Breast Cancer: Influence of Taxanes on Response Assessment with Dynamic Contrast-enhanced MR Imaging

Purpose: To prospectively investigate the influence of taxane-containing neoadjuvant chemotherapy (T-NACT) versus non-taxane-containing NACT (NT-NACT) on the contrast material enhancement of breast cancers, benign enhancing lesions (BELs), and background parenchymal enhancement (BPE) at dynamic contrast-enhanced magnetic resonance (MR) imaging. Materials and Methods: This institutional review board-approved study was performed in 62 patients with invasive breast cancer who underwent multiagent NACT with (n = 49) or without (n = 13) taxanes between 2008 and 2011. Written informed consent was obtained. Patients underwent dynamic contrast-enhanced MR imaging according to a standardized protocol before and 2 weeks after completing NACT. The percentage reduction of enhancement of breast cancers, BELs, and BPEs was calculated for patients undergoing NT-NACT versus those undergoing T-NACT. Final surgical pathologic results served as standard of reference. Changes in mean enhancement of breast cancers, BELs, and BPEs between the regimens were compared by using the Student t test for unpaired samples; for intraindividual comparison, the Student t test for paired samples was used. Results: Similar rates of complete pathologic response were observed after T-NACT and NT-NACT (28 [57.2%] of 49 vs eight [61.5%] of 13). T-NACT was associated with an almost complete suppression of enhancement in not only breast cancers but also BELs and BPE in the same patients, with an average reduction of enhancement of -89.9% +/- 9.3, -90.2% +/- 11.8, and -91.2% +/- 7.5, respectively. After T-NACT, cancers with partial (n = 21) or complete (n = 28) pathologic response exhibited a similar reduction of enhancement (-81.8% +/- 17.5 vs -93.9% +/- 2.3; P = .22). The reduction of enhancement of cancers after NT-NACT was significantly less pronounced than that after T-NACT (-41.1% +/- 22.8 vs 88.1% +/- 13.9; P < .0001), and effects on enhancement of BELs and BPE were significantly less pronounced compared with effects on enhancement of cancers in the same women (P,.0001). MR imaging led to an overestimation of response (yielded false-negative results for residual disease) in 66.7% (14 of 21) of patients after T-NACT, versus in 20% (one of five) of patients after NT-NACT. Conclusion: The reduction of enhancement observed in breast cancers after T-NACT is, in part, unrelated to their oncologic response. MR imaging-detectable effects of taxanes represent a combination of specific antimitotic and nonspecific antian-giogenic effects. This impacts the accuracy with which dynamic contrast-enhanced MR imaging helps predict complete pathologic response to T-NACT. (C) RSNA, 2015