Impact of Preoperative Breast MR Imaging and MR-guided Surgery on Diagnosis and Surgical Outcome of Women with Invasive Breast Cancer with and without DCIS Component

Purpose To (a) compare the diagnostic accuracy of breast magnetic resonance (MR) imaging with that of conventional imaging (digital mammography and breast ultrasonography) in the identification of ductal carcinoma in situ (DCIS) components of biopsy-proven invasive breast cancer before surgery and (b) investigate the surgical outcome (positive margin rates and mastectomy rates) of women with breast cancer who underwent preoperative MR imaging combined with MR-guided needle biopsy and/or MR-guided lesion localization or bracketing where appropriate. Materials and Methods The authors performed a prospective two-center study of 593 consecutive patients with biopsy-proven invasive breast cancer who underwent breast MR imaging in addition to conventional imaging. MR-guided vacuum biopsy and MR-guided lesion bracketing were performed for DCIS components visible at MR imaging alone. The accuracy of breast MR imaging was compared with that of conventional imaging, and surgical outcomes (positive margin and mastectomy rates) were investigated. Results Surgical-pathologic assessment demonstrated DCIS components in 139 of the 593 women (23.4%). The sensitivity of MR imaging for the diagnosis of DCIS components pre-operatively (84.9%; 118 of 139) was significantly higher than that of conventional imaging (36.7%; 51 of 139) (P < .0001); more than half of DCIS components (51.1%; 71 of 139) were detected only with MR imaging. The sensitivity advantage of MR imaging over conventional imaging increased with increasing relative size of DCIS components, as follows: The sensitivity of MR imaging versus conventional imaging for small, marginal DCIS components was 56.8% (21 of 37) versus 29.7% (11 of 37); the sensitivity for extensive DCIS components was 91.7% (55 of 60) versus 41.7% (25 of 60); the sensitivity for large, predominant DCIS components was 100.0% (42 of 42) versus 35.7% (15 of 42). Moreover, the sensitivity advantage of MR imaging over conventional imaging increased with increasing nuclear grade of DCIS components, as follows: The sensitivity of MR imaging versus conventional imaging for low-grade DCIS components was 74.0% (20 of 27) versus 40.7% (11 of 27); the sensitivity for intermediate-grade DCIS components was 84.1% (53 of 63) versus 34.9% (22 of 63); the sensitivity for high-grade DCIS components was 91.8% (45 of 49) versus 36.7% (18 of 49) (P < .05-.001 for all). Positive margin rates were low overall (3.7% [95% Clopper Pearson confidence interval [CI]: 2.3%, 5.6%]) and did not differ significantly between the 139 women with DCIS components (5.0% [95% CI: 2.0%, 10.1%]) compared with the 454 women without such components (3.3% [95% CI: 1.9%, 5.4%]). The same was true for mastectomy rates (10.8% [95% CI: 6.2%, 17.2%] vs 8.1% [95% CI: 5.8%, 11.1%]). Conclusion Breast MR imaging improves depiction of DCIS components of invasive breast cancers before surgery and is associated with positive margin and mastectomy rates that are low irrespective of the presence or absence of DCIS components. © RSNA, 2017.