HER2-positive breast cancer is a subtype of breast cancer that contains human epidermal growth factor receptor 2 (HER2), which is a protein that increases the growth of cancer cells. One out of five breast cancers contain the HER2 protein. Eighteen-to-twenty percent of invasive breast cancers are HER2-positive, which are more aggressive than other breast cancers, more likely to spread and relapse, and have resulted in a decreased survival rate in the past. While previously considered to be the most aggressive type of breast cancer, HER-2 positive breast cancer can now be treated with new biologic targeted therapies that have significantly improved outcomes.
HER2-positive breast cancer is categorized in stages that take into account the diameter of the tumor, whether the cancer has spread to axillary (underarm) lymph nodes, and whether the cancer has spread to other organs, such as the liver, lung, brain and bone. Staging allows for treatment plans that target each patient’s individual breast cancer disease.
Early breast cancers are staged based on the following criteria:
Stage 0 – Ductal cancer in situ (DCIS), or a noninvasive breast cancer that is limited to the ducts.
Stage I (A/B) – Cancer has spread from ducts to the surrounding fatty breast tissue. Tumor is smaller than 2 centimeters and has not spread to lymph nodes.
Stage II (IIA/B) – Cancer has spread from ducts to the surrounding fatty breast tissue and may have spread to near lymph nodes. Tumor is between 2-to-5 centimeters wide.
Advanced breast cancers are staged based on the following criteria:
Stage III (IIIA/B) – The tumor is larger than 5 centimeters, cancer may or may not have spread to lymph nodes, or the tumor is smaller, and cancer has spread to lymph nodes.
Stage IV – Metastatic Breast Cancer. Cancer has spread to lymph nodes and other parts of the body, with other organs affected, such as liver, lungs, brain, or bones.