MRI (magnetic resonance imaging) is sometimes used as a screening test for breast cancer, especially in young, premenopausal women who have higher-than-average risk of breast cancer. MRI accuracy can be affected by hormone levels, which naturally go up and down each month during the menstrual cycle. For women who have regular menstrual cycles, the first half the cycle -- when progesterone levels are lower -- is usually the best time to do a breast MRI. For women who have irregular menstrual cycles, figuring out the best time to do breast MRI can be more difficult.
A very small study found that measuring progesterone levels before breast MRI in premenopausal women with irregular menstrual cycles can help better time the MRI, improving the test's accuracy and reducing the likelihood of repeat tests.
Breast MRI is expensive and not recommended as a routine screening tool for all women. Still, it can be recommended for screening women at high risk because of strong family history or an abnormal breast cancer gene (BRCA1 or BRCA2). Breast MRI is not a perfect tool. It's considered more sensitive than mammography in identifying breast cancer, but MRI also can miss some cancers that mammography would detect. That's why breast MRI is recommended only in combination with other tests, such as mammogram or ultrasound.
MRI uses magnets and radio waves to produce detailed three-dimensional images of the breast. To better identify an abnormal area, a contrast solution (called gadolinium) usually is injected through an IV line during the MRI. The contrast solution tends to collect in areas of cancer growth, showing up as white areas on the dark background of the MRI image. This helps the radiologist see which areas might be cancer.
When progesterone levels in the body are high there is more blood flow in the breast and the contrast solution tends to collect throughout the breast. This makes it harder to distinguish between abnormal and normal tissue, which makes it more likely that the MRI will have to be done again.
In this study, 11 premenopausal women with irregular menstrual cycles were having breast MRI as part of their overall breast cancer screening plan. Instead of using the women's menstrual history to schedule the MRI, the researchers measured the women's progesterone levels with one or more blood tests.
Breast MRI wasn't done unless the progesterone level was below a certain amount. If the progesterone level was high, the blood test was repeated until the progesterone level was below the specified level for an MRI:
- eight women needed only one blood test
- two women needed two tests
- one woman needed three tests
With this approach, none of the women needed to have a repeat MRI. There is some cost and inconvenience associated with the blood tests, but the researchers said that the benefits of avoiding an expensive second MRI outweighed the cost and inconvenience of the blood tests.
Measuring progesterone levels to figure out the best time for breast MRI isn't done routinely right now, but may make sense, particularly for women with irregular menstrual cycles. Still, the timing of any breast MRI should take into consideration where each woman is in her menstrual cycle. Unfortunately, this usually isn't done, which means avoidable second breast MRIs are done.
If you're premenopausal and breast MRI is part of your breast cancer screening plan, talk to your doctor about timing your MRI with your menstrual cycle. You may want to avoid scheduling the MRI during the second half of your cycle when progesterone levels are higher and the risk of needing a repeat MRI is greater. If your cycle is irregular, you may want to ask your doctor if measuring your progesterone levels to schedule the MRI makes sense for you.