HER2-positive breast cancers can be treated with drugs that target HER2, called targeted therapies. These drugs may be given alone or with chemotherapy. Most doctors recommend testing for HER2 status in every patient with early-stage or metastatic breast cancer. The results significantly impact treatment recommendations and choices.
The stage of your breast cancer (whether it has spread beyond the primary tumor site and into nearby tissue or organs, including the lymph nodes) is essential because it helps determine which treatment options are available.
Your outlook is better if your cancer is at an early stage when it is first diagnosed. HER2-positive breast cancer patients status is determined by testing the levels of a protein called HER2 in your tumor or biopsy sample. The HER2 gene normally regulates cell growth, but a mutation or overexpression of the HER2 protein can cause breast cells to grow faster and form a tumor.
A test called immunohistochemistry (IHC) is usually done first to measure HER2 levels in your tumor. The test gives a number from zero to three, with two being a borderline diagnosis and three being HER2 positive. If the IHC results aren’t precise, your doctor may order a fluorescence in situ hybridization (FISH) test.
HER2-positive breast cancer is generally treated with chemotherapy and other drugs targeting the HER2 protein. These targeted therapies have dramatically improved survival rates for people with this aggressive breast cancer subtype. People with HER2-positive breast cancer who receive neoadjuvant (before surgery) chemotherapy and adjuvant therapy with trastuzumab have the best outcomes.
If breast cancer is HER2 positive, it will likely be treated with drugs that target the HER2 protein. These targeted therapies don’t harm normal cells and can kill cancer cells with fewer side effects than standard chemotherapy.
HER2 results can also help doctors decide whether to use hormone therapy. Hormone therapy works by blocking the estrogen and progesterone receptors in the tumor to stop them from stimulating growth. But not all breast cancers are sensitive to estrogen and progesterone.
Some breast cancers have low levels of these receptors or no estrogen or progesterone receptors. These are called estrogen receptor-negative (ER-negative) or triple-negative breast cancers. They’re less likely to respond to hormone therapy.
Scientists discovered the HER2 gene in the 1980s and found that specific mutations in this gene can cause abnormal cell growth and cancer formation. Cancers that overexpress the HER2 protein grow faster and are more challenging to treat than those that don’t.
Your doctor will biopsy a small piece of your tumor to determine its HER2 status. If your HER2 test result is equivocal, your doctor may order a different tissue sample or other tests, such as FISH, to clarify. If your cancer recurs or spreads, getting a new biopsy to re-test for HER2 and hormone receptor status is essential.
When a cancer cell is HER2-positive, it has too much of the HER2 protein. This protein typically tells breast cells when to grow and when to stop growing, but when the gene that makes HER2 goes awry, breast cancer cells grow out of control.
HER2-positive cancers are more likely to spread or metastasize to other body parts, such as the brain, lungs, and bladder. Generally, when a patient’s cancer is both HER2-positive and hormone receptor-positive (ER+/PR+), it has an even worse prognosis than HER2-positive cancers that are ER-positive but not PR-positive.
After endocrine therapy and targeted treatments, patients with HER2 and ER+/PR-positive breast cancer have more difficulty getting their tumors into remission. Overall breast cancer survival rates are based on the stage of your cancer at diagnosis and other factors, such as nodal status.
Cancer’s stage refers to how far it has spread at diagnosis and can be measured using imaging tests. A biopsy of a sample of the cancerous tissue can also determine it.
Hormone Receptor Status
The hormone receptor status of your tumor relates to how it grows and spreads. This information is essential because HER2-targeted therapies, including Herceptin, significantly improve survival rates for HER2-positive cancers when combined with other treatment options.
HER2 status also influences which chemotherapy drugs are most effective for you. When researchers first found that the HER2 gene and protein are linked to breast cancer growth, they realized that finding ways to target these receptors could improve patient outcomes.
Their foundational studies helped define HER2-positive breast cancer as a distinct disease and opened the door for years of research leading to successful treatments. The HER2 status of your breast cancer is determined through a pathology test known as immunohistochemistry (IHC).
An IHC score of zero or one indicates that the cells don’t have HER2 on their surface. A score of two or higher indicates that the cells do have HER2. If you have an IHC score of two, you may need additional testing called FISH. This pathology test looks at the genes that encode HER2 to determine whether there is more than one copy of the gene, which is called amplification.