The contrast‐free diffusion MRI multiple index for the early prediction of pathological response to neoadjuvant chemotherapy in breast cancer

Early tumor response prediction can help avoid overtreatment with unnecessary chemotherapy sessions. It is important to determine whether multiple apparent diffusion coefficient indices ( S index, ADC‐diff) are effective in the early prediction of pathological response to neoadjuvant chemotherapy (NAC) in breast cancer (BC). Patients with stage II and III BCs who underwent T 1 WI, diffusion‐weighted imaging (DWI), and dynamic contrast‐enhanced MRI using a 3 T system were included. They were divided into two groups: major histological responders (MHRs, Miller–Payne G4/5) and nonmajor histological responders (nMHRs, Miller–Payne G1–3). Three b values were used for DWI to derive the S index; ADC‐diff values were obtained using b = 0 and 1000 s/mm 2 . The different interquartile ranges of percentile S ‐index and ADC‐diff values after treatment were calculated and compared. The assessment was performed at baseline and after two and four NAC cycles. A total of 59 patients were evaluated. There are some correlations of interquartile ranges of S ‐index parameters and ADC‐diff values with histopathological prognostic factors (such as estrogen receptor and human epidermal growth factor receptor 2 expression, all p < 0.05), but no significant differences were found in some other interquartile ranges of S ‐index parameters or ADC‐diff values between progesterone receptor positive and negative or for Ki‐67 tumors (all P > 0.05). No differences were found in the dynamic contrast‐enhanced MRI characteristics between the two groups. HER‐2 expression and kurtosis of the S ‐index distribution were screened out as independent risk factors for predicting MHR group ( p < 0.05, area under the curve (AUC) = 0.811) before NAC. After early NAC (two cycles), only the 10th percentile S index was statistically significant between the two groups ( p < 0.05, AUC = 0.714). No significant differences were found in ADC‐diff value at any time point of NAC between the two groups ( P > 0.1). These findings demonstrate that the S ‐index value may be used as an early predictor of pathological response to NAC in BC; the value of ADC‐diff as an imaging biomarker of NAC needs to be further confirmed by ongoing multicenter prospective trials.