Utility of [18F]FDG PET/CT in predicting pathological complete response to neoadjuvant therapy in breast cancer: A prospective study.
Authors: Gelardi Fabrizia , Sollini Martina , Zanca Roberta , Tiberio Paola , De Sanctis Rita , Fernandes Bethania , Rodari Marcello , Chiti Arturo , Antunovic Lidija , Santoro Armando 
Published: June 2024

3070 Background: The achievement of a pathological complete response (pCR) to neoadjuvant chemotherapy (NAC) is a major milestone in the treatment of breast cancer (BC), offering an improved prognosis. The new revolutionary frontier is to potentially eliminate the need for surgery in selected cases with an excellent response to NAC. This approach would lead to improved patient outcomes and cost effectiveness. The current standard for assessing residual cancer after NAC is to perform an invasive procedure and biopsy. In this study, we investigate the utility of [18F]FDG PET/CT as a predictive tool for pCR following NAC in BC patients. Methods: We conducted a prospective study of patients with newly diagnosed BC who underwent NAC, with [18F]FDG PET/CT assessment at baseline and after NAC prior to surgery. Clinical and pathological data were collected, with response to NAC categorised as pCR or non-pCR based on definitive histopathology, supplemented by assessment using the Residual Cancer Burden (RCB) index. Semi-quantitative parameters including SUVmax and tumour to background ratio (TBRmax) were calculated for the primary tumour at baseline and preoperative PET/CT scans. Differences between groups were assessed using the Kruskal-Wallis test. Correlations between outcomes and potential predictors were explored using multivariate logistic regression analyses. Statistical significance was set at p <0.05. Results: Our study cohort comprised 134 BC patients with a median age of 49.5 years, predominantly HER-2 positive (n=74) and stage II disease (n=104). Of these, 69 patients achieved pCR after NAC. The RCB index was assessed in 94/134 patients, showing varying degrees of residual disease burden (59 RCB-0; 5 RCB-I; 24 RCB-II; 6 RCB-III). Baseline SUVmax and TBRmax showed correlations with key tumour characteristics, including BC subtype (TBRmax was 9.56 vs 5.6 vs 10.2 in luminal, HER-2+ and TNBC, respectively; p=0.005) and ki-67 expression (rho 0.32, p=0.002). However, baseline SUV and TBR parameters failed to discriminate responders to NAC. Conversely, preoperative TBRmax showed significant associations with both pCR (1.09 vs 1.75 for pCR and non-pCR; p<0.001) and RCB index (1.09 vs 1.21 vs 1.32 vs 4.25 for RCB-0, I, II, III; p<0.001). Logistic multivariate analysis identified TBRmax as a significant predictor of pCR both at baseline (OR 1.07, p=0.04) and at preoperative assessment (OR 0.2, p<0.001). In addition, preoperative TBRmax emerged as a significant predictor of response based on the RCB index (OR 5.5, p=0.004). Conclusions: Our research shed light on the significant clinical utility of semi-quantitative parameters derived from [18F]FDG PET/CT scans in predicting pCR in BC patients undergoing NAC, potentially advancing the frontiers of BC management and encouraging its integration into the decision-making framework for assessing response to NAC.