German investigators reported at the 2013 Breast Cancer Symposium in San Francisco that an abridged magnetic resonance imaging (MRI) protocol can accurately detect cancers among women whose mammographic screenings were negative.1 MRI, therefore, may reveal the type of tumor that mammography typically misses—and can do so in a time-efficient fashion, thus making MRI feasible for breast cancer screening, said Christiane K. Kuhl, MD, of RWTH Aachen University in Aachen, Germany.
“We already know that we find more cancers with MRI screening than with mammographic screening, including more invasive cancers and more ductal carcinoma in situ (DCIS),” she said.
These cancers may be more “prognostically relevant” than those detected by mammography, which can be “irrelevant,” she suggested. “The aim of new, nonmammographic screening strategies is not necessarily to detect more cancers but to improve the detection of cancers that are prognostically relevant.”
Types of Cancers Detected
Dr. Kuhl suggested that mammography has a “technology-inherent bias” for preferentially detecting slow-growing cancers. Detection is based on the identification of architectural distortions, spiculations, and calcifications, ie, pathophysiologic processes that reflect regressive changes such as hypoxia, necrosis, and fibrosis and that confer length-time bias, she said.
On the other hand, MRI detection of cancer is determined by the tumor’s angiogenic and protease activity, ie, by tissue alterations that directly correlate with carcinogenesis, cell proliferation, and metastatic growth, she maintained.
“MRI detection of cancers and DCIS is biased, therefore, toward biologically active, prognostically relevant disease. The MRI phenotype of cancers or DCIS reflects the disease’s ‘proteomic tool box’ for growth and metastasis,” she said.
Abridged MRI Modality
Current MRI protocols used for screening are identical to those used for diagnostic purposes and, as such, are time consuming to acquire and to read. Dr. Kuhl and colleagues, therefore, designed an abridged breast MRI protocol that would be more suitable for screening purposes. The MRI consists only of the first post–contrast-subtracted (FAST) images and their maximum intensity projection (MIP). The MIP images allow readers to quickly detect enhancement, while the FAST images provide further categorization of these enhancements, she explained.
They evaluated the screening MRI protocol in an observational study of 443 asymptomatic women at intermediate or slightly increased lifetime risk of breast cancer. All subjects had no abnormalities on digital mammography.
Experienced breast magnetic resonance radiologists rated the MIP images as positive or negative depending on the presence or absence of significant enhancement. They read the FAST images to provide Breast Imaging Reporting and Data System (BIRADS) scores and the full diagnostic MRI protocol to compare the abridged modality for diagnostic yield and accuracy.
MIP/FAST Screening
In 606 screening rounds, 11 breast cancers were detected, including 4 cases of DCIS and 7 invasive cancers, for a cancer yield of 18.3 per 1,000. All lesions were Tis or T1, N0, and M0; virtually all were grade 2/3, and the median tumor size was 8.4 mm. No interval cancers were diagnosed.
The sensitivity and negative predictive value of reading only the MIP image was already 98.9%; after reviewing the FAST images of the abridged protocol, it was 100%—equivalent to the full diagnostic protocol, Dr. Kuhl reported.
The MIP/FAST screening also compared favorably with mammographic screening with regard to the time needed to acquire or review images. The abridged protocol required 3 minutes of acquisition time (vs 21 minutes for the full protocol) and about 30 seconds of reading time.
The abridged MRI screening modality “allowed a substantial additional yield of biologically relevant invasive cancers and DCIS in this cohort of women at moderately or slightly increased risk of breast cancer,” Dr. Kuhl concluded.
“As long as so many women die of breast cancer, the search for improved screening strategies must continue. True screening breast MRI may be such a strategy,” she said. ■
Disclosure: Dr. Kuhl has served in a consultant or advisory role for Bayer.
Reference
1. Kuhl CK, Schrading S, Strobel K, et al: Accelerated breast MRI for breast cancer screening. 2013 Breast Cancer Symposium. Abstract 1. Presented September 7, 2013.
