and RT, were selected from the Netherlands Cancer Registry. Ten-year OS and DMFS were estimated using multivariable Cox regression. Excess mortality ratios (EMR) were calculated to estimate RS, using life tables of the general population. OS and RS were determined on the whole cohort, and DMFS on the 2003 cohort with completed follow-up. Missing data were imputed. RESULTS: Of 3071 patients, 1055 (34.4 %) received BCT and 2016 (65.7 %) MAST. BCT and MAST showed equal 10-year OS and RS. After stratification, BCT was significantly associated with improved 10-year OS [HRadjusted 0.82 (95 % CI 0.71-0.96)] and RS (EMRadjusted 0.81 (95 % CI 0.67-0.97]) in T2N2, but not in T1N2. Ten-year DMFS was equal for both treatments [HRadjusted 0.87 (95 % CI 0.64-1.18)] in the 2003 cohort (n = 594), which was representative for the full cohort. CONCLUSION: BCT showed at least equal 10-year OS, RS, and DMFS compared to MAST. These results confirm that BCT is a good treatment option in T1-2N2 breast cancer