Effect of Postmastectomy Radiotherapy in Breast Cancer Patients according to Pathologic Nodal Status and Molecular Subtype after Neoadjuvant Chemotherapy

Purpose/Objective(s)

The role of post-mastectomy radiation therapy (PMRT) in breast cancer patients who have achieved ypN0 after neoadjuvant chemotherapy (NAC) has not yet been established. This study aimed to evaluate the benefit of PMRT according to pathologic node status and molecular subtype in breast cancer patients who were treated NAC.

Materials/Methods

We retrospectively reviewed 511 patients with clinical stage II-III breast cancer who underwent NAC and mastectomy at our institution from 2013 to 2017. After mastectomy, ypN+ and ypN0 were identified in 289 (56.6%) and 222 (43.4%), respectively. In this study, molecular subtypes were classified according to hormone receptor (HR) and HER2 receptors as follows: luminal (HR+/HER2-), luminal-HER2 (HR+/HER2+), HER2 enriched (HR-/HER2+), triple-negative (HR -/HER2-). All HER2-positive patients were treated with trastuzumab-containing NAC. Of the total patients, 448 (87.7%) received PMRT and 63 (12.3%) did not. In ypN+ patients, PMRT was performed in 265 (91.7%) and 24 (8.3%) did not. In ypN0 patients, PMRT was performed in 183 (82.4%) and 39 (17.6%) did not. The effect of PMRT on locoregional recurrence-free survival (LRRFS), disease-free survival (DFS), and overall survival (OS) was evaluated based on pathologic nodal status and molecular subtypes.

Results

The median follow-up duration was 58 months. The cumulative incidence of locoregional recurrence and distant metastasis were 11.8% and 31.5% in ypN+ patients, and 6.8% and 13.5% in ypN0 patients, respectively. In ypN+ patients, PMRT showed significant benefit for LRRFS, DFS, and OS in multivariate analysis (all P < 0.001). In ypN0 patients, triple-negative subtype and lymphovascular invasion were significant prognostic factors for LRRFS (all P < 0.001) and DFS (P = 0.002 and P < 0.001, respectively) by multivariate analysis. However, in ypN0 patients, PMRT was not significantly associated with LRRFS, DFS, and OS. In addition, PMRT showed no significant difference in LRRFS in all molecular subtypes of ypN0 patients.

Conclusion

PMRT should be performed in patients with residual lymph node following NAC and mastectomy. Although a limited number of patients, this study suggests that the role of PMRT in ypN0 patients regardless of subtype remains unclear.