‘Arbitrary’ Standards Used in Lab Tests for Breast Cancer

"Arbitrary standards" used to determine the outcome of a test performed on breast cancer patients could lead some women to miss treatment to prevent recurrence of the disease, according to a new study from Baylor College of Medicine, the Washington Post reports. Each year, about 200,000 breast cancer patients undergo a test that measures the "estrogen receptor status" of tumors. About 70% of breast cancers are "estrogen-receptor positive," meaning that the cancer cells have estrogen receptors and the patients can be treated with the drug tamoxifen, which minimizes the chances of recurrence. Women whose tumors do not have the receptors do not benefit from tamoxifen, however, so "doctors generally do not prescribe the drug for them," the Post reports. Over the last decade, laboratories have developed a new technique for conducting the receptor test, but many labs use "arbitrary cutoffs" for determining whether test results are positive or negative. The study revealed that although pathologists may classify test results as positive if as few as 1% of tumor cells show a color change, many medical laboratories require 10% to 20% of cells to show a change before giving a positive result. D. Craig Allred, a professor of pathology at Baylor, predicted that if most U.S. laboratories use a 10% cutoff for judging a test to be positive, about 5% of breast cancer patients -- about 10,000 patients a year -- will be misclassified as estrogen-re