A major problem of treating leukemia with high-dose chemotherapy and stem cell transplantation is the toxicity of the treatment regimen. High-dose chemotherapy and radiation therapy damage normal cells as well as cancer cells leading to unwanted side effects. Doctors have been seeking more selective ways to deliver therapy to cancer cells while sparing normal cells. One way to deliver radiation is to inject an isotope (a radioactive agent which emits beta or gamma rays). However, this is not specific. Monoclonal antibodies have been developed which react specifically with cancer cells. When an antibody and an isotope are linked together the radiation can be specifically delivered to the cancer cell.

Doctors at the University of Washington and the Fred Hutchinson Cancer Research Center have tested a monoclonal antibody-isotope combination that targets bone marrow cells where leukemia cells are produced. Radiation from the isotope is selectively delivered to the bone marrow without toxic radiation to other normal tissues. They treated 44 patients with leukemia who had previously failed chemotherapy. All patients received the treatment regimen of chemotherapy and total body irradiation followed by the infusion of autologous or allogeneic stem cells. In addition, they then received on average twice as much radiation to the bone marrow from the isotope. This clinical trial was performed primarily to determine the optimal dose of isotope although several patients appeared to benefit from this therapy. Seven of 25 patients with myeloid leukemia survive 7-89 months after treatment and 3 of 9 patients with lymphoid leukemia survive 23-70 months after treatment. This technique can now be applied to patients earlier in their disease when the number of cancer cells is small and resistance to treatment has not developed. (Blood, Vol 94, No 4, pp 1237-1247, 1999)

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