More factors to consider about the uses of MRI in breast cancer screening and treatment
The controversial issues surrounding the use of MRI for breast cancer screening purposes have been discussed at length, but may be summarized in four basic points.
- Firstly, MRI is seen as being too sensitive, leading to many false positive results.
- Secondly, MRI lacks specificity. It rarely identifies a potential lesion with enough specificity to actually do something about it without requiring additional imaging or biopsy.
- Thirdly, the lesions found are often very small and deep, requiring an MRI guided biopsy.
- Finally, MR is a very costly exam.
MRI diagnoses more lesions, but does it detect significant disease?
One of the problems with MRI breast cancer screening use, is that suspicious or unusual findings are seen at a much higher rate than with mammography. Often MRI will detect additional ‘foci‘ of contrast enhancement other than the main lesion in question. In fact this occurs about 30% of the time. As a result of these new findings, the treatment plan is altered in about 11% of patients.
There is no question that in some cases, MRI is able to detect a potential breast cancer threat very early and the interventions are warranted. But in many instances MRI detects secondary lesions which turn out in the end to be completely benign. There is a real danger that MRI screening leads to a more aggressive treatment than was really necessary.
There really is no consensus on what would constitute a significant disease discovered through MRI. Often, MRI detects subclinical diseases that would never have been clinically relevant. Also, MRI quite often detects breast cancer that is currently being treated adequately with systemic breast cancer therapies or radiation therapy.
Common MRI false positive findings
False positive findings is a real problem with MRI breast cancer screening. MRI is very good, or very sensitive, at detecting unusual breast developments, but is not at all recommended as a test to differentiate benign from malignant breast tumors. So, as a consequence, a percutaneous biopsy of all potentially suspicious breast lesions in required following the initial MRI screening. Common benign MRI false positive findings include duct hyperplasia, papilloma, sclerosing adenosis, fibrocystic breast changes, adenofibroma, lobular carcinoma in situ, ductal atypica, and simply normal breast tissue at different times in the menstrual cycle.
Lack of specificity with MR
The specificity of MRI in terms of breast cancer screening generally ranges between 37% to 97%. That is an overall figure, but points to the high likelihood of additional imaging or biopsy studies that will be required following a positive MRI scan. Another thing to consider is that the interpretation criteria of MRI is quite inconsistent, and invites a wide range of interpretation.
MR guided biopsy
If a lesion detected by MRI is not also seen by mammography or ultrasound, then some kind of system for needle localization or biopsy is required. This is one of the most important clinical applications of breast MRI. However, an MR guided biopsy procedure is very time consuming, taking on average between 45 minutes to just under two hours. There are limitations to the procedure as well. Usually one only has access to the lateral side of the breast. Also, the patient has to be moved alternately in and out of the closed magnet. Once the lesion is removed, it is not possible to confirm this removal with MRI after the surgery. There can also be artifacts of the needles on gradient echo images.
Cost limitations for MRI in breast cancer screening
MRI exams are considerably more expensive than mammography or ultrasound. Also, MRI is used in just about every health application within the hospital setting. It is difficult to schedule time on the equipment just for breast cancer imaging.
Conclusions about the use of breast MRI in cancer screening
So, in conclusion is must be stated that the use of MRI in breast cancer screening must be approached with discernment. It is emerging as a promising adjunctive tool for breast cancer detection, but cannot be used as an alternative to percutaneous biopsy at the present time. On the plus side, MRI has been shown to be a promising adjunctive tool in detecting both invasive breast carcinoma and DCIS. But because of its lower specificity, MRI cannot be used as an alternative to percutaneous biopsy in differentiating benign from malignant lesions.
The best advice at present is to use breast MRI selectively to help detect breast cancer when conventional imaging is limited or questionable. In these situations, MRI can frequently give valuable information, which may change the course of treatment and hopefully without generating an unacceptably high false-positive biopsy rate.
Here are some common Q&A on MRI factors…
- What are the factors of the relative signal intensity (brightness) of the tissues in an MRI image? The radio frequency pulse and gradient waveforms used to obtain the image, intrinsic T1 and T2 characteristics of different tissues, and the proton density of different tissues.
- How is MRI useful? MRI is preferred to CT when soft tissue contrast resolution must be highly detailed. It is also useful for vascular imaging, hepatic and biliary tract abnormalities, masses in the female reproductive organs, certain fractures, and bone marrow infiltration and bone metastases.
- What are some disadvantages of MRI? It is relatively expensive, and requires longer imaging times than CT and may not be immediately available in all areas. Other disadvantages include the magnetic field, patient claustrophobia, and contrast reactions.
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