Understanding your pathology report is essential whether you’re new to breast cancer treatment or experiencing a recurrence. HER2 status determines whether your cancer cells will likely respond to medications that target HER2. HER2 testing is usually done with an IHC or FISH test.
Symptoms
A breast cancer diagnosis can be frightening, but it’s essential to know your symptoms so you can seek medical care as soon as possible. Breast cancer starts in the lining of the breast ducts or lobules and grows into a tumor, which can spread (metastasize) to other body parts. Most invasive breast cancers are HER2-positive, which means they overexpress the HER2 protein and grow more quickly than other types of breast cancer. If you have HER2+ status of breast cancer, treatment usually includes medicines that target the HER2 protein to slow or stop tumor growth. These medicines include monoclonal antibodies, antibody-drug conjugates, or kinase inhibitors, which block signals from the HER2 protein to other cells. Some of these treatments can cause serious side effects, including inflammatory reactions in the skin and liver. If you are pregnant or planning to become pregnant, you should not take these medicines because they may harm or kill the fetus. Your doctor will test your tumor for HER2 status with a biopsy sample from the original tumor or a new biopsy during follow-up.
Treatment
Whether you are in the early stages of diagnosis, undergoing treatment, or have already completed it, it’s essential to understand the different breast cancer treatments available and their impacts. A combination of factors — including where the cancer is, its size, and its hormone receptor and HER2 status — determines your specific treatment plan. A multidisciplinary team of doctors, nurses, and social workers will work together to create a treatment plan tailored to your needs. These treatments can be local, such as surgery and radiation, or systemic, such as chemotherapy or hormone therapy. Your team may recommend a clinical trial, an experimental treatment that offers more options than standard treatments. Chemotherapy is a drug treatment that destroys cancer cells and stops them from growing or spreading. It can be given before surgery (neoadjuvant therapy) or after surgery (adjuvant therapy). HER2-directed therapy is often part of adjuvant therapy for women with HER2-positive breast cancer. Hormone therapy reduces the chance of cancer returning by blocking the production of specific breast cells, such as estrogen and progesterone. It is usually combined with neoadjuvant or adjuvant chemotherapy. Side effects vary depending on the type of drug and your age and general health. These include hair loss, nausea and vomiting, fatigue, mouth sores, and rashes. Hormone therapies can also cause hot flashes, vaginal discharge, irritation; irregular periods; decreased sex drive; and, in the case of aromatase inhibitors, joint and muscle pain and increased risk of bone thinning (osteoporosis).
Side Effects
HER2 is a gene that makes a protein that helps cells grow. Cancers that overexpress the HER2 gene make too much of the protein and are more likely to increase and spread into other body parts. HER2-targeted drugs block the growth of these cancers and can prolong survival. Your doctor can tell you if your breast cancer is HER2-positive by looking at a sample of your tumor tissue. The biopsy may be done with fine needle aspiration or core biopsy. Your healthcare provider will anesthetically numb the biopsy site before the procedure. It is essential to understand that HER2 status may change after treatment. This change is called HER2 conversion. Studies have shown HER2 status changes after neoadjuvant chemotherapy (NAC) in about 3.4% of patients. Some of these changes are positive, while others are negative. When HER2 testing is not precise, your healthcare provider will recommend additional tests to determine HER2 status. These include a test that looks at HER2 copy number and a test using an alternative probe for HER2.
Recurrence
Most breast cancers do not come back after treatment, but sometimes cancer cells from your original tumor can break away and hide nearby or spread to other body parts (recur). Your chemotherapy, radiation, or surgery were meant to kill all cancer cells, but some can survive. These recurrences are often not diagnosed because they are too small to show up on tests or cause symptoms. Breast cancers that are HER2-positive tend to grow and spread faster than those that are HER2-negative. HER2-positive breast cancers also respond better to drugs that target the HER2 protein. It is recommended that all invasive neoplastic breast cancers be tested for HER2 status by immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH) before or at the time of diagnosis. The IHC test measures the amount of HER2 protein in a tumor. The results can be 0 to 1+ (HER2 negative), 2+ (borderline HER2-positive), or 3+ (HER2-positive). If the IHC test result is equivocal, a FISH test may be done to help clarify the result. In addition to HER2 status, some breast tissue is also tested for hormone receptors, proteins that send signals to the breast cells to develop. If the tumor is HER2-negative, ER-positive, and PR-negative, it is sometimes called triple-negative breast cancer.
