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What is Skeletal Targeted Radiotherapy?

Skeletal Targeted Radiotherapy is an experimental therapy that is being developed by NeoRx Corporation for the treatment of patients with multiple myeloma. The scientific name of the drug is 166Ho-DOTMP.

How does Skeletal Targeted Radiotherapy work?

There are two important components of 166Ho-DOTMP. The first is DOTMP, a chemical that collects in bones. The other component of 166Ho-DOTMP is radioactive holmium, abbreviated 166Ho. 166Ho is a radioactive particle that is bound to the DOTMP. Certain types of cells in the body, such as many cancer cells, are sensitive to radioactivity and can be killed if they are close to a radioactive particle such as 166Ho. These properties make 166Ho-DOTMP a potentially useful drug for the treatment of cancers in the bone. When the drug collects in the bone, it will expose cells there to 166Ho, killing cancer cells.

What diseases can be treated with Skeletal Targeted Radiotherapy?

Right now, clinical trials are being done to test whether STR is a useful treatment for multiple myeloma. The cancer cells in multiple myeloma are often found in the bone or bone marrow, and are sensitive to radiation, so STR might be able to kill the cancer cells. In the future, it is possible that STR could be used for other types of cancer that are found in bone, such as Ewing's sarcoma or osteosarcoma.

What are the steps of treatment with STR?

First, a tracer is given to be sure that enough 166Ho-DOTMP goes to the bone in each patient. To test this, a small dose of 166Ho-DOTMP is injected into the patient, and tests are done to show where the 166Ho ends up. After this step, patients are treated with a larger dose of STR, and with a drug often used in myeloma called melphalan. The combination of 166Ho-DOTMP and melphalan will hopefully kill cancer cells, but will also kill other bone marrow cells. Because of this, patients who receive STR in clinical trials will receive a stem cell transplant to replace their bone marrow cells. After treatment, the patient will be carefully watched for side effects and to see how their cancer responds.

Have other patients been treated with Skeletal Targeted Radiotherapy?

Yes. 83 patients were treated with STR in two clinical trials performed by NeoRx. Many (64%) of these patients had reduced cancer after the treatment, and 35% of them had no detectable disease for at least a while after treatment. The improvements lasted different lengths of time in different people.

What are the risks and side effects of STR?

In the clinical trials performed by NeoRx, some people experienced bladder problems. Almost all of the patients who experienced these problems did not have a procedure called "continuous bladder irrigation," that helps flush extra radioactivity from the body. All patients who are treated with STR will now get continuous bladder irrigation. Some patients also experienced kidney problems. Most of the kidney problems happened at the highest doses of STR, and these high doses will not be used anymore. Still, STR is an experimental drug and other unexpected side effects could occur. Other side effects, such as nausea and vomiting, could also occur. If you decide to participate in a trial of STR, you will be completely informed of up-to-date information on side effects.

Are there any ongoing trials of STR?

Yes. A trial is going on at 5 transplant centers across the US. Another study at more centers is planned to begin in early 2003.

How can I get more information about STR and ongoing trials?

You can get more information from NeoRx and from ClinicalTrials.gov.