What does HER2-positive mean in breast cancer?

According to the National Cancer Institute's (NCI) Dictionary of Cancer Terms, HER2 is a protein involved in normal cell growth. "HER2 positive" describes cells that have a protein called HER2 on their surface, and in breast cancer this means the cancer cells have too much of it. The NCI states that in normal cells HER2 helps control cell growth, but cancer cells that make too much HER2 may grow more quickly and are more likely to spread to other parts of the body. Per the NCI, checking whether a cancer is HER2 positive may help plan treatment, which may include drugs that kill HER2-positive cancer cells. The NCI notes that cancers that may be HER2 positive include breast, bladder, pancreatic, ovarian, and stomach cancers. This is general information, not personal medical advice.

Last updated: 2026-07-12

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