Postmastectomy radiotherapy (PMRT) is well established in patients with ≥4 positive axillary lymph nodes (ALN); indications in 1 to 3 positive ALN remains controversial. We examined clinicopathologic criteria used for PMRT selection and compared locoregional recurrence (LRR), recurrence-free survival (RFS), and overall survival (OS) among patients with and without PMRT.

Between 1995 and 2006, a total of 1,331 patients with T1-T2 tumors and 1 to 3 positive ALN underwent mastectomy. We excluded T3/T4 tumors and neoadjuvant chemotherapy; we analyzed 1,087 patients (924 without PMRT, 163 with PMRT). Chi square testing compared clinicopathologic features between groups. The Kaplan-Meier method and Cox regression analysis examined the association between PMRT and LRR, RFS, and OS.

PMRT patients were more likely to be ≤50 years old (p = 0.001) and to have larger tumors (p = 0.01), disease of a higher histologic grade (p = 0.03), lymphovascular invasion (LVI) (p < 0.0001), a greater number of positive ALN (p < 0.0001), extranodal invasion (p < 0.0001), and macroscopic ALN metastases (p < 0.0001). With a median follow-up of 7 years, PMRT and no-PMRT groups were similar in LRR (p = 0.57), RFS (p = 0.70), and OS (p = 0.28). On multivariate analysis of the no-PMRT group, age ≤50 years (p = 0.002) and presence of LVI (p < 0.0001) were associated with LRR. Stratified by age and LVI, patients ≤50 years old and with LVI had the highest 5-year LRR, 10.1 versus 1.1 %, than in patients >50 years old without LVI (p < 0.001).

By using clinicopathologic features, clinicians delivered PMRT to a select group of patients with T1-T2 tumors and 1 to 3 positive ALN, resulting in similarly low rates of 5-year LRR. Among patients not receiving PMRT, age ≤50 years and LVI were associated with increased LRR rates and warrant PMRT consideration.