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Antibody-Targeted Chemotherapy with Mylotarg Shows Promise for Many Adults with Deadly Form of Leukemia

Fred Hutchinson Cancer Research Center Researcher Presents Updated Study Results at the American Society of Clinical Oncology Meeting in New Orleans

NEW ORLEANS, MAY 21, 2000 The first ever antibody-targeted chemotherapy induced remission in a sizable number of adult patients with advanced leukemia, according to data presented by a Fred Hutchinson Cancer Research Center investigator today at the 36th Annual Meeting of the American Society of Clinical Oncology (ASCO). The drug, Mylotarg (gemtuzumab ozogamicin for injection), was recently approved by the U.S. Food and Drug Administration (FDA) to fight relapsed acute myeloid leukemia (AML) for some patients age sixty and older.

AML is a virulent and often fatal form of cancer in which certain white blood cells become cancerous and rapidly accumulate in the bone marrow, preventing normal marrow from growing and functioning properly. It is among the most serious forms of adult leukemia, with a relatively high fatality rate.

"Mylotarg is a new option for many adult patients with AML," said Eric Sievers, M.D., of Fred Hutchinson Cancer Research Center. "Patients greater than 60 years of age achieved remission at a comparable rate to younger patients. If a patient has CD33 positive AML that has relapsed, Mylotarg is worth considering."

Most patients with AML require intensive standard chemotherapy to achieve remission, and some also must undergo bone marrow transplants. Even after such intensive treatment, up to half of all AML patients have residual leukemic cells or experience a relapse. Because standard chemotherapy drugs to treat AML are non-specific - destroying normal as well as malignant cells - patients who receive the therapy tend to become very sick. Researchers at the Fred Hutchinson Cancer Research Center, and eleven other leading leukemia centers, including University of Chicago Medical Center, MD Anderson Cancer Center, The University of Pennsylvania Cancer Center, Wayne State University, and the City of Hope Medical Center, are working with Wyeth-Ayerst Laboratories and Celltech Chiroscience to study Mylotarg, an antibody-drug conjugate that targets chemotherapy treatment to leukemia cells. In clinical trials, Mylotarg has been referred to as CMA-676.

Mylotarg is the first in a new class of anticancer therapy called antibody-targeted chemotherapy. Mylotargs highly specific antibody recognizes a cell-surface molecule called "CD33" which is abundant on AML cells but absent from normal blood stem cells, the seeds from which normal blood and immune cells originate. This engineered antibody is linked to a novel and extremely potent chemotherapy agent known as "calicheamicin". The antibody selectively targets leukemic blast cells and delivers calicheamicin to them. As a result, the leukemic cells are destroyed but the cells that are responsible for replenishing normal blood cells are spared.

Pooled data from three Phase II clinical trials reported on 104 patients, each of whom had CD33 positive AML in first relapse. Mylotarg produced remission in 31 percent of patients - a rate comparable to that of standard combination chemotherapy regimens - with mild and tolerable side effects. When evaluating the patients with respect to age, remission was achieved in 34 percent of patients under 60, and 28 percent of patients sixty and older. There were no clinically significant differences in side effects between the age groups.

"Most striking was the near absence of severe mucositis, or mouth sores seen in association with Mylotarg treatment," Sievers continued. "While standard chemotherapy induction is usually associated with a prolonged hospital admission, one-sixth of the patients who received Mylotarg were hospitalized for less than a week."

Standard combination chemotherapy treatment often produces significant major organ damage, and sores both in the mouth and in the intestinal tract (frequent sources for opportunistic infections), but Mylotarg treatment does not. Mylotarg also is associated with a relatively low treatment-related mortality. As with standard chemotherapy treatments, Mylotarg produces a temporary suppression of bone marrow and blood cell counts.

Mylotarg is administered in two IV infusions fourteen days apart, and many patients have received the drug on an outpatient basis. Unlike standard chemotherapy regimens, which involve multiple drugs, Mylotarg was given alone.

The Fred Hutchinson Cancer Research Center is an independent, non-profit research institution dedicated to the development and advancement of biomedical technology to eliminate cancer and other potentially fatal diseases. Recognized internationally for its pioneering work in bone marrow transplantation, the Center has four scientific divisions collaborating to form a unique environment for conducting basic and applied science. One of 35 National Cancer Institute-designated comprehensive cancer centers in the country, it is the only one in the Northwest. Visit the Hutchinson Center web site for more information at www.fhcrc.org.

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Editor's Note: Backgrounders are available on the CD33 monoclonal antibody and calicheamicin.

For information about Wyeth-Ayerst Laboratories, contact: Douglas Petkus, 610/971-4980.

Mylotarg: Mylotarg is a trademark of American Home Products Corp.

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The Fred Hutchinson Cancer Research Center is an independent, nonprofit research institution dedicated to the development and advancement of biomedical technology to eliminate cancer and other potentially fatal diseases. Recognized internationally for its pioneering work in bone-marrow transplantation, the Center's four scientific divisions collaborate to form a unique environment for conducting basic and applied science. The Hutchinson Center is the only National Cancer Institute-designated comprehensive cancer center in the Pacific Northwest. For more information, visit the Center's Web site at <www.fhcrc.org>.

Contact: Susan Edmonds
206/667-2896
sedmonds@fhcrc.org

Fred Hutchinson Cancer Research Center is a world leader in research to prevent, detect and treat cancer and other life-threatening diseases.