HER2 is a protein that's made by breast cells. In about 20 to 25 percent of women with breast cancer, the cancer cells over-express the HER2 protein. These cancers, labeled HER2 positive, tend to grow faster and are more likely to come back than breast cancers that don't overproduce the HER2 protein.
Herceptin® (trastuzumab) is a drug that was approved in 1998 for treatment of HER2 positive metastatic breast cancer (cancer that has spread to other parts of the body). The drug works by binding to the part of the HER2 protein that extends outside the cancer cell, blocking the action of the HER2. That stops the messages that tell the cancer cells to grow. Herceptin is not a cure for breast cancer. It may extend the survival of women with metastatic HER2 positive breast cancers. But even this drug isn't a magic bullet. Eventually, many HER2 positive breast cancers become resistant to the drug.
In March, the FDA approved an oral medication for HER2 positive metastatic breast cancer, called Tykerb® (lapatinib). Like Herceptin, Tykerb also targets the HER2 protein. However, Tykerb targets the part of the protein on the inside of the cancer cell. The new drug also has a second target on the cancer cell, epidermal growth factor receptor (EGFR). Overexpression of EGFR leads to uncontrolled growth of cells.
Tykerb is taken in combination with another anti-cancer drug, Xeloda® (capecitabine). Studies show the two medications can reduce the risk of disease progression by more than 50 percent and prolong survival time for patients. Side effects tend to be mild and can include diarrhea, vomiting, nausea, tiredness, mouth sores, loss of appetite, indigestion and development of painful red hands or feet. In rare cases, Tykerb may cause an abnormal heart rate, weakening of the heart muscle or respiratory problems.
Currently, Tykerb is approved for patients with metastatic HER2 positive breast cancer who have tried and failed treatment with other chemotherapy drugs and Herceptin. Researchers say that by targeting two sources on the cancer cell (HER2 and EGFR), the cancer may be less likely to develop a resistance to Tykerb.