What does HER2-positive mean?
Understanding HER2 status and targeted therapy
The short version
HER2-positive means the cancer cells have higher-than-normal amounts of a protein called HER2, which can help cancer cells grow. Targeted therapies exist specifically for HER2-positive cancers.
What HER2 is
is a protein that sits on the surface of breast cells and can help them grow. Some breast cancers have many more copies of the HER2 gene than usual, which leads the cells to make too much HER2 protein — this is called HER2-positive.
How HER2 is tested
HER2 is usually tested with a score of 0, 1+, 2+, or 3+ from an IHC test, sometimes followed by a FISH test to confirm. A score of 0 or 1+ is generally HER2-negative, 3+ is generally HER2-positive, and 2+ is considered borderline and usually needs the follow-up FISH test.
Go deeper: what "HER2-low" means
Some cancers once considered simply HER2-negative are now described as HER2-low (a 1+ or low 2+ result). This distinction is relatively recent and can affect eligibility for certain newer targeted therapies — it's worth asking your care team how it applies to your specific result.
Why it matters
HER2-positive cancers can often be treated with targeted therapies aimed specifically at HER2, in addition to other treatments your team may recommend.
Questions you may want to ask
What is my exact HER2 score, and what does it mean for me?
Am I a candidate for HER2-targeted therapy?
Will I need additional testing to confirm my HER2 status?