Identify high-risk patients of T1-2N1M0 breast cancer who benefit from postmastectomy radiotherapy: a dual-center retrospective propensity score-matched study.

[OBJECTIVE] To develop a personalized risk stratification nomogram, integrating clinicopathological, sonographic, and mammographic features, to identify high-risk patients who may benefit from postmastectomy radiotherapy (PMRT).

[MATERIALS AND METHODS] A retrospective analysis was conducted on 408 patients from Medical Center 1 (January 2011 to June 2019) and 190 patients from Medical Center 2 (January 2017 to June 2019) with pathologically staged pT1-2N1M0 breast cancer following mastectomy, with preoperative mammography (MG) and ultrasound (US) imaging. After propensity score matching (PSM), the multimodal nomogram was developed using univariate and multivariate Cox regression analyses.

[RESULTS] With multivariate analysis, independent risk factors were identified, including age, pathologic T stage, positive axillary lymph nodes, lymphovascular invasion, microcalcifications, and vascularity on US, architectural distortion, and suspicious calcifications on MG (all p < 0.05). The C-index for the multimodal nomogram was 0.816 (95% CI: 0.774-0.859) in the training and 0.846 (95% CI: 0.772-0.920) in the external validation cohort, demonstrating superior prognostic accuracy, discriminative ability, and clinical applicability than clinicopathological and imaging-only models. Risk stratification using this nomogram showed that PMRT significantly improved RFS in the high-risk group (training cohort: HR = 0.392; external validation cohort: HR = 0.358, both p < 0.05), while patients in the low-risk group did not derive benefit from PMRT (training cohort: HR = 0.173; external validation cohort: HR = 0, both p > 0.05).

[CONCLUSION] This multimodal nomogram served as a clinical decision-support tool for clinicians to assess the risk-benefit balance of PMRT and had potential clinical application to guide further personalized adjuvant therapy for women with pT1-2N1M0 breast cancer.

[KEY POINTS] Question Can the multimodal nomogram integrating clinicopathological, ultrasonic, and mammographic parameters identify high-risk pT1-2N1M0 patients who may benefit from postmastectomy radiation therapy? Findings By effectively risk-stratifying, the nomogram identified high-risk patients who derived significant benefit from PMRT while distinguishing low-risk patients who could potentially avoid unnecessary treatment. Clinical relevance The multimodal nomogram served as a clinical decision-support tool for clinicians to optimize personalized adjuvant therapeutic approaches and improve survival outcomes for patients with pT1-2N1M0 breast cancer.