Multiparametric MRI to predict response to neoadjuvant chemotherapy in breast cancer: Are we ready for NacBI-RADS?

Objectives Accurate assessment of treatment response to neoadjuvant chemotherapy (NAC) in breast cancer (BC) is crucial for guiding surgical planning. While size-based criteria remain standard, they may underestimate therapy-induced biological changes. To develop and validate the neoadjuvant breast imaging reporting and data system (NacBI-RADS), a structured multiparametric MRI (mp-MRI) lexicon was designed to evaluate NAC response and support surgical decision-making. Materials and methods This retrospective study included 68 BC patients who underwent staging and post-NAC MRI, followed by surgery. mp-MRI examinations included contrast-enhanced T1, T2-weighted, and diffusion-weighted imaging. NacBI-RADS integrates four parameters: peritumoral edema, ΔADC (apparent diffusion coefficient change), post-contrast tumor size, and lymph node status (Node-RADS). Three independent breast radiologists evaluated all cases. Inter-reader agreement was assessed with Cohen’s and Fleiss’ kappa. Results Of 88 patients assessed, 68 were included. Residual disease was found in 43 patients (63%) and pathological complete response in 25 (37%). Most lesions were categorized as NacBI-RADS 1–2, while categories 4–5 were less frequent (12–15%). NacBI-RADS showed high diagnostic performance (AUC 0.942–0.960) with excellent reproducibility (κ 0.931–0.953). Lower categories were associated with complete or near-complete response, and higher categories with residual disease ( p < 0.001). Conclusion This exploratory study suggests that NacBI-RADS may offer a standardized and reproducible mp-MRI framework for assessing NAC response. Further studies are needed to confirm its role in imaging-guided surgical planning. Key Points Question Can a structured mp-MRI framework improve the accuracy and reproducibility of assessing BC response to NAC compared with conventional size-based criteria ? Findings NacBI-RADS showed high diagnostic accuracy (AUC up to 0.960) and excellent inter-reader agreement, reliably distinguishing complete/partial-complete responders from patients with residual disease . Clinical relevance NacBI-RADS may support more accurate and reproducible response assessment after NAC, helping identify true complete responders and aiding safe, personalized surgical de-escalation strategies in BC management .