Exemestane

Of all the tests given to a woman newly diagnosed with breast cancer, one is crucial in determining her treatment plan. It measures the tumor's "hormone receptor status." If the tumor is estrogen or progesterone receptor positive that means her cancer's growth is dependent upon hormones; and a hormone-blocking drug, such as tamoxifen, will be prescribed for five years after her initial treatment. Unfortunately, many medical laboratories use arbitrary standards for determining test results, which in turn might inappropriately steer some women away from the most effective drug therapy.

To bring some order to the situation, a team of pathologists at Baylor College of Medicine, Houston, Texas has been working for years to improve hormone receptor testing standards. Along with colleagues at other medical centers, the Baylor team recently published a test-validation study (Modern Pathology, 7/04). It is the final step in a long process of defining the appropriate standards for a test that is given to at least 200,000 breast cancer patients each year in the U.S.

By way of background, pathologists have been measuring the hormone receptor status of breast tumors ever since the late 1970s. About ten years ago, doctors began to rely on a new hormone receptor test that is cheaper and easier to perform. The newer test called immunohistochemistry has been causing problems ever since, according to pathologist Syed K. Mohsin, MD, of the Breast Center at Baylor College of Medicine. Dr. Mohsin is the lead author of the newly published hormone receptor study.

In a telephone interview, Dr. Mohsin explained that there were only limited studies to tell doctors how well the newer test compares to the older method called biochemical assay. Additionally, the cutoff for determining a tumor's hormone receptor status--both for the old and the new test--was arbitrarily chosen to be 10% (i.e., a women tests positive only when 10% or more of the tumor's cells have hormone receptors).

"My colleague, Dr. Craig Allred, has been arguing for years that you can't use an arbitrary cutoff," Dr. Mohsin said, "Accuracy is crucial because the test will identify the patients who can benefit from the most effective form of therapy in breast cancer." In fact, he continued, the test can also determine a woman's treatment in the event of a recurrence or a metastasis (cancer spread to distant organs).

An earlier study conducted by the Baylor researchers in 1999 had led them to question the universally accepted, but arbitrary cutoff of 10%. "In our studies, we found that women with as little as 1% of tumor cells positive for estrogen or progesterone receptors can benefit from hormonal therapy [e.g., tamoxifen]," Dr. Mohsin said. His studies confirmed that, contrary to prevailing practice, women who fell into the range of 1% to 10% positive tumors cells for either hormone are candidates for hormonal treatment. Doctors who continue to use the old 10% cut-off risk misclassifying women and giving them a less effective treatment.

In the studies conducted by Dr. Mohsin and colleagues, the hormone receptor positive women had been treated with tamoxifen. Today, a woman may treated with one of the newer hormonal drugs, such as Zoladex (goserelin), Aromasin (exemestane), Arimidex (anastrozole), and Femara (letrozole). "If the tumor comes back," Dr. Mohsin said, "it's still possible that she will respond to one of these newer hormonal drugs based on the hormone receptor status of the primary tumor in the breast."

When to Have Yourself Retested

"The take-home message from our study is this: women should consider a second pathology opinion if the test shows the tumor is hormone receptor negative," he said. "The major problem in testing is the false negatives." That means that a woman is erroneously informed that her tumor is not dependent on hormones for growth. Odds are the tumor is--Dr. Mosin estimates that 75% of all women with breast cancer are hormone receptor positive. Women are also advised to ask what cutoff was used for their tests.

Typically, it is the oncologists who question the test results when they are hormone receptor negative, said Dr. Mohsin. "Physicians often send tissue to us at Baylor for a second pathology opinion. Many small labs produce erroneous results--in our experience, we see a 30% false negative rate." Even women treated years earlier can benefit from a second pathology, according to Dr. Mohsin, because hospitals usually keep tissue in paraffin for ten years. "So a woman can still have herself retested."

For More Information

-Visit the new Web site of the Breast Center, Baylor College of Medicine in Houston, Texas www.breastcenter.tmc.edu/cores/path

COPYRIGHT 2004 Center for Medical Consumers, Inc.
COPYRIGHT 2004 Gale Group