Purpose: To use pathologic indicators to determine which patients benefit from postmastectomy radiation therapy (PMRT) for breast cancer after neoadjuvant chemotherapy (NACT) and total mastectomy (TM). Patients and methods: We enrolled 4236 patients with breast invasive ductal carcinoma who received NACT followed by TM. Cox regression analysis was used to calculate hazard ratios (HRs) and confidence intervals; independent predictors were controlled for or stratified in the analysis. Results: After multivariate Cox regression analyses, the adjusted HRs derived for PMRT for all-cause mortality were 0.65 (0.52–0.81, P < 0.0001) and 0.58 (0.47–0.71, P < 0.0001) in postchemotherapy pathologic tumor stages T2–4 (ypT3–4) and postchemotherapy pathologic nodal stages N2–3 (ypN2–3), respectively. Moreover, adjusted HRs derived for PMRT with all-cause mortality were 0.51 (0.38–0.69, P < 0.0001), 0.60 (0.40–0.88, P = 0.0096), and 0.64 (0.48–0.86, P = 0.0024) in pathological stages IIIA, IIIB, and IIIC, respectively. Additionally, the PMRT group showed significant locoregional control irrespective of the pathologic response, even ypT0, ypN0, or pathological complete response (pCR), compared with the No-PMRT group. The multivariate analysis showed no statistical differences between the PMRT and No-PMRT groups for distant metastasis-free survival in any pathologic response of ypT0–4, ypN0–3, and pathologic American Joint Committee on Cancer stages pCR to IIIC. Conclusion: For patients with breast cancer ypT3–4, ypN2–3, or pathologic stages IIIA–IIIC receiving NACT and TM, benefit from PMRT if it is associated with OS benefits, regardless of the clinical stage of the disease. Compared with No-PMRT, PMRT improved locoregional recurrence-free survival, even pCR, in patients with breast cancer receiving NACT and TM.
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