HER2 is a gene and protein that helps normal breast cells grow and repair. But if cancer cells have too many copies of this gene or overexpress (overlay) the HER2 protein, they can grow and spread faster than normal.

About one in five invasive breast cancers are HER2 positive. Understanding how this information affects your diagnosis can help you choose the best treatment options.

Symptoms

Cancer can affect your body in different ways. Breast cancer is not an exception. Breast cancer symptoms can be anything from a hard, rubbery lump you feel in your breast to a node found by a doctor during an examination or mammogram.

When a biopsy of cancerous breast tissue shows high levels of the human epidermal growth factor receptor 2 protein (HER2), it’s said to be HER2-positive. This is an important finding, as it allows doctors to determine the best treatment for the patient.

HER2 promotes cell reproduction and growth. Breast cancer with too much HER2 can grow and spread faster than breast cancer with normal levels. The HER2 status of the patient, along with tumor grade and stage, can help determine what treatment is best.

The doctors test a tumor sample using immunohistochemistry to determine if it is HER2-positive. Doctors will use antibodies to search for HER2 on the surface of cancer cells. A test called fluorescent In Situ Hybridization (FISH) is sometimes used. These tests for extra copies of the HER2 gene can be helpful if IHC results need clarification.

Diagnosis

Most breast cancers are diagnosed with a biopsy, which obtains a tumor tissue sample to test for cancer cells. The biopsy is typically done after a lump or other abnormal breast area is felt and examined by your doctor. In addition to looking for cancer cells, doctors can also test the biopsy sample for HER2 proteins.

HER2 is a protein that helps cells grow and divide. Mutations in the HER2 gene trigger cancer cells to make too much of this protein, causing cancer to grow faster and spread (metastasize). Between 15 and 20 percent of all breast cancers are HER2-positive.

When HER2-positive breast cancer is diagnosed, the Abramson Cancer Center uses targeted therapy to help keep the cancer cells from growing and spreading. These therapies work by blocking HER2 receptors that fuel cancer growth.

Usually, a doctor will test a tumor sample for HER2 before recommending treatment. An immunohistochemistry test is done with a special staining process that scores the number of HER2 proteins on the tumor cells. A score of zero or one means the tumor is HER2-negative; a score of 2 is borderline; and a score of 3 indicates the cancer is HER2-positive.

Doctors can also use fluorescence in situ hybridization to see if HER2 is overexpressed in the tumor cell. If the results from HER2 testing need to be clarified, a doctor may want to retest using different techniques or another type of test.

Treatment

The survival rate of HER2-positive cancer is higher than other breast cancers. However, advances in treatment are improving the long-term survival rate. This cancer type is treated using chemotherapy and targeted therapies that attack the HER2 tumor cells. These treatments reduce the size of the tumor and the chance of recurrence.

The HER2 test can be performed on cancer tissue samples from a surgically removed tumor or a biopsy. The test can be performed using antibodies that look for HER2 on the surface of cancer cells. IHC tests are graded as 0, 1, or 2 (two is borderline). The HER2 test can be used in conjunction with FISH tests.

Doctors can recommend other diagnostic tests, such as MRI or CT, to determine if the cancer has spread. They may suggest a clinical study that offers treatment options not available to the public. They may also tell a clinical trial that includes therapy options unavailable to the general public.

HER2-positive breast cancer can occur in stages 0 through 5, but doctors are most concerned about HER2-positive breast cancer that has spread or metastasized to other organs in the body. Advances in testing mean that HER2-positive cancer can be distinguished from hormone-sensitive breast cancer, which tends to grow and spread more slowly.

Prevention

Breast cancers identified as HER2-positive grow faster and are more likely to spread (metastasize) or return after treatment (recur). They also respond better to treatments that target the HER2 protein. Researchers have learned a great deal about how the HER2 gene and protein work, which has helped improve survival statistics for people with HER2-positive breast cancer.

About 1 in 5 invasive breast cancers are HER2-positive. The cancer cells have extra HER2 protein receptors on their surface. When the gene that makes HER2 has mutations or additional copies, these different receptors make breast cells grow and multiply uncontrollably. Bladder cancer, gastrointestinal cancer and ovarian cancer can also be HER2-positive.

When doctors diagnose breast cancer, they will test for HER2 status. This is done with a tissue sample from a biopsy or surgical procedure. The HER2 status of the tumor tells doctors how to treat it.

The HER2 test is usually one of the first tests doctors perform. This test, a mammogram and a physical exam help them decide whether or not to order a biopsy. The results of the HER2 test are usually available within one to three weeks. If a woman has HER2-positive cancer, her doctor will likely recommend chemotherapy and surgery. This is because HER2-positive breast cancer tends to be more aggressive and is more likely to spread than hormone-sensitive or ER-PR-positive breast cancer.