Added value of mean and entropy of apparent diffusion coefficient values for evaluating histologic phenotypes of invasive ductal breast cancer with MR imaging

ObjectivesTo study the added value of mean and entropy of apparent diffusion coefficient (ADC) values at standard (800 s/mm(2)) and high (1500 s/mm(2)) b-values obtained with diffusion-weighted imaging in identifying histologic phenotypes of invasive ductal breast cancer (IDC) with MR imaging.MethodsOne hundred thirty-four IDC patients underwent diffusion-weighted imaging with b-values of 800 and 1500 s/mm(2), and corresponding ADC(800) and ADC(1500) maps were generated. Mean and entropy of volumetric ADC values were compared with molecular markers (estrogen receptor [ER], progesterone receptor [PR], human epidermal growth factor receptor 2 [HER2], and Ki-67). Associations among morphologic features, ADC metrics, and phenotypes (luminal A, luminal B [HER2 negative], luminal B [HER2 positive], HER2 positive, and triple negative) were evaluated.ResultsMean ADC values were significantly decreased in ER-positive, PR-positive, and HER2-negative tumors (p < 0.01). Ki-67 20% tumors demonstrated significantly higher ADC entropy values compared with Ki-67 < 20% tumors (p < 0.001). Luminal A subtype tended to display lower ADC entropy values compared with other subtypes, while HER2-positive subtype tended to display higher mean ADC values. ADC(1500) entropy provided superior diagnostic performance over ADC(800) entropy (p = 0.04). Independent risk factors were ADC(1500) entropy (p = 0.002) associated with luminal A, irregular mass shape (p = 0.018) and ADC(1500) entropy (p = 0.022) with luminal B (HER2 positive), mean ADC(1500) (p = 0.018)with HER2 positive, and smooth mass margin (p = 0.012) and rim enhancement (p = 0.003) with triple negative.ConclusionsMean and entropy of ADC values provided complementary information and added value for evaluating IDC histologic phenotypes. High-b-value ADC(1500) may facilitate better phenotype discrimination.Key Points center dot ADC metrics are associated with molecular marker status in IDC.center dot ADC(1500)improves differentiation of histologic phenotypes compared with ADC(800).center dot ADC metrics add value to morphologic features in IDC phenotyping.