Kenneth J. Bloom, MD, Chief Medical Officer, Clarient, discusses retesting patients who present with HER2-positive characteristics but receive HER2-negative test results.

Bloom's first choice for HER2 testing for patients with breast cancer is immunohistochemistry (IHC). If the initial test says the tumor is HER2-negative and the patient has characteristics that do not suggest HER2 positivity, such as a low tumor grade, strong progesterone receptor expression, and a low proliferation index, then a second test is not needed.

If the test returns negative and a single positive characteristic is present a second test should be performed. The question that lingers is whether the second test should be performed on the same or a different tissue block. Breast cancer heterogeneity allows for some blocks to test differently than others.

The second test should use a different assay than the first. The test you use first can vary, but Bloom suggests IHC (View more on this topic >>> Dr. Bloom Compares HER2 Screening Assays).

Bloom notes that it is important to test using a second methodology because of the magnitude of improvement seen with the addition of Herceptin.