BOX 4-4
A Blood Test to Forego Mammography?

Imagine a blood test that could identify women whose risk of breast cancer is so low that they could safely forego regular mammogram screening. A recent study of post-menopausal women by Steven Cummings and colleagues suggests that such a test might someday be possible.19

Their study included more than 7,000 post-menopausal women whose average age was 66 years, and they found that the 4-year rate of breast cancer in women with undetectable serum estradiol levels was only 0.6 percent, compared to a rate of 3.0 percent for women whose estradiol levels were greater than 10 pmol/L (2.7 pg/mL), which translates into an approximately seven-fold difference between the two groups.

For comparison, the average 10-year risk for a 40-year old woman is approximately 1.5 percent, which is at or below the threshold for recommending regular mammograms. It is important to note, however, that Cummings’ study reported 4-year rates, and these cannot be assumed to be the same as 10-year rates. But the comparison remains impressive—and suggests that some women over 60 might have a lower risk of breast cancer than average-risk 40-year-old women.

It has been known for some time that the risk of developing breast cancer drops with declining levels of serum estradiol, which is the most active type of estrogen,37 but this study used a highly sensitive test to measure estradiol that allowed greater resolution of low estrogen levels than is possible in standard tests.

In fact, this is one of the caveats of the study. The minute quantities of estradiol that differentiate between high- and low-risk women required more expensive and sensitive tests than are currently available for clinical use. Assays used in daily clinical practice measure estradiol levels in the range of 10 to 20 pg/mL, and are not sensitive enough to distinguish levels between 0 and 10 pg/ml, whereas the average level of estradiol in the study was about 3 pg/mL.48

Another caveat is that because the study consisted of a 4-year follow-up period, breast cancer incidence might only be delayed to a later point in time in post-menopausal women with ultralow estradiol levels.

To date, there is no commercially available test. Research on the long-term accuracy and development of a clinically useful test will need to be completed before the test can be used to evaluate a woman’s risk of breast cancer.

Other potential uses of highly sensitive estradiol measurements might be to identify women whose risk profiles make them candidates for preventive treatments, such as anti-estrogen. Such a test would be a welcome addition to the mix of risk assessment tools.

are largely based on the fact that cancer incidence increases with age, but also because mammography is less sensitive in women younger than 40, because they tend to have dense breasts. More frequent mammography screening in younger women also has the downside of exposing a more radiation-sensitive breast to radiation, yet breast cancers in younger women tend to be more aggressive, suggesting younger women should be screened more often.

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