JOHN LEONARD, MD: CD20 is a molecule; it's a protein that's present on the surface of B-cell lymphomas cells. The role or the function of this particular protein in the lymphoma cell is not very clear. But it is evident that the vast majority of patients with the B-cell type of lymphoma—again, the most common, general type—have this target on their lymphoma cells. And, therefore, an antibody that can bind to, can stick to this target and have a variety of different effects on the cell through this target, could result in shrinkage of the lymphoma and, obviously, a benefit to the patient.
ANNOUNCER: The therapeutics used to target the CD20 protein are artificial, or monoclonal, antibodies. They come in two forms: "Naked," which are monoclonal antibodies alone, and monoclonal antibodies that carry a radioactive material.
SANDRA HORNING, MD: Currently, there are three products that are on the market that we consider anti-CD20 monoclonal antibodies. The first is rituximab, also known as Rituxan, which is a naked or unconjugated antibody. And this was the first anti-CD20 antibody that was approved. There are also two conjugated antibodies that have radioisotopes. So these are also known as radioimmunotherapy. Both of them use the anti-CD20 mechanism for targeting. Both of them deliver radiation. These products are known as ibritumomab tiuxetan or Zevalin, or tositumomab, which is known as Bexxar.
ANNOUNCER: Most of the clinical research on monoclonal antibodies in lymphoma has focused on the naked type. Key studies in the mid-1990s showed rituximab improved outcomes for many patients with advanced disease.