22nd June 2019, Dr Chee L Khoo
Screening mammography has been shown in many prospective, randomised, clinical trials to reduce breast cancer deaths by between 25-40% (1-4). Unfortunately, small but high-grade cancers can be masked by the presence of dense breast tissues or may be confused as benign breast disease in mammograms. In fact, in countries that have national breast screening mammography programs, advanced breast cancers have not decreased (5,6). There are controversial arguments that screening mammograms have led to over diagnosis of small in situ or oestrogen receptor positive, indolent invasive cancers while it fails to detect the more aggressive, hormone negative and fast-growing ones (7).
Adding supplementary imaging modalities like ultrasound or breast tomograms can increase cancer detection in women with dense breasts. Breast ultrasounds when added to screening mammograms detects an additional 3.7 cancers per 1000 patients screened (8,9). However, like with all investigations, the positive predictive value of ultrasound is much lower than mammography resulting in higher levels of biopsies being performed on benign lesions.
Digital breast tomosynthesis (DBT) detects 1.2 additional cancers per 1000 patients screened (10) but produces many more images for the radiologist to inspect and increases the time required for interpretation. More importantly, breast tomosynthesis may not improve on the detection of significant lesions in dense breasts.
Dynamic contrast enhanced breast magnetic resonance imaging (DCE-MRI) is the most sensitive imaging method for breast cancer detection. Breast MRI to superior to mammography and ultrasound in identifying breast cancer at a significantly earlier stage in high-risk screening populations (11-13). Furthermore, the sensitivity of MRI in detecting these additional cancers is unaffected by the age of the patient, their breast density, or their genetic mutation status (23).
Magnetic resonance imaging-detected breast cancers have the advantage of being less frequently associated with axillary nodal metastases (21.4%) when compared with mammography detected cancers (54.6% p<0.001) (11) suggesting that breast MRI picks things up earlier than the other modalities. The American College of Radiology (ACR) and the American Cancer Society (ACS) currently recommend intensive imaging screening with DCE-MRI for women with BRCA 1 and BRCA 2 mutations or women at a greater than 20% lifetime risk for the development of breast cancer using computer-based risk assessment models (25, 26). We reviewed the role of breast MRI in breast cancer screening a few months ago here.
DCE-MRI can be costly, involved long scan time and can be claustrophobic for many. Thus, it is of limited use in population-based screening. Here is where abbreviated breast MRI (AB-MRI) comes in. DCE-MRI must contain a minimal number of MRI sequences that is necessary to detect enhancing lesions. What if we cut down the number of sequences but yet have enough accuracy to detect small early cancers? That’s what AB-MRI is – less number of sequences but yet enough to detect small lesions.
Kuhl et al compared DCE-MRI with AB-MRI and found the specificity and positive predictive value of AB-MRI is equivalent to that of DCE- MRI (94.3% versus 93.9% and 24.8% versus 23.4%) (14). The negative predictive value of the AB-MRI was 99.8%. AB-MRI takes less than 10 mins to acquire the required images versus 17 minutes for DCE-MRI with a reading time of 30 seconds for AB-=MRI.
Choi et al (15) recently reported a study using AB-MRI screening in women with a personal history of breast cancer but with no evidence of malignancy with previously performed mammography or ultrasound. The sensitivity of the AB-MRI was 100% and the specificity was 89.2%.
What about women with average risk of breast cancer?
In a study of AB-MRI in a cohort of women at average risk for the development of breast cancer, with no evidence of cancer with traditional screening methods, Kuhl et al. (16) found an expectedly high cancer detection rate of 15.1 per 1000 women screened. Like the cancers detected in high risk women, the majority were small, T1 invasive cancers, less than 1.0 cm in size, and over 90% were node negative.
Given its superior performance and the greatly reduced scan times resulting from the use of abbreviated protocols, AB-MRI has the potential to replace mammography as a stand-alone imaging tool for the detection of breast cancer, not only in high risk women, but in women of average or mildly elevated risk, such as women with dense breast tissue or a personal history of breast cancer.
AB-MRI or DCE-MRI is not for all women coming for screening. The EA1141 Trial is a prospective multicentre trial comparing AB-MRI with DBT in breast cancer screening in women with dense breasts. Recruitment has completed and is expected to report within the next year.
AB-MRI is now available at Spectrum Medical Imaging. They have a team of 5 dedicated breast radiologists offering their expertise and experience in AB-MRI to some of our patients. Have a look at what they can offer and the images previewed this week here.
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