Abstract S1-09: MRI screening of women at average risk of breast cancer

Abstract

Abstract Background: In asymptomatic women at average risk, screening mammography, possibly amended by breast ultrasound is recommended for early detection of breast cancer. Breast MRI is established for screening women at high familial risk, but there are no data available to support its use in women at average risk. Therefore, we systematically offered dynamic contrast enhanced breast MRI to asymptomatic women at average risk who had normal screening mammograms and (in dense breasts) normal screening ultrasound, in order to investigate the added cancer yield and accuracy of breast MRI in the average-risk screening situation. Methods: Between January 2005 and December 2010, 1387 women at average risk of breast cancer, i.e. without personal or family history of breast or ovarian cancer, or tissue diagnosis of proliferative changes or atypias underwent a total of 1705 annual breast MRI screening studies at our institution. Mean age was 54 years, range 42-71 years, median 56. All women had normal clinical breast examinations and normal (BI-RADS 1-2) digital screening mammograms performed in accordance with EU guidelines. In women with breast densites beyond ACR II additional high frequency (> 10 MHz) physician-performed breast ultrasound was performed and women were included only if this breast ultrasound was normal. Patients underwent bilateral DCE breast MRI at 1.5T using a 2D GE pulse sequence. MRI studies were interpreted by two experienced breast radiologist in consensus. All suspicious lesions detected by MRI alone were clarified by MR guided vacuum assisted breast biopsy. Results: A total of 54 MRIs were rated positive (MR-BI-RADS 4/5) (54/1705; 3.2%). Biopsies performed in these women were positive for breast cancer or DCIS in 18, and revealed high risk lesions in another 8 patients, yielding an additional cancer yield of 11/1000. In 28 women, biopsy revealed benign changes only. This translates into a PPV of 33% (18/54), or 48% (26/54) if high risk lesions are included. Of the 18 cancers, 11 (61%) were invasive and 7 (39%) DCIS. Mean size of invasive cancers was 11 mm (median 10, range 4 -22). Invasive cancers were intermediate or high grade in 9/11, DCIS in 6/7. All invasive cancers were staged pN0, M0. Minimal cancer rate was 13/18 (72%). Distribution of mammographic breast densities in women with MRI-diagnosed cancer was as follows: ACR I in 2 (11%), ACR II in 3 (17%), ACR III in 8 (44%), ACR IV in 5 (28%). This was equivalent to the distribution of breast densities in the entire cohort. Conclusions: In this cohort of heavily pre-screened women at average risk, the additional cancer yield achieved through MRI was high (11/1000). Although the biologic profile of MRI-only detected additional cancers was indicative of prognostically relevant disease, with a high proportion of high-grade cancers, stage distribution of cancers was favorable. In experienced hands, the PPV of MRI screening in this average risk cohort was comparable to those of mammographic screening programs or to that of MRI high risk screening cohorts. Mammographic breast density did not predict the likelihood with which additional cancers were identified through MRI. In women with dense breasts who underwent screening US in addition to mammography, there is still a significant reservoir of undetected cancers. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr S1-09.