High-Risk pT1-2N0 Breast Cancer may Benefit from Postmastectomy Radiotherapy: A Risk Stratification Analysis Based on Nomogram

Abstract

<h3>Purpose/Objective(s)</h3> Postmastectomy radiation therapy (PMRT) had heterogeneous effects on clinical outcome of patients with pT1-2N0 breast cancer. We aimed to develop nomograms for predicting locoregional recurrence-free survival (LRRFS) and disease-free survival (DFS), and to explore the potential effect of PMRT in pT1-2N0 breast cancer. <h3>Materials/Methods</h3> Clinical data were collected from 840 patients with newly diagnosed pT1-2N0 breast cancer between January 2015 and December 2018. Nomograms predicting the LRRFS and DFS rates were developed based on the risk factors identified by Cox regression analysis in patients treated with mastectomy alone (n =671). Furthermore, the effect of PMRT was indirectly investigated by comparing patients treated with mastectomy alone with those treated with breast-conserving surgery (BCS) plus radiotherapy (n =169) in different risk subgroups stratified by the nomogram scores. The optimal cut-off points were identified by X-tile software. LRRFS and DFS were evaluated using the Kaplan-Meier method, and the differences were compared using the log-rank test. Propensity score matching analysis (PSM) was performed to balance the backgrounds of patients between the mastectomy alone and BCS plus radiotherapy sets. <h3>Results</h3> After a median follow-up duration of 62 months (range, 9–79 months) and 50 months (range, 10–79 months) in the mastectomy alone and BCS plus radiotherapy sets, respectively. The 5-year LRRFS rates (97.0% vs. 97.3%, P = 0.516) and the 5-year DFS rates (92.0% vs. 92.7%, P = 0.339) were similar between the mastectomy alone and BCS plus radiotherapy sets, respectively. Multivariate Cox regression showed that larger tumor size, high grade, and hormone receptor (HR)-negative status were independent poor prognostic factors for both LRRFS and DFS (P<0.05 for all), while premenopausal status was independently associated with worse LRRFS (P=0.019). Incorporation of these factors into the constructed nomograms showed high accuracy when predicting the 5-year LRRFS and DFS rates, with concordance indexes of 0.794 (95%CI: 0.704-0.884) and 0.726 (95%CI: 0.659-0.793), respectively, after internal validation. Based on nomogram scores, patients were classified into different risk groups. After PSM in subgroups, compared with mastectomy alone, BCS plus radiotherapy significantly improved the LRRFS (84.9% vs. 96.6%, p = 0.026) and DFS (71.8% vs. 100%, p = 0.033) in the high-risk group, but not in the low-risk or intermediate-risk group (P>0.05 for all). <h3>Conclusion</h3> The constructed nomograms can not only estimate the individualized 5-year LRRFS and DFS rates among patients with pT1-2N0 breast cancer after mastectomy but can also stratify patients into different risk subgroups, and thus, they can help identify high-risk patients who are more likely to benefit from PMRT.