Abstract PS4-11-03: Prognostic impact of PET and/or breast MRI radiological response in early breast cancer patients undergoing neoadjuvant chemotherapy

Abstract Purpose: Pathological complete response (pCR) to neoadjuvant chemotherapy (NACT) is the most relevant prognostic factor for patients with early breast cancer (eBC). However, the prognostic value of complete radiological response assessed by PET and/or breast MRI (bMRI) following NACT remains unclear. In this study, we investigated the potential prognostic significance of radiological complete response (rCR) in patients with eBC undergoing NACT. Methods: We retrospectively identified patients with eBC receiving NACT at the University Hospital of Parma between 2018 and 2022. Data about radiological response in terms of rCR, partial response and disease progression/stable disease and about pCR were collected. We used Kaplan-Meier curves to analyze relapse-free survival (RFS) and overall survival (OS) based on radiological response in the overall population and after excluding patients with Luminal eBC. Comparisons between groups were performed with log-rank test. Cox regression models were used to determine independent predictive role of rCR for RFS and OS, corrected by age, lymph nodes status and pCR. Results: Overall, 120 patients were included in the analysis. The mean age at diagnosis of the study population was 49.4 ± 9.84 years. 58 patients (48.3%) had positive lymph nodes at diagnosis. 38 patients (31.7%) had triple negative BC (TNBC), 47 patients (39.1%) had HER2-positive BC, 35 patients (29.2%) had Luminal BC. Median follow up time was 49 months (IQR 42.1-58.8). At 48 months-follow up, 63.5% of patients without any CR, 96.3% of patients who achieved CR on both PET and bMRI and 97.4% of patients with CR on at least PET or bMRI were alive. Moreover, 47.6% of patients without any CR, 96.3% of patients who achieved CR on both PET and bMRI and 97.4% of patients with CR on at least PET or bMRI were recurrence-free. rCR on at least one radiological assessment was independently associated with better RFS aHR 0.24 (95% CI, 0.09-0.62, p = 0.003) and OS aHR 0.24 (95% CI, 0.06-0.91, p = 0.035). No patients who failed to achieve rCR on both PET and bMRI achieved pCR. In TNBC, 13 out of 19 patients (68.4%) with CR on both PET/bMRI obtained pCR, 3 out of 9 patients (33.3%) with CR on at least PET or bMRI obtained pCR (p = 0.002). In HER2-positive BC, 20 out of 27 patients (74.1%) with CR on both PET/bMRI obtained pCR, 7 out of 16 patients (43.8%) with CR on at least PET or bMRI obtained pCR (p = 0.008). In Luminal BC, 3 out of 8 patients (37.5%) with CR on both PET/bMRI obtained pCR, 2 out of 14 patients (14.3%) with CR on at least PET or bMRI obtained pCR (p = 0.0058). Considering only the 85 patients affected by TNBC and HER2-positive BC, RFS and OS were statistically significantly better in patients with rCR on at least one radiological assessment aHR 0.23 (95% CI, 0.07-0.71, p = 0.011 and HR 0.16 (95% CI, 0.03-0.78, p = 0.024, respectively. Conclusions: rCR on PET and/or bMRI following NACT is a strong prognostic marker for improved survival in eBC, particularly in TNBC and HER2-positive subtypes. This benefit appears to be independent of achieving pCR, highlighting the potential of imaging response as an additional tool for risk stratification and treatment decision-making in clinical practice. Citation Format: M. Corianò, C. Tommasi, G. Reni, A. Ingallinella, C. Tornali, F. Pratticò, M. Baronchelli, E. Cardinale, M. Scarlattei, C. Cidda, E. Spaggiari, E. Martella, G. Di Maria, A. Cosenza, D. Boggiani, D. Zanoni, C. D'Aloia, E. Silini, L. Ruffini, B. Pellegrino. Prognostic impact of PET and/or breast MRI radiological response in early breast cancer patients undergoing neoadjuvant chemotherapy abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-11-03.