Breast cancer is among the leading causes of cancer death in women. Dense breasts are an independent risk factor of breast cancer. In women with dense breasts, there is higher glandular tissue and fibrous connective tissue and low fatty tissue. Screening mammography can detect about 98% of cancer in fatty breasts, but can more easily miss breast cancer in dense breasts, resulting in a negative mammogram and providing patients with a false sense of reassurance. Women with dense breasts may require supplemental screening to assist in cancer detection. Now, a new study has found that breast magnetic resonance imaging (MRI) is superior at detecting breast cancer in women with dense breasts as compared to common supplemental screening methods.

Hand-held breast ultrasound, automated breast ultrasound, digital breast tomosynthesis (DBT) and breast MRI are the four most common supplemental imaging tests. In a study to measure the most beneficial screening method for women with dense breasts, researchers at the University of Toronto (Ontario, Canada) conducted a meta-analysis on 22 studies that included 261,233 patients screened for breast cancer. Out of these, 10 studies covered hand-held breast ultrasound, four studies covered automated breast ultrasound, three studies covered breast MRI, and eight studies reported on DBT. Out of the patients included in the study, 132,166 had dense breasts and a negative mammogram.

Risk assessment models have been used to identify patients with an average and intermediate risk of developing breast cancer. In the United States, women with an estimated lifetime risk of 12 to 13% of developing breast cancer are considered average risk. Factors that elevate the risk to intermediate include having a history of treated breast cancer or previous breast biopsies with high-risk lesions. High-risk patients, with a lifetime risk of 20% or higher, were excluded from the study since the benefit of breast MRI is already established in high-risk populations.

A meta-analysis found that out of the 132,166 patients with dense breasts, 541 breast cancers that were initially missed on mammography were detected using supplemental screening methods. Breast MRI was the most superior screening method and could detect even the smallest of cancers. Excluding MRI, the analysis found no significant difference between the other supplemental screening methods. These results indicate the effectiveness of breast MRI in cancer detection, although more research is required.

“MRI is far superior in terms of cancer detection compared to hand-held ultrasound, automated ultrasound and digital breast tomosynthesis. Our results about the role of MRI in supplementary screening will allow stakeholders to guide healthcare policies in this setting and direct further research,” said study co-author Vivianne Freitas, M.D., M.Sc., assistant professor at the University of Toronto, Canada. “Before we can advocate for wider application of breast MRI in these women, further evaluation of cost-effectiveness of breast MRI compared to other techniques, effect on mortality reduction, etc., will need to be studied. At the current time, availability and cost of the breast MRI remain the biggest barrier for widespread implementation.” 

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