Breast cancer is a complex disease, and understanding its specific characteristics is important for effective treatment. One such characteristic involves a protein called human epidermal growth factor receptor 2, or HER2. This protein is found on the surface of breast cells, and its presence in high amounts can influence how breast cancer develops and responds to therapies, guiding tailored treatment strategies.
Understanding HER2 in Breast Cancer
The HER2 gene provides instructions for making the HER2 protein, which is a receptor located on the surface of cells. In healthy cells, these HER2 proteins play a role in regulating cell growth, division, and repair. They act like antennae, receiving signals that tell the cell when to grow and divide in a controlled manner.
In some breast cancers, the HER2 gene becomes amplified, meaning there are too many copies of the gene within the cancer cells. This leads to an excessive production of the HER2 protein, known as HER2 overexpression. Too many HER2 receptors on the cell surface send constant signals for cells to grow and divide uncontrollably, contributing to rapid tumor growth and a more aggressive form of breast cancer. Approximately 15% to 20% of invasive breast cancers exhibit HER2 overexpression.
Determining HER2 Status
To determine if a breast cancer is HER2-positive, laboratory tests are performed on tumor tissue, typically obtained from a biopsy or during surgery. One common method is Immunohistochemistry (IHC), which uses special stains to detect the amount of HER2 protein on the surface of cancer cells. IHC results are reported on a scale from 0 to 3+, where 0 or 1+ indicates HER2-negative, 2+ is considered borderline or equivocal, and 3+ signifies HER2-positive.
If the IHC result is equivocal (2+), an additional test called Fluorescence In Situ Hybridization (FISH) or other in situ hybridization (ISH) tests may be used. FISH directly measures the number of HER2 gene copies within the cancer cells. A HER2-positive result by FISH means the ratio of HER2 gene copies to a control gene is 2.0 or higher.
Treatment for HER2-Positive Breast Cancer
Treatment for HER2-positive breast cancer often involves targeted therapies that specifically aim to block the activity of the HER2 protein. Monoclonal antibodies like trastuzumab and pertuzumab are frequently used; trastuzumab binds to the HER2 receptor, preventing it from receiving growth signals, while pertuzumab targets a different part of the HER2 protein, inhibiting its ability to pair with other receptors.
Another class of drugs, antibody-drug conjugates (ADCs), combines a HER2-targeting antibody with a chemotherapy drug. Examples include trastuzumab emtansine (T-DM1) and fam-trastuzumab deruxtecan. These ADCs deliver chemotherapy directly to HER2-positive cancer cells, minimizing damage to healthy cells. Tyrosine kinase inhibitors, such as lapatinib and tucatinib, are small molecules that block signaling pathways inside the cell initiated by the HER2 receptor. These targeted therapies are administered in combination with traditional chemotherapy or other systemic treatments to enhance effectiveness.
Outlook for HER2-Positive Breast Cancer
The development of HER2-targeted therapies has changed the outlook for individuals with HER2-positive breast cancer. Before these specific treatments were available, HER2-positive breast cancer was associated with a more aggressive disease course and a higher risk of recurrence. However, the introduction of drugs like trastuzumab has improved patient outcomes.
Patients diagnosed with HER2-positive breast cancer now experience better survival rates and a reduced likelihood of the cancer returning. The effectiveness of these targeted therapies means that the prognosis for HER2-positive breast cancer is now comparable to, or more favorable than, some types of HER2-negative breast cancer. This advancement highlights the impact of precision medicine in transforming cancer care.