Breast Cancer Gene Test May Be Inaccurate

Mammograms showing a normal breast (left) and a cancerous breast (right).

A breast cancer gene test that is commonly used may be flawed in its ability to identify an important gene that determines which treatment a woman receives, according to new research.

The results a new study showed that the breast cancer gene test, called the Oncotype DX, resulted in several false-negatives for the HER2 gene. Usually, women who test positive for this particular gene receive Herceptin (trastuzumab) therapy in conjunction with other medications to lower their likelihood of recurrence.

According to Dr. David J. Dabbs, a professor and chief of pathology at Magee-Womens Hospital of the University of Pittsburgh Medical Center and lead author of the study, the false-negatives indicate that women could be receiving a treatment that is completely wrong for them.

However, Dr. Lori J. Goldstein of the Breast Evaluation Center at Fox Chase Cancer Center in Philadelphia says that the Oncotype DX was never designed to be a test for HER2.

"None of us would request Oncotype for the sole purpose of getting HER2… we're usually ordering it for other reasons and, as part of that test, we get HER2,” she said, as quoted by HealthDay, adding that oncotype has been known to be a reliable identifier of estrogen receptor-positive and progesterone-positive tumors.

"Anyone who has had this test performed needs to make sure that their hormone-receptor analyses were done by other FDA-approved methods and not rely upon this test alone," HealthDay quoted Dabbs as saying. The two valid tests for HER2 include immunohistochemistry (IHC) and fluorescent in situ hybridization (FISH), which are approved by the U.S. Food and Drug Administration (FDA).

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