Immunohistochemistry (IHC) testing is a laboratory technique used to understand breast cancer. It involves using antibodies to detect specific proteins, or biomarkers, within a tissue sample, typically obtained during a biopsy or surgery. IHC identifies unique tumor characteristics. This information helps medical professionals understand cancer behavior and guides effective treatment choices.
Key Markers Identified by IHC
IHC tests for breast cancer focus on several biomarkers: Estrogen Receptor (ER), Progesterone Receptor (PR), Human Epidermal growth factor Receptor 2 (HER2), and Ki-67. These proteins are found either on the surface of breast cancer cells or within them. Their presence, absence, or quantity provides valuable information about the tumor’s biology.
Estrogen Receptor (ER) and Progesterone Receptor (PR) are proteins that bind to estrogen and progesterone. If present, these receptors allow hormones to stimulate cancer growth. Testing determines if growth is hormone-influenced. HER2 is a protein involved in cell growth and division; increased levels can signal aggressive tumor growth.
Ki-67 is a protein located within the cell nucleus and indicates rapid cell division. A higher percentage suggests a faster-growing tumor. These markers provide a comprehensive breast cancer profile, guiding diagnostic and treatment decisions.
Understanding Your IHC Results
Results for IHC markers are reported in various ways. For Estrogen Receptor (ER) and Progesterone Receptor (PR), results are given as positive or negative, often with a percentage. A positive result indicates receptor presence, with the percentage reflecting the proportion of affected cancer cells. A high percentage suggests the tumor is sensitive to hormones.
HER2 results are reported on a scale from 0 to 3+. A score of 0 or 1+ means the cancer is HER2-negative, indicating little to no HER2 protein. A score of 2+ is “equivocal” or “borderline,” meaning HER2 status is unclear and requires further FISH (fluorescence in situ hybridization) testing for confirmation. A score of 3+ indicates the cancer is HER2-positive, meaning it has a high level of HER2 protein.
Ki-67 results are expressed as a percentage, representing the proportion of cancer cells that are actively dividing. A higher Ki-67 percentage suggests a more aggressive tumor with faster growth.
IHC’s Role in Breast Cancer Treatment
IHC testing results directly influence breast cancer treatment. If the tumor is Estrogen Receptor (ER) and/or Progesterone Receptor (PR) positive, hormone therapy is an option. These therapies, like tamoxifen or aromatase inhibitors, block hormones from reaching cancer cells or reduce the body’s hormone production, inhibiting growth.
For HER2-positive breast cancer, targeted therapies are available. Medications like trastuzumab (Herceptin) target the HER2 protein on cancer cells, hindering growth and signaling. These treatments are more precise, focusing on cancer cells while minimizing harm to healthy cells. The Ki-67 index also guides treatment decisions, particularly in hormone receptor-positive cancers. A high Ki-67 percentage, indicating rapid cell division, may suggest greater benefit from chemotherapy, either before or after surgery.
IHC testing supports personalized medicine in breast cancer care. By identifying the unique molecular characteristics of an individual’s tumor, healthcare providers can tailor more effective and potentially less toxic treatment plans. This approach ensures therapies are chosen based on the tumor’s biological profile, leading to improved patient outcomes.