SCREENING WITH MRI: Now, Later or Never???

OBJECTIVES:
MRI and mammography both take pictures of the breast, but in different ways. An MRI uses magnets that emit radio waves to produce a three-dimensional view of the breast and the underlying structures and vessels. Mammography uses low doses of radiation (x-rays) to produce a two-dimensional image of the breast. Is MRI ready to take a roll in screening? There are two studies out that lend a hopeful light in that direction.

• At Bonn University in Germany mammography and high-resolution breast MRI were offered to more than 7,000 women. From this group, 167 women had a confirmed diagnosis of DCIS. Researchers found that 93 (56%) of these lesions were visible on mammography and 153 (92%) lesions were found with MRI. Of the 89 lesions that were high-grade DCIS, 87 (98%) were found using MRI compared with 46 (52%) by mammography.
• A NEJM study, 969 women with unilateral breast cancer underwent a breast MRI in the contralateral breast soon after diagnosis. Although no abnormalities were found by clinical examination or mammography, MRI detected abnormalities in the unaffected breast in 121 patients (13%). In follow-up biopsies of women with positive MRI findings, 30 patients (25% of those receiving biopsies; about 3% of the total study group) were found to have invasive breast cancer.

WHAT’S NOW AND WHAT’S NEW?
Mammography is currently the standard method for diagnosing DCIS, which accounts for 20% of diagnosed breast cancers and is the earliest diagnosable stage. Left untreated, DCIS could progress over several years to a high-grade invasive breast cancer. At present MRI is used primarily for diagnostic purposes; evaluating augmented breasts, determining metastases or finding chest wall spread post-surgically. There is evidence that MRI may be used for screening. MRI may be considered as another option for screening women at high risk of developing breast cancer, but an MRI most likely will not be substituted for mammography. Women concerned about getting this test should be advised to talk with their physicians and find centers with experience in performing and interpreting breast MRI’s.

The new screening guidelines from the American Cancer Society recommend breast MRI and mammography yearly beginning at age 30 for women at high risk for breast cancer. This population includes women who meet at least one of these criteria:

• Known BRCA1 or BRCA2 gene mutation
• Strong family history of breast or ovarian cancer
• A 20% or greater lifetime risk of breast cancer (this can be calculated using a scientific tool that calculates a person's lifetime risk of developing breast cancer)
• Women who have received radiation therapy to the chest between the ages of 10 and 30
• Women with a first-degree relative with the BRCA1 or BRCA2 gene mutation who have not had testing themselves
• Women who have, or may have, a family history of a cancer syndrome that increases their risk of breast cancer

These ACS guidelines can be an appropriate resource for clinicians. The key is that technology is increasing our ability to detect and treat cancer when it is at its most curable stage. It is important, though, that the breast MRI facility has both experience in early detection and the capacity to perform follow-ups and biopsies.

WHAT ARE THE PROBLEMS?
Breast MRI may be a more sensitive test than mammography, especially when given with a contrast medium. The dye makes the cancerous area of the breast appear much brighter; however, it may also cause many areas of the breast that do not have cancer to appear abnormal. This causes an increased number of false-positive test results and thus may cause unnecessary biopsies and increased anxiety for many women.

Breast MRI cannot visualize calcifications (calcium deposits) and microcalcifications (irregular deposits of calcium) that typically surround DCIS lesions until or unless these abnormalities have developed vascularization. This usually occurs quite late in the cancer’s development. Mammography, on the other hand, can visualize calcium deposits early and accurately.

A positive finding on an MRI always requires a follow-up biopsy to confirm whether a suspicious finding is cancerous or a false positive. Many facilities are ill-equipped to perform biopsies with MRI guidance. Women may have to repeat MRI testing with a follow-up MRI-guided biopsy at another facility that is equipped to perform the procedure. A positive finding on a mammogram also requires a follow-up test; such as diagnostic mammography, ultrasound, and/or biopsy, but these tests are almost always readily available and do not require the specialized technology of an MRI-guided biopsy.

Obviously, breast MRI has limitations: It is about ten times as expensive as mammograms, a breast MRI costs anywhere from $800 to $2,000, compared with a mammogram, which costs anywhere from $85 to $150. The data supporting screening MRI is not nearly as strong as data supporting screening mammography. Breast MRI has not yet been well studied in women with an average risk for breast cancer and therefore should not be recommended for those women. Most clinicians recommend a mammogram every 12 months on women 40 years of age and older, but almost none will recommend breast MRI for screening. Breast MRI may be recommended for younger women at high risk for breast cancer. Some clinicians may allow for "reasonable and necessary" breast MRI on high risk younger patients.

Currently, no formal practice standards exist for breast MRI as they do for mammography. Training and accreditation (a process to determine if applicable standards are met) of MRI facilities is needed to ensure practice standards remain consistent from one facility to another. Currently breast MRI vastly differs in quality from center to center. Presently, there are no standards. Many poor-quality MRI’s are being done in those facilities that don't have adequate equipment, experience, or guidance. This can create a false reassurance in women who may actually have breast cancer or, alternatively, suspect cancers in women without cancer, leading to excessive, unnecessary biopsies and surgeries. New standards will definitely help address this concern.

CONCLUSIONS:
The use of MRI screening is supported for women with a very high risk of breast cancer. The next step is to adopt standards for performing and interpreting breast MRI, including the ability to biopsy lesions seen only on MRI. Once the quality of breast MRI is established, clinical trials can be implemented to determine whether screening MRI can improve survival without increasing the financial and psychological costs when compared with mammography.

Mammography is the standard method for diagnosing early breast cancers, which accounts for a proven 30% drop in cancer deaths with proper screening and follow-up. Although the early results of breast MRI studies are encouraging, breast MRI should not be substituted for mammography for women at average risk for breast cancer. However, it may be a valuable additional tool to screen for breast cancer in women at high risk for developing the disease.