Nonmass lesions on preoperative MRI in breast cancer patients: clinical implications and prognostic significance.

This study aimed to investigate the clinical importance and prognostic value of nonmass lesions (NMLs) identified via preoperative magnetic resonance imaging (MRI) in patients with breast cancer, with an emphasis on understanding how these lesions affect treatment decisions and survival outcomes. A retrospective analysis was conducted on 6971 patients diagnosed with breast cancer who underwent surgery at Asan Medical Center, Seoul, between January 2000 and December 2021. Patients were categorized based on the presence or absence of NMLs on preoperative MRI. Various clinicopathological parameters were compared, and survival outcomes, such as overall survival (OS), distant metastasis-free survival (DMFS), regional recurrence-free survival (RFS), and local recurrence-free survival (LFS), were analyzed using Kaplan-Meier and Cox regression methods. Subgroup analyses were performed based on the type of surgery and the administration of neoadjuvant chemotherapy and adjuvant radiation therapy. Of the total cohort, 21.9% (n = 1524) had NMLs. The presence of NMLs was associated with a significant improvement in OS (P = 0.017) for the entire patient group. Multivariate analysis revealed the presence of NMLs as a favorable prognostic factor (hazard ratio 0.47, 95% confidence intervals 0.25-0.90, P = 0.022). Subgroup analyses demonstrated significantly improved OS, DMFS, and RFS outcomes for patients with NMLs who underwent mastectomy after neoadjuvant chemotherapy. NMLs on preoperative MRI in patients with breast cancer are associated with improved overall survival (OS) and serve as an independent prognostic factor. However, further research is needed to elucidate the underlying reasons for these outcomes.