MRI (magnetic resonance imaging) is sometimes used as a screening test for breast cancer, especially in young, pre-menopausal 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.
The very small study reviewed here found that measuring progesterone levels before breast MRI in pre-menopausal 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 pre-menopausal 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:
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 pre-menopausal 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.
Measurement of serum progesterone concentrations can aid in scheduling breast MRI in premenopausal women who do not have regular menses, a small retrospective study found.
Of 11 women who had breast MRI when progesterone concentrations corresponded with the follicular phase of the menstrual cycle, none needed a repeat MRI, Richard L. Ellis, MD, of the Gundersen Lutheran Health System in La Crosse, Wis., reported in the December issue of the American Journal of Roentgenology.
The use of breast MRI has increased considerably during the past decade and is likely to increase further, evolving from an adjunct imaging modality to a primary screening tool for greater numbers of women, Ellis said.
But hormone fluctuations can affect gadolinium uptake in normal breast tissue, making interpretation of MRI findings difficult.
Previous research has shown that performing the scan during the follicular phase of the menstrual cycle -- days 3 to 14 in a normal cycle -- minimizes the tissue enhancement that results from these fluctuations.
Such timing works for women with regular 28-day cycles, but if women with irregular cycles or those who've had a hysterectomy but have normally functioning ovaries are scanned mistakenly during the luteal phase, false-positives could result because of gadolinium uptake in normal tissue or false-negatives because of masking of small enhancing cancers.
Many clinicians simply scan these women without regard to timing, and if the results suggest a false-positive result they rescan the patient two weeks later to determine whether the abnormal enhancement reflects hormonal fluctuation in normal tissue.
"In our experience, this practice resulted in many nondiagnostic examinations and repeat scans," Ellis wrote.
To see if progesterone levels could be used to successfully predict the timing of scans and thereby cut down on unnecessary MRI scans, he identified 135 women who had breast MRIs between February 2006 and July 2008 at his institution, and found that 11, ages 33 to 53, were pre-menopausal and had irregular cycles.
A serum progesterone concentration ≤1.5 ng/mL was considered to correlate with the follicular phase, and if the level was too high it was checked again three to five days later, and the test repeated until the concentration fell below the cutoff point.
Of the 11 patients, eight needed only one blood draw, two required two, and one required three to identify the follicular phase.
None of the MRI scans showed disproportionate enhancement of glandular tissue that would have required a repeat scan.
Repeat MRI scanning consumes time and resources, and can add considerably to the cost of care: Medicare reimbursement for bilateral breast MRI with contrast is $981.50 and reimbursement for serum progesterone is $29.15.
Therefore, it would require only one repeat MRI scan in 33 patients to be cost neutral, the author said.
The study sample was small, but because the science and endocrinology of menstruation are well understood, "large numbers of patients are not required to illustrate how progesterone concentrations can be used to help time breast MRI examinations in premenopausal women who lack a normal menstrual cycle."
These findings support the use of serum progesterone measurement to aid in timing of breast MRI in a select population, Ellis concluded.
The study was funded in part by Gundersen Lutheran Medical Foundation.
No disclosures were provided.
Primary source: American Journal of Roentgenology Source reference: Ellis R "Optimal timing of breast MRI examinations for premenopausal women who do not have a normal menstrual cycle" Am J Roentgenol 2009; 193: 1738-1740.
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