MRI: An Exciting New Imaging Tool in Breast Cancer Diagnosis and Treatment Planning

by John Halloran, M.D.

Although MRI is not a new imaging tool, effective breast MRI for cancer detection has developed only over the last several years. For many years MRI has been used to evaluate breast implants for rupture and now is one of the most exciting and promising tools in the fight against breast cancer. There are two types of MRI scanners: “open MRI” and “high field MRI”. Open MR scanners have a more open design suited for patients who are claustrophobic. Another advantage of the “open MR” is that biopsies can be performed without having to remove the patient from the scanner. “High field” MR scanners have a short tunnel (called a gantry) and are similar in shape to a computed tomography (CT) scanner. MRI works by using a magnetic field.

Breast MRI examinations require the patient to have an intravenous (IV) catheter for administration of MRI contrast dye. Contrast is administered because it helps detect tumors. Many new, abnormal blood vessels form within tumors resulting in a much greater number of blood vessels in tumors than normal breast tissue. Consequently, more contrast dye localizes in the tumors than in the normal breast tissue making tumors appear “bright” and more easily identifiable on the MRI images. Some benign breast lesions may appear “bright” on MR images. Approximately one-third of lesions thought to be cancer on MR turn out to be benign lesions. Therefore, it is important to have the ability to perform MRI guided biopsies at the site performing breast MRI. This allows biopsy of tumors that may be evident only on MRI.

Advantages of MRI over mammography and CT include no radiation exposure and superior sensitivity in detection of subtle differences in the breast tissue. Disadvantages of MR include the cost and its limitation in distinguishing benign from malignant tumors.

Potential Uses of Breast MRI

• Screening patients with breast implants and/or “dense” breasts
• Breast cancer treatment planning: size and number of tumor(s)
• Problem solver
  

“Dense” breast tissue may obscure breast cancer on mammography. Breast implants limit visibility of breast tissue on mammography. MRI does not have these limitations.

The sensitivity of mammography in the detection of cancer in “dense” breasts is reported between 45% to 60% compared to 81% to 95% for MRI. The most exciting capability of breast MRI may be its ability to assist in decisions regarding breast cancer treatment. Effective surgical planning and treatment of breast cancer depends on accurate assessment of the extent of the cancer, the size of the tumor, and the presence of other cancer sites.

MRI clearly is better than mammography in identifying additional sites of tumor. Breast cancer frequently is present at more than one site at the time of diagnosis. These other tumors may occur adjacent to the known tumor or even in the opposite breast. Identification of more than one tumor ​may change cancer therapy. The presence of more than one tumor may result in higher rates of cancer recurrence and may be a contraindication to breast conservation surgery. A University of Pennsylvania study showed more than one-third of patients with breast cancer had more extensive disease depicted on MR compared to mammography and treatment planning was altered in more than one-third of these patients (based on the MRI information).

​MRI effectively screens for cancer in the opposite breast. In an American College of Radiology Imaging Network study, 9% of patients diagnosed with breast cancer had a cancer in the opposite breast as well. MRI is very effective in determining the size of breast tumors. It has been used to follow the response of cancer to chemotherapy and in deciding between mastectomy and breast conservation surgery after completion of chemotherapy.

Breast MRI can be a problem solver. It is used to evaluate patients with inadequately visualized or indeterminate lesions on mammography and patients with atypical findings e.g., negative mammogram and enlarged axillary (arm pit) lymph nodes. A study by the University of Pennsylvania and Mayo Clinic showed MR clearly defined all breast lesions that were poorly demonstrated on mammography. In addition, MR successfully identified 86% of breast malignancies in patients with axillary lymph node metastases with an unknown site of breast cancer (by mammography and physical exam findings).

Breast MRI is an exciting advancement in breast cancer evaluation. Its diagnostic capabilities are invaluable and these capabilities will continue to grow with the constant advances in MRI technology.


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