New Biologic Therapy, Iodine I 131 Tositumomab, Effective against Lymphoma

New Biologic Therapy, Iodine I 131 Tositumomab, Appears Effective against Previously Untreated Low-Grade Lymphoma

The results of a recent study offer promise for the use of a new biologic therapy, iodine I 131 tositumomab, to treat persons with newly diagnosed low-grade advanced follicular lymphoma, according to researchers at the American Society of Clinical Oncology annual meeting in May 2000. Tositumomab is a monoclonal antibody, linked to a radioactive toxin, that attaches to a protein present on lymphoma cells. The monocolonal antibody provokes an immune system attack against the lymphoma cells at the same time that the attached radioactive toxin also targets and kills those cells.

Follicular lymphoma is a type of

non-Hodgkins lymphoma. Non-Hodgkins lymphoma (NHL) is a cancer of the lymph tissue, which is present in the lymph nodes, lymph vessels, bone marrow, and organs such as the thymus, tonsils, and spleen. One of the main cells in the lymph system is the

lymphocyte, of which there are 2 types: B and T cells. The large majority of NHL cases involve cancer of the

B lymphocytes, characterized by the rapid, excessive multiplication of these cells (sometimes referred to as

B-cell NHL or B-cell lymphoma). While NHL is categorized by the type of lymphocyte it involves, it is also further defined by the specific appearance of the affected cells, as well as the grade (how fast it is likely to grow) of the disease, based on how the cells look under a microscope. In terms of NHL grade,

low-grade NHL is the slowest growing,

intermediate-grade NHL is fast growing, and

high-grade NHL is the fasted growing. The term follicular lymphoma refers to NHL in which the cancer cells appear clustered together, rather than being further apart, under the microscope. Follicular lymphoma may be either low or intermediate in grade.

The treatment options for follicular lymphoma depend on the specific type, grade, and stage (extent of disease at diagnosis) of disease, but may include: no therapy until symptoms appear, radiation therapy alone, chemotherapy alone, Rituxan®, a monoclonal antibody, or a combination of therapies. Treatments using new chemotherapy drugs; high doses of chemotherapy/radiation therapy with a stem cell transplantation; and other types of biologic therapies are being studied in clinical trials. A relatively new biologic therapy, called iodine I 131 tositumomab, has recently produced positive results for persons with newly diagnosed follicular lymphoma.

Iodine I 131 tositumomab is a monoclonal antibody, linked to a radioactive toxin. The monoclonal antibody component targets and binds to a protein, called

CD20, which is present on the surface of B cells (or B lymphocytes). This binding provokes the bodys immune system to attack those B cells, while at the same time the radioactive toxin acts to destroy the same B cells to which it is now attached. Since most lymphomas involve cancer of the B-cell lymphocytes, this treatment strategy allows the delivery of greater amounts of radiation to the cancer cells, while minimizing radiation exposure to normal cells.

Researchers from Michigan and California treated 76 persons with newly diagnosed low-grade advanced follicular lymphoma. All patients received a single infusion of iodine I 131 tositumomab. Responses occurred in 97% of patients, with 63% being complete responses and 34% being partial responses. After 3 to 16 months, 13 of 26 patients having partial responses, and 45 of 48 patients having complete responses, have not yet had any progression of their disease.

From these findings, it appears that a single infusion of iodine I 131 tositumomab is highly effective as an initial treatment against low-grade advanced follicular lymphoma in persons who have not previously received treatment. Persons who have this type of disease may wish to talk with their doctor about the risks and benefits of participating in a clinical trial in which iodine I 131 tositumomab as an initial treatment or other promising new treatment strategies are being studied. Two sources of information on ongoing clinical trials include clinical trials listing services provided by the National Cancer Institute (

cancer.gov) and

eCancerTrials.com. eCancerTrials.com also performs personalized clinical trial searches on behalf of patients. (

Proceedings of the American Society of Clinical Oncology Thirty-Sixth Annual Meeting, Vol 19, Abstract 11, p 5a, 2000)

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