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Bexxar (Tositumomab) for Lymphoma


Updated July 16, 2007

How Bexxar Works

How Bexxar Works

Indranil Mallick MD

What is Bexxar?

Bexxar (tositumomab) is a type of radioimmunotherapy drug that's used for some types of non-Hodgkin's lymphoma. Radioimmunotherapy is a special treatment that combines monoclonal antibody treatment and radiation therapy to kill cancer cells.

How Bexxar Works

Bexxar has two parts:

  • tositumomab -- a monoclonal antibody that recognizes a special molecule called CD20 on the surface of lymphoma cells.
  • iodine 131 -- a radioactive isotope.

The monoclonal antibody portion of Bexxar recognizes the CD20 molecule on the surface of cancer cells. It binds to the molecule and the radiation emitted from the radioactive isotope damages the DNA in the cancer cells and kills them. This form of treatment can target the damage to cancer cells having CD20, and spare normal tissues of the body from side-effects.

When Is Bexxar Used?

Bexxar is approved by the FDA for use in patients with follicular lymphoma whose disease has come back, or who have persistent disease after initial treatment. Those individuals whose slow-growing follicular lymphoma has turned into an aggressive B-cell non-Hodgkin's lymphoma can also be treated with Bexxar. Those who have previously been treated with Rituximab (another monoclonal antibody) may also receive Bexxar.

Bexxar is being studied for different stages of lymphoma, even as initial treatment. (Find more information on clinical trials with Bexxar in the United States.)

How Effective Is Bexxar?

When used in patients who have relapsed after previous treatment in follicular lymphoma, or not responded well to standard treatment, Bexxar has shown a response in nearly 50% to 60% of cases in studies conducted in the US. About 20 to 30% actually showed a complete disappearance of the disease. Disease remained controlled for a year or more in half the patients treated. In some who had a complete response, the lymphoma remained controlled for 4 years or more.

How is Bexxar Given?

Bexxar is given as an injection in the veins. It is usually administered in 2 steps as the "Bexxar therapeutic regimen." The first step involves the injection of the drug over about one and a half hours. Special scans to detect the spread of the medication -- called gamma scans -- are done daily for the first 2 to 3 days after the first injection. If the scans show a good distribution of the drug, a second similar injection is given between 7 to 14 days after the first injection.

Side Effects of Bexxar

The most important side effect of Bexxar is a fall in white blood cell (WBC) and platelet counts. Low WBC counts increase the risk of getting infections. Low platelet counts can cause bleeding from some parts of the body. Studies show that nearly 60% of patients experienced a significant fall in blood counts. This may require a reduction of dose during the second step of treatment.

Allergic reactions to Bexxar can occur in some individuals. Fever, chills, a drop in blood pressure, swelling of the face or the area of injection, and (rarely) breathing difficulty may occur. These can usually be controlled by stopping the infusion and administering medications.

Mild nausea, vomiting and tiredness may also occur. These are temporary and easily treated.

Some individuals treated with Bexxar may develop a blood cancer (leukemia) or a blood condition called myelodysplastic syndrome (MDS) in the years following treatment. It is important to discuss this issue with the physician before treatment starts.

Bexxar may also affect the thyroid gland (a condition called "hypothyroidism") unless it is protected by some medicines administered before and during treatment.

Precautions with Bexxar

Bexxar should only be given by doctors at hospitals that are allowed to use radioactive isotopes. This is because special precautions need to be taken to handle these radioactive compounds before they are given.

Precautions also must be taken to prevent and deal with allergic reactions. A patient may be asked to take some medications beforehand to minimize allergic reactions.

Blood counts are monitored carefully after the treatment.

Medicines to protect the thyroid gland from damage with Bexxar must be administered before and during treatment.

The risks of developing blood disorders -- leukemia or MDS -- must be discussed with the oncologist before treatment.

Bexxar may cause damage to the testes and ovaries -- the organs of reproduction. Fertility may be impaired, and all individuals are asked to use contraceptives during treatment, and for one year after, to lower the risk of birth defects.

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