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/mm(2) . 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.
(© 2014 Wiley Periodicals, Inc.)