Apparent diffusion coefficient as a potential surrogate marker for Ki-67 index in mucinous breast carcinoma

Purpose To examine the association between apparent diffusion coefficient (ADC), cellularity, and Ki-67 index in mucinous breast carcinoma (MBC) compared with invasive carcinoma of no special type (NST). ADC's ability to identify lesions with highly proliferating MBC was also examined. Materials and Methods Pathologically confirmed MBCs (mucinous group, n = 18) and NSTs (control group, n = 18) were retrospectively analyzed. ADC was calculated from signal intensity of diffusion-weighted imaging at b values of 0 and 1000 sec/mm2. The Ki-67 index and cellularity were histopathologically evaluated. The mucinous group was classified into high Ki-67 mucinous group (Ki-67 index ≥14%, highly proliferating) and low Ki-67 mucinous group. Results In the mucinous group, minimum ADC (ADCmin) showed an inverse correlation with cellularity (r = −0.802, P < 0.0001) and Ki-67 index (r = −0.825, P < 0.0001). In the control group, ADCmin showed inverse correlation with cellularity (r = −0.537 P = 0.022), but no correlation with Ki-67 index (r = 0.035, P = 0.892). ADCmin of high Ki-67 mucinous group was significantly lower than that of low Ki-67 mucinous group (P = 0.005). Conclusion This study demonstrates an inverse correlation between ADC and Ki-67 index in MBC and the ability of ADC to identify highly proliferating MBC. Considering that ADC can evaluate whole lesions noninvasively, ADC may be a promising noninvasive surrogate marker for Ki-67 index in the risk stratification of MBC. J. Magn. Reson. Imaging 2015;41:610–615. © 2014 Wiley Periodicals, Inc.