Background: Postmastectomy radiation (PMRT) in T1-T2 tumors with 1-3 positive axillary lymph nodes (ALNs) is controversial. Impact of molecular subtype (MST) on locoregional recurrence (LRR) and PMRT benefit is uncertain. We examined the association between MST and LRR, recurrence-free survival (RFS), and overall survival (OS), in T1-T2 tumors with 1-3 positive ALNs. Methods: From an institutional database, we identified mastectomy patients with 1-3 positive ALNs between 1995 and 2006. Patients who received neoadjuvant chemotherapy, had T3-T4 tumors, or ≥4 positive ALNs were excluded. MST was defined as: hormone receptor (HR)+/HER2-(luminal A/B), HR+/HER2+(luminal HER2), HR-/HER2+(HER2), and HR-/HER2-(basal). Kaplan-Meier method and Cox regression analysis were used to examine association between MST and LRR, RFS, and OS. Results: This study included 884 patients (700 no PMRT, 141 PMRT): 72.8 % luminal A/B, 7.8 % luminal HER2, 6.8 % HER2, and 12.6 % basal. Median follow-up was 6.3 years; 39 LRRs occurred. Luminal A/B subtype had the smallest tumors (p = 0.03), lowest intraductal component (p = 0.01), histologic grade (p < 0.0001), lymphovascular invasion (LVI) (p = 0.008), and multifocality/multicentricity (p = 0.02). On univariate analyses, there was no association between MST and LRR. MST was associated with RFS and OS; the basal and HER2 subtype had the lowest RFS (p = 0.0002) and OS (p < 0.0001). On multivariate analysis, only age ≤50 years (p = 0.003) and presence of LVI (p = 0.0003) were predictive of LRR; MST was not (p = 0.38). Conclusion: In patients with T1-T2 breast cancer and 1-3 positive lymph nodes who did not receive PMRT, MST was not an independent predictor of LRR and may not be useful in selecting PMRT candidates in that group.
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