Yes, ERBB2 and HER2 are two names for the same thing. ERBB2 is the official name of the gene, while HER2 is the more common name used in clinical settings to describe the protein that gene produces. You’ll see both terms on lab reports, in research papers, and in conversations with oncologists, and they refer to the same biological target.
Why Two Names Exist
The confusion comes from the way genes and proteins get named by different research groups over time. The gene sitting on chromosome 17 has the official symbol ERBB2, short for “erb-b2 receptor tyrosine kinase 2.” That naming traces back to its discovery as part of a family of genes related to the epidermal growth factor receptor. The protein this gene produces, a receptor that sits on the surface of cells, became widely known as HER2 (human epidermal growth factor receptor 2). You may also see older references to “HER2/neu” or “c-erbB-2,” which are earlier aliases from the same discovery era.
In practice, doctors and patients almost always say “HER2.” Researchers and genetic testing labs more often use “ERBB2,” especially when discussing the DNA itself. A recent FDA approval for a lung cancer drug, for example, described its target as “HER2 (ERBB2)” in a single phrase, using both names interchangeably. When your pathology report says ERBB2 amplification, it means the same thing as HER2 overexpression at the gene level.
What This Gene and Protein Actually Do
The ERBB2 gene contains the instructions for building a protein receptor that spans the outer membrane of cells. This receptor acts like an antenna, picking up growth signals from the body and relaying them inside the cell to trigger division and survival. In healthy tissue, this process is tightly regulated. The receptor belongs to a family of four related receptors that work together in pairs to control how cells grow, divide, and repair themselves.
What makes HER2 unusual among its family members is that it doesn’t need to bind a specific signal molecule to become active. It’s essentially always ready to pair up with other receptors and start signaling. That feature becomes a problem when cancer cells make too many copies of it.
Gene Amplification and Protein Overexpression
In certain cancers, cells acquire extra copies of the ERBB2 gene, a process called gene amplification. Instead of the normal two copies (one from each parent), a cancer cell might carry dozens. Each extra copy churns out more HER2 protein, flooding the cell surface with receptors. More receptors means stronger and more constant growth signaling, which pushes the cell to divide rapidly and resist normal cell death.
This is why testing distinguishes between two related measurements. Gene amplification is assessed by looking at the DNA directly, counting how many copies of ERBB2 exist. Protein overexpression is measured by staining tissue samples and scoring how much HER2 protein appears on cell surfaces. The two results usually align: amplified genes produce excess protein. But the distinction matters for treatment decisions.
How HER2 Status Is Tested
Pathologists use two main methods to evaluate HER2 status. The first is immunohistochemistry (IHC), which stains a tissue sample to reveal how much HER2 protein coats the cell membranes. Results are scored on a scale from 0 to 3+. A score of 3+ means clearly visible, strong staining and is considered HER2-positive. A score of 0 means no detectable protein.
The second method, called FISH (fluorescence in situ hybridization), directly counts gene copies in the tumor cells. A ratio of HER2 gene copies to a reference marker of 2.0 or higher, combined with an average of 4.0 or more HER2 copies per cell, is the clearest positive result. FISH is typically used to resolve borderline IHC results scored at 2+.
A newer category called “HER2-low” has entered clinical discussion. This applies to tumors scoring IHC 1+ or IHC 2+ without gene amplification on FISH. These cancers were previously grouped with HER2-negative tumors, but newer antibody-drug conjugates have shown effectiveness against them, making the distinction clinically relevant. UK guidelines now recommend including HER2-low in pathology reports, though US and European guidelines have not yet formally adopted the term.
Cancers Where HER2 Status Matters
HER2 testing is most associated with breast cancer, where 15% to 20% of newly diagnosed cases are HER2-positive. Historically, HER2-positive breast cancer carried a worse prognosis because of its aggressive growth pattern. That changed dramatically with the development of targeted therapies.
But breast cancer isn’t the only context. Between 12% and 20% of gastric cancers are HER2-positive, and testing is now standard for advanced stomach and gastroesophageal junction cancers. ERBB2 mutations and amplification also play a role in certain lung cancers, as well as cancers of the colon, ovary, pancreas, and prostate, though testing in those cancers is less routine and more often tied to specific clinical trials or newer drug approvals.
Targeted Treatments for HER2-Positive Cancers
The identification of HER2 as a driver of cancer growth led to one of the earliest and most successful examples of targeted therapy. Trastuzumab, sold as Herceptin, is a monoclonal antibody that attaches directly to the HER2 protein on cancer cells, blocking its signaling and flagging the cell for destruction by the immune system. It transformed HER2-positive breast cancer from one of the most aggressive subtypes into one of the most treatable.
Since then, multiple additional therapies have been developed. These include other antibodies that target HER2 from different angles, small molecules that block the signaling activity of the receptor from inside the cell, and antibody-drug conjugates that deliver chemotherapy directly to HER2-expressing cells. The antibody-drug conjugate approach is what made HER2-low status relevant, since these drugs can find and attack cells with even modest amounts of HER2 on their surface.
The treatment landscape continues to expand beyond breast cancer. In 2025, the FDA approved a targeted pill for non-small cell lung cancer driven by ERBB2 mutations, reinforcing that HER2 and ERBB2 testing is becoming important across multiple cancer types, not just breast.