- HER2/neu (HER2) is a tumor protein that appears in almost a third of breast cancers and in several other types of cancers such as colon, prostate and non-small cell lung. Tumors that overexpress HER2 can be associated with a more aggressive cancer, higher recurrence rates, and reduced survival rates. Researchers are testing a therapeutic cancer vaccine designed to stimulate the immune system to recognize HER2. The vaccine, called AdHER2/neu dendritic cell vaccine, is custom-made using an individual s own immune cells. These cells will be collected and used to produce the vaccine.