WHO SHOULD HAVE A SCREENING BREAST MRI?
MRI is the most sensitive technology currently available to detect breast cancer. However, in a situation akin to the proverbial million-dollar “hammer” where everything starts to look like a nail, there is a temptation to think of MRI as the solution to all breast diagnostic situations. The result is an epidemic of radiology reports that suggest a breast MRI “if clinically indicated” without reference to specific clinical guidelines.
Screening MRI works for high-risk women
Breast MRI has a defined role in the evaluation of high-risk women. When compared to mammograms and clinical breast exam, it can identify cancers that would otherwise be missed. In a sample of recent screening studies, MRI identified additional cancers after a negative mammogram in the contralateral breast (the breast without cancer on the other side) of 2.9 to 5.4% of women with primary breast cancer at the time of diagnosis. In studies where patients were followed with repeat MRIs over time, MRI detected breast cancer for 4% of women with history of chest radiation for treatment of other cancers (such as Hodgkin’s Disease), for 5.4% of women diagnosed with lobular carcinoma in situ, and for 1.1 to 1.4% of women with a genetic predisposition to breast cancer. In a separate study of high-risk women, mammograms found as many cancers as MRI, but the MRI found the cancers at a smaller size and earlier stage. [It is important to note that mammograms and MRI are complementary. In each of these studies, mammograms found cancers that were missed by MRI.]
Groups of women at high-risk
Based on these observations, several organizations* have published guidelines for use of screening breast MRI for high-risk women. The agreed high-risk groups for routine screening breast MRI include:
1. Women predisposed to breast cancer because they carry a deleterious mutation in the “breast cancer gene” BRCA 1 or 2
2. Women predisposed to breast cancer because they carry a deleterious mutation in another gene associated with several different types of cancer such as PTEN (Cowden’s Syndrome) or p53 (Li-Fraumeni Syndrome)
3. Women with an estimated lifetime risk of breast cancer of 20 % or more by a standard risk model based on family history such as the Gail Model, etc.
4. Women with previous radiation exposure of the breasts as with treatment of Hodgkin’s disease or monitoring tuberculosis or scoliosis (particularly if multiple x-rays were done during adolescence).
Some organizations also include:
5. Women with a previous biopsy showing lobular carcinoma in situ or atypical ductal or lobular hyperplasia, but this is often redundant since these conditions are frequently associated with a 20% lifetime risk in the Gail model above.
Screening breast MRI can be falsely positive and falsely negative
MRI has not been recommended for general screening because of the high false positive rate. Even in recent studies published in 2010 through 2012, MRI was reported as abnormal about five times more often than women actually had breast cancer. MRI also misses cancer: in the screening studies that reported all cancers – including those found between screening tests – about five percent of cancers were diagnosed in the interval after a negative MRI.
Should women with dense breasts have MRIs?
Recently, California Governor Jerry Brown signed a bill requiring radiologists, “…to include in the summary of the written [mammogram] report that is sent to the patient a prescribed notice on breast density.” The bill also states, “Nothing in this section shall be deemed to create a duty of care or other legal obligation beyond the duty to provide notice as set forth in this section.” This creates the uncertain situation where women will receive this information, but as yet, there is no good way to advise women on what to do about it.
One possibility is to do screening breast MRIs for these women because they have dense breasts on mammograms, but this is an untested option. In fact, I have found only one study reporting MRI in women with dense breasts, but in that study, all women had an additional factor – in addition to dense breasts on mammograms – that increased their risk, such as family history, etc. Even in the 612 women in this study who had factors in addition to dense breasts that increased their risk, 43 biopsies based on MRI alone were needed to find 9 cancers. If the other factors were not present, it is likely even more biopsies would have been needed to find this number of cancers which means that even more women would have had negative biopsies that did not help them. There is study underway in the Netherlands using breast density as a criteria for MRI screening, but there is no information from that study yet. Given the significant false-positive rate of screening breast MRI – and the real possibility of unreliable reassurance from a falsely negative study – this is an untested option.
This is a field with much active research, and we all hope for better answers as soon as possible. For the present, screening MRI should be used in accordance with guidelines offered by various professional organizations. All these guidelines are essentially the same and suggest screening MRI for women at high-risk. There is no consensus whether mammographically dense breasts meet this criteria for women who do not have other risk factors.
_______________________________
* Guidelines for screening breast MRI from various organizations:
American Society of Breast Surgeons
National Comprehensive Cancer Network You will need to create a log in for the NCCN Guidelines.