Why do I need HER2 breast cancer testing?If you've been diagnosed with breast cancer, you may need this test to find out if your cancer is HER2-positive or HER2-negative. If you are already being treated for HER2-positive breast cancer, you may need this test to:Find out if your treatment is working. Normal levels of HER2 may mean you are responding to treatment. High levels may mean the treatment is not working.Find out if cancer has come back after treatment.
