To assess whether pre- and intra-treatment simultaneous 18F-FDG PET/MRI could be useful in the prediction of the response to neoadjuvant chemotherapy (NAC) in breast cancer (BC) patients.

Between January 2017 and January 2020, 37 consecutive patients (mean age 45 ± 15 yrs) with 41 histologically proven BC lesions, candidate to anthracycline- and taxane-based NAC were prospectively enrolled. Simultaneous breast 18F-FDG PET/MRI examination was performed twice in each patient, one week before NAC and after the second anthracycline administration. PET/MRI images were analyzed to extract quantitative diffusion (ADCmin, ADCmean), perfusion (Ktrans, Kep, Ve, IAUC) and metabolic (SUV2D, SUV3D, MTV) parameters. The variation of each parameter (delta, ?) after the second anthracycline cycle was then calculated. Univariate analysis through Mann-Whitney U test was performed to assess differences in terms of pre-treatment and ? parameters between patients who showed complete and partial response (CR, PR) at histological examination after NAC. Multivariate logistic regression analysis was then used to identify imaging parameters predictive of CR.

At Mann Mann-Whitney U test, significant differences were found between patients with PR and CR after NAC in terms of ?-Ve (p=0.016), SUV3D (p=0.022) and SUV2D (p=0.043). In detail, the early post-treatment variation of Ve was significantly higher in patients who showed CR after NAC. Furthermore, patients with CR showed higher pre-treatment SUV3D and SUV2D compared to patient with PR after NAC. At multivariate logistic regression, both ?-Ve and SUV3D resulted independent predictors of complete response to NAC, with p values of 0.013 and 0.021, respectively.

Simultaneoubreast PET/MRI could be useful to early predict the response to NAC in patientwith BC. Our preliminary observationshow that functional parameter(i.e. perfusion and metabolic)may identify patientwho will respond completely, particularly using both pre-treatment and the variation of quantitative parameterearly after the second cycle of NAC.

Simultaneous breast PET/MRI may be useful for early identification of BC patients who would benefit from continuing NAC or for whom surgical excision could be optionally considered.