MRI is more sensitive than mammography in high-risk women, but there is no proof of reduced mortality
There is no proof that an MRI improves long-term outcome for the majority of women with breast cancer, according to a study published recently in The Lancet. Compared with mammography, MRI screening of breast cancer for women with a known or suspected BRCA genetic mutation is more sensitive and equally specific, but survival data are not available to determine whether this translates into lower mortality.
While mammography is the most widely-used test for breast imaging, screening mammography does not visualise all cancers. The sensitivity of mammography is lower in women with dense breast tissue, and apparently localised cancer, as seen on mammogram, may prove to be extensive at surgery, and require mastectomy. The objective of this review was to evaluate whether use of MRI can improve outcomes of breast cancer screening and treatment, based on recent evidence.
In this review, which represents the first paper in The Lancet series on breast cancer, the authors conducted an electronic literature search of articles published from 1 May 2001 to 25 May 2011, in PubMed, Embase, and Cochrane. The strongest evidence of benefit for the use of MRI as a screening tool was found in women with BRCA mutations and in women with a family history of breast cancer. MRI has better sensitivity than mammography for the detection of invasive breast cancer, which results in the detection of smaller cancers and the occurrence of fewer interval cancers. However, none of the prospective randomised trials of screening with MRI – either in women in general or in women at high risk – had survival as an endpoint.
The researchers also found little evidence that MRI improves the short-term or long-term outcomes of breast-conserving surgery. They cite two randomised trials – MONET (MR mammography of non-palpable breast tumours) and COMICE (comparative effectiveness of MRI in breast cancer) that showed screening patients with MRI did not lead to any decrease in surgical procedures.
Key points
An electronic literature search between 1 May 2001 and 25 May 2011, identified pertinent clinical trials, retrospective studies, prospective studies, multicentre studies, meta-analyses and systematic reviews.
Uses of breast MRI include screening women at increased risk for breast cancer and guiding treatment regimens.
Compared with mammography, MRI screening of women with a known or suspected BRCA genetic mutation is more sensitive and equally specific in the detection of cancer, based on prospective studies.
For these women, as well as for those at high risk for breast cancer because of their family history, MRI detects smaller cancers, and there are fewer interval cancers than with mammography.
Additional studies are needed to determine whether MRI screening is useful in other high-risk groups, such as women with lobular carcinoma in situ or those at risk because of mantle irradiation.
American Cancer Society guidelines recommend annual MRI screening for women with a BRCA mutation, based on evidence from non-randomised screening trials and observational studies.
On the basis of expert consensus opinion, the American Cancer Society recommends against MRI screening for women at 15 per cent or lower lifetime risk for breast cancer.
Some breast cancers are detected only with MRI and not with other types of screening.
Two trials showed the increased sensitivity of MRI was not associated with better selection of surgical treatment or fewer surgeries.
Outcomes
Evidence to date is scanty for long-term outcomes such as rates of ipsilateral breast tumour recurrence and contralateral breast cancer incidence, but available data do not show a clear benefit for MRI.
In patients presenting with axillary nodal metastases but no detectable primary breast tumour, MRI can often identify the primary tumour.
Compared with other modalities, MRI is better for evaluating response to neo-adjuvant chemotherapy and residual disease after such therapy.
Very early changes in intracellular metabolism that are detectable by MR spectroscopy seem to predict response to treatment.
If this finding is confirmed in larger studies, use of this technique could avoid the toxicity and expense of continuing chemotherapy that will not benefit the patient.
Breast MRI before surgery in patients with known breast cancer has not been shown to improve the rate of negative margins or the need to convert from lumpectomy to mastectomy.
Compared with other modalities, MRI screening of breast cancer is better for evaluating response to neoadjuvant chemotherapy and residual disease after such therapy. Breast MRI before surgery in patients with known breast cancer has not been shown to improve the rate of negative margins or the need to convert from lumpectomy to mastectomy.