Quantitative Apparent Diffusion Coefficients From Peritumoral Regions as Early Predictors of Response to Neoadjuvant Systemic Therapy in Triple‐Negative Breast Cancer

Background Pathologic complete response (pCR) to neoadjuvant systemic therapy (NAST) in triple‐negative breast cancer (TNBC) is a strong predictor of patient survival. Edema in the peritumoral region (PTR) has been reported to be a negative prognostic factor in TNBC. Purpose To determine whether quantitative apparent diffusion coefficient (ADC) features from PTRs on reduced field‐of‐view (rFOV) diffusion‐weighted imaging (DWI) predict the response to NAST in TNBC. Study Type Prospective. Population/Subjects A total of 108 patients with biopsy‐proven TNBC who underwent NAST and definitive surgery during 2015–2020. Field Strength/Sequence A 3.0 T/ rFOV single‐shot diffusion‐weighted echo‐planar imaging sequence ( DWI ). Assessment Three scans were acquired longitudinally (pretreatment, after two cycles of NAST, and after four cycles of NAST). For each scan, 11 ADC histogram features (minimum, maximum, mean, median, standard deviation, kurtosis, skewness and 10th, 25th, 75th, and 90th percentiles) were extracted from tumors and from PTRs of 5 mm, 10 mm, 15 mm, and 20 mm in thickness with inclusion and exclusion of fat‐dominant pixels. Statistical Tests ADC features were tested for prediction of pCR, both individually using Mann–Whitney U test and area under the receiver operating characteristic curve (AUC), and in combination in multivariable models with k‐fold cross‐validation. A P value < 0.05 was considered statistically significant. Results Fifty‐one patients (47%) had pCR. Maximum ADC from PTR, measured after two and four cycles of NAST, was significantly higher in pCR patients (2.8 ± 0.69 vs 3.5 ± 0.94 mm 2 /sec). The top‐performing feature for prediction of pCR was the maximum ADC from the 5‐mm fat‐inclusive PTR after cycle 4 of NAST (AUC: 0.74; 95% confidence interval: 0.64, 0.84). Multivariable models of ADC features performed similarly for fat‐inclusive and fat‐exclusive PTRs, with AUCs ranging from 0.68 to 0.72 for the cycle 2 and cycle 4 scans. Data Conclusion Quantitative ADC features from PTRs may serve as early predictors of the response to NAST in TNBC. Evidence Level 1 Technical Efficacy Stage 4