Doctors use a variety of methods to rid the body of cancer cells. Skilled cancer surgeons remove tumors, beams of conventional radiation kill cells in the line of beam's path, and chemotherapy eliminates the body's rapidly dividing cells. Because many of these treatments are imprecise, they produce many unpleasant side effects. Still, all of these treatments can be effective, offering an improved outcome and, in some cases, even a cure.
But today researchers are designing drugs that seek and destroy just cancer cells, sparing healthy cells. Targeted drug therapies known as monoclonal antibodies are already available to patients with certain types of cancers. These drugs have a particular affinity for proteins only found on the surface of certain cancer cells. Two monoclonal antibodies are now being used for the treatment of non-Hodgkin's lymphoma, a cancer that starts in the lymphatic tissue. Below, Dr. Stephanie Gregory, professor of medicine at the Rush Medical College in Chicago, and Dr. Robert Dillman, medical director of the Hoag Cancer Center in Newport Beach, California, review the benefits of targeted therapy for non-Hodgkin's lymphoma and how this unique medication can be used to deliver a dose of radiation directly to the cancer cells in a new approach known as radioimmunotherapy.
What is a targeted therapy?
STEPHANIE GREGORY, MD: A targeted therapy is something that actually goes in and hits a cancer cell and preserves the normal cells. It is distinct from chemotherapy, which hits all cells, especially the rapidly dividing cells, so you get toxicities with regular chemotherapy that you don't get with targeted therapy.
What are the main targets in non-Hodgkin's lymphoma?
STEPHANIE GREGORY, MD: The main targets in non-Hodgkin's lymphomas are proteins on the surface of certain immune cells. The targets are mostly the proteins on the surface of B cells, though there are some targeted therapies against T cells also.
What kinds of targeted treatments are available?
ROBERT DILLMAN, MD: The main targeted agents are called monoclonal antibodies. Our bodies make antibodies in our everyday life to help fight against foreign invasion and infections. To produce monoclonal antibodies to use as a treatment, researchers make antibodies that will target and bind to certain molecules on tumors. Some of these antibodies are made in mice, then, using technology, the mouse antibodies are reengineered to make them more human-like.
STEPHANIE GREGORY, MD: The main targeted therapy that's been on the market is a monoclonal antibody that targets a protein on the surface of non-Hodgkin's lymphoma cells called CD20. This therapy is used in people with low-grade non-Hodgkin's lymphomas.
What is radioimmunotherapy?
STEPHANIE GREGORY, MD: A radioimmunotherapy is a monoclonal antibody that has radioactive material attached to it. Radiation penetrates deep into the tumor.
How does radioimmunotherapy differ from conventional radiation therapy?
ROBERT DILLMAN, MD: Conventional radiation therapy is done with an external beam radiation that is directed to a specific site on the body. In order to improve external beam radiation, you have to get a more precise field. The problem is that you have to know what you're aiming for, so you have to be able to see the cancer on some sort of a scan.
The beauty of antibody-targeted therapy is you can treat areas that you can't even see. To do that with external beam radiation, you'd have to treat the whole body, and you can't give adequate doses without harming normal tissue.
How do the side effects compare to chemotherapy?
ROBERT DILLMAN, MD: If you look at the toxicity profile of radioimmunotherapy compared to chemotherapy, at first blush, they are similar in that they both suppress bone marrow cells. A lot of chemotherapy side effects, such as loss of hair, nausea and vomiting, skin rashes, neuropathy, numbness and tingling, typically are not problems with the radioimmunotherapy. The only side effects that have been seen are bone marrow suppression, and ones associated with the initial infusion when the drug reacts with circulating cells. One should also watch for long-term delayed effect from the radiation.
What do you see for the immediate future of the targeted therapy?
STEPHANIE GREGORY, MD: The future of targeted therapy is very bright. We are going to see more and more combinations of targeted therapy. Many new monoclonal antibodies are being developed, and I believe that a combination of new and old therapies will be used in the future.
ROBERT DILLMAN, MD: I think targeted therapy for non-Hodgkin's lymphoma will become a standard part of the treatment of this disease. It wouldn't surprise me if, within about a decade, we are primarily using antibodies and antibody targeted treatments, and much less of the nonspecific chemotherapy that we currently use.
