How Do You Tell Whether a Breast Cancer is HER2 Positive? Ongoing Studies Keep Debate in High Gear

Extract

More than a decade after the drug trastuzumab (Herceptin) won approval in 1998, scientists still disagree over how to identify breast cancer patients for treatment. Trastuzumab targets human HER2, which contributes to poor outcomes in breast cancer when amplified. HER2-positive cases account for up to 20% of all newly diagnosed breast cancers, and there is no argument about trastuzumab's efficacy in these cases.

The debate is over the assays used to determine HER2 positivity: Which is more accurate? Even more controversial, how should their results be interpreted? Breast cancer strikes more than 200,000 women in the United States every year, so even small discordance rates between HER2 assays can mean thousands of potentially inaccurate findings. That's worrisome not just because women misclassified as false negative are denied trastuzumab but also because false-positive results needlessly saddle HER2-negative patients with the drug's $100,000 annual price tag—not to mention its side effects, which can include heart failure.