This study is being done to compare the effects, good and bad, of adding the drug trastuzumab (also called Herceptin®) to breast radiation therapy. Radiation therapy is the standard treatment for patients with ductal carcinoma in situ (DCIS).
This study will find out if adding trastuzumab to breast radiation therapy is more effective than radiation therapy alone in preventing occurrence of breast cancer in the same breast, in the other breast, or in other parts of the body in patients with HER2-positive DCIS.
The drug trastuzumab is called a targeted therapy because it targets breast cancers that make too much of a protein called HER2. These cancers are called HER2-positive. Too much of the HER2 protein can cause cells to receive extra growth signals. This can turn a normal cell into a cancer cell and can cause cancer cells to grow faster.
Trastuzumab has been shown to block the HER2 protein and to slow down or stop the growth of HER2-positive “invasive” breast cancers. ("Invasive" means the cancer has spread outside the milk ducts into other parts of the breast or to other parts of the body.)
Also, there is early information that suggests trastuzumab may be a "radiosensitizer." This means that trastuzumab may help radiation therapy work better in HER2-positive breast cancer. More research is needed to prove