Magnetic Resonance Imaging Mri - Screening For Cancer: Breast Cancer

Content provided by the Faculty of the Harvard Medical School

Magnetic resonance imaging (MRI)

A breast MRI is a high-resolution way of visualizing the breast without radiation. It is useful when a doctor suspects there is a tumor that is not showing up during a physical exam or mammography. It may also be used to determine the size and extent of a known tumor.

Breast MRI can be used in addition to mammography or ultrasound. Doctors use MRI when they suspect the presence of an "occult" breast cancer. This is when a woman has a swollen underarm lymph node that is found, by aspiration or biopsy, to contain cancer cells, yet no sign of cancer appears on a breast exam and mammogram. In most such patients, breast MRI can identify the site of the cancer if that particular cancer originated from the breast. MRI can also be used to examine the chest wall or pectoral muscles for suspected cancer, as these areas are hard to reach with mammography. As discussed below, breast MRI is useful in patients who have a genetic predisposition to breast cancer development or a strong family history.

Another feature of breast MRI is its ability to detect hidden second cancers in the breast of a woman who has already been diagnosed with one cancer. In some cases, the detection of a second cancer in the same breast may alter treatment approaches in selecting lumpectomy and radiation therapy (in the case of a single breast cancer) versus mastectomy (if more than one cancer is found in the breast).

A potential downside to using breast MRI is its ability to detect lesions that are not cancerous, but are suspicious enough to require a surgical biopsy procedure. Additional roles of breast MRI that are under evaluation include its use in detecting cancers in the opposite breast of a patient with one breast cancer already diagnosed.

Doctors also use breast MRI to determine the size and extent of a known tumor in a breast cancer patient. This is especially useful if the cancer is difficult to measure by mammography, as can be the case with an infiltrating lobular cancer. If you are taking anticancer drugs to shrink a tumor before surgery (a process called neoadjuvant therapy), MRI can help reveal whether the tumor is responding to the medication. In addition, MRI may be used to check for recurrences after lumpectomy.

Breast MRI requires special equipment designed specifically for breasts. To have an MRI, you lie very still within a large machine, face down, with your breasts suspended into a cushioned, bra-like holder. Your face and head are near the open ends of the magnet chamber. During the procedure, a dye is injected into your arm. Short bursts of high-frequency waves stimulate hydrogen atoms in cells to emit signals that are collected and turned into an image by a computer. The image is made in 5-10 sequences, each of which is 3-5 minutes long, with breaks in between. The entire examination takes about 45 minutes. The MRI machine makes loud clanking sounds. Ask for ear plugs.

MRI is expensive and somewhat technically difficult. It requires a specialized machine and radiologists experienced in its use. Nevertheless, major medical centers are finding that breast MRI, used in conjunction with mammography and ultrasound, can be a powerful tool for some patients.

This imaging method has some limitations, however. It can produce false positive readings in which a benign abnormality might resemble a cancer. Another drawback is that MRI is able to identify DCIS in only 50% of patients. Because of these problems, MRI is not recommended for routine screening of women at low or average risk of breast cancer. However, some breast centers use MRI and mammography to screen women who are at very high risk of breast cancer because they carry a mutation of BRCA1 or BRCA2. MRI tends to be more sensitive than mammogram in women with these genetic mutations. Women in this group may require an annual MRI as well as an annual mammogram, plus a clinical breast exam every six months.

Last updated:	April 23, 2007