Histogram Analysis of Apparent Diffusion Coefficient at 3.0T: Correlation With Prognostic Factors and Subtypes of Invasive Ductal Carcinoma

Purpose: To evaluate apparent diffusion coefficient (ADC) histogram parameters that show correlations with prognostic factors and subtypes of breast cancer. Materials and Methods: At 3.0T, various ADC histogram parameters were calculated including the entire tumor volume in 173 invasive ductal carcinomas: the minimum, 10th percentile, mean, median, 90th percentile, and maximum. ADC parameters were correlated with prognostic factors and subtype. Results: The mean ADC(median) value was significantly higher in the group with lymph node metastasis, HER2 positivity, and a Ki-67 value < 14% than in the group with negativity for lymph node metastasis, HER2 negativity, and a Ki-67 value >= 14% (0.907, 0.978, and 0.941 vs. 0.735, 0.778, and 0.761 3 10(-3) mm(2)/s, respectively) (P< 0.01). There was no significant correlation between ADC(median) and tumor size, histologic grade, estrogen receptor expression, and progesterone receptor expression (P=0.272, 0.113, 0.261, and 0.181, respectively). For most ADC parameters except for ADC(min), the mean of variable ADC parameters of HER2-positive, luminal A, luminal B-HER2(+), triple-negative, and luminal BHER2(-) diseases were arranged in descending order (1.175, 0.936, 0.863, 0.811, and 0.665 x 10(-3) mm(2)/s in ADC(median), respectively) with statistical significant difference (P< 0.001). In multivariate analysis, histologic grade, the Ki-67 index, and HER2 expression were statistically significant explanatory prognostic factors for ADCmedian and the Ki-67 index had the most robust effects on ADC parameters (standardized coefficient = -0.317). Conclusion: Various ADC parameters were correlated with prognostic factors and subtype, except for ADC(min). HER2 positivity showed high ADC values and high Ki-67 index revealed low ADC values.