Comparing irradiated clinical outcomes between modified radical mastectomy and breast-conserving surgery in patients with pathologic stage III breast cancer: A national population-based match cohort study.

BACKGROUND

Limited data are available for comparing irradiated clinical outcomes between modified radical mastectomy and breast-conserving surgery for patients with pathologic stage III breast cancer, especially when stratified by molecular subtypes.

METHODS

The present population-based cohort study used the Taiwan National Health Insurance Research Database. Patients with pathologic stage III breast cancer who underwent breast-conserving surgery plus radiotherapy or modified radical mastectomy plus radiotherapy from 2006 to 2019 were included in data analysis. The baseline characteristics of the breast-conserving surgery plus radiotherapy and modified radical mastectomy plus radiotherapy groups were matched using propensity scores, with exact matching for the molecular subtypes of breast cancer between the 2 groups. Local-regional recurrence, distant metastasis, disease-free survival, and overall survival as the primary outcomes were assessed using Fine and Gray's competing-risk regression model, stratified by breast cancer subtypes.

RESULTS

A total of 5,166 patients who underwent breast-conserving surgery plus radiotherapy (n = 2,583) and modified radical mastectomy plus radiotherapy (n = 2,583) were included. Overall, our results showed a lower incidence of local-regional recurrence with modified radical mastectomy plus radiotherapy than with breast-conserving surgery plus radiotherapy (0.6% vs 1.9%, P = .001; adjusted hazard ratio, 0.33; P = .0002). However, no difference was observed in the rates of distant metastasis, disease-free survival, and overall survival between the breast-conserving surgery plus radiotherapy and modified radical mastectomy plus radiotherapy groups. Notably, among those with luminal breast cancer, the risk of local-regional recurrence was lower in patients who underwent modified radical mastectomy plus radiotherapy than those who underwent breast-conserving surgery plus radiotherapy, with an adjusted hazard ratio of 0.28 (P = .022). For patients with human epidermal growth factor receptor 2-positive breast cancer, a lower risk of local-regional recurrence was observed in modified radical mastectomy + radiotherapy compared with breast-conserving surgery plus radiotherapy, with an adjusted hazard ratio of 0.06 (P = .0018). However, for triple-negative breast cancer, no differences were observed between the 2 groups in terms of local-regional recurrence, distant metastasis, disease-free survival, and overall survival.

CONCLUSION

Our findings indicated that modified radical mastectomy + radiotherapy offers a greater advantage in reducing the risk of local-regional recurrence compared with breast-conserving surgery plus radiotherapy in patients with pathologic stage III breast cancer, particularly those with luminal or human epidermal growth factor receptor 2-positive molecular subtypes. However, this advantage is not observed in other clinical outcomes, such as, distant metastasis, disease-free survival, and overall survival, and it does not have a significant effect in patients with triple-negative breast cancer. Further randomized controlled trials are necessary to establish robust clinical evidence.