Updated Breast Cancer Guidelines for HER2 Testing

A new update to clinical practice guidelines for HER2 testing in breast cancer was published online last week by the American Society of Clinical Oncology and the College of American Pathologists in the Journal of Clinical Oncology. The guidelines recommend that all women with invasive breast cancer (primary or recurrence) are tested for HER2 status—a practice already being implemented across the United States. It also outlines details of sample preparation and HER2 testing, which can be carried out by two different platforms: immunohistochemistry to measure protein expression, or in situ hybridization to measure gene amplification. Although for the majority of cases, testing will give a clear answer, showing either HER2-positive or HER2-negative status, approximately 5% of cases or less will test equivocal. In these cases, the test should be repeated, but using the other testing. “It’s important to apply context,” says lead author Antonio Wolff, MD, professor of oncology at the Johns Hopkins Sidney Kimmel Comprehensive Cancer Center in Baltimore, in an interview with Medscape. For example, if a tumor is low grade, measures of proliferation are low, and ER testing is positive, all of which might suggest a less aggressive tumor type, but if the HER2 test comes back positive, then he suggests a double-check. “I would want some reassurance from the pathologist on the test result.” Dr. Wolff also suggested that it is worth retesting if the clinical course of the disease is surprising. For example, he hypothesized about a case in which other pathological features point to a low-grade tumor, and the HER2 test in the original primary tumor came back negative, but then the patient...