Recurrent AML: Antibody-Targeted Therapy, Gemtuzumab Ozogamicn, under FDA Review

A new approach to cancer treatment, called antibody-targeted chemotherapy, may offer expanded treatment options to older persons who have a recurrence (return) of acute myeloid leukemia. A drug called gemtuzumab ozogamicin, an antibody linked to an anti-tumor antibiotic, is currently undergoing priority review by the U.S. Food and Drug Administration (FDA) for this indication.

Acute myeloid leukemia (AML) is a cancer of the blood cells in the bone marrow. The bone marrow contains early blood-forming cells, called stem cells, which grow and mature into the 3 blood cell types: white blood cells (protect the body from infection), red blood cells (carry oxygen to the tissues), and platelets (help the blood to clot). In the case of leukemia, too many cells of 1 type are produced in the bone marrow, resulting in an excess of abnormal, immature cells of this type. These cells crowd out other blood cells, and may invade other parts of the body, including the blood stream, lymph system, and vital organs. There are 2 types of myeloid leukemia, acute and chronic.

Acute myeloid leukemia progresses more quickly than the chronic type. Treatment is usually chemotherapy, but may also include radiation therapy, biologic therapy to help the immune system, or high-dose chemotherapy followed by a stem cell transplantation.

Now, a new approach to the treatment of AML called antibody-targeted chemotherapy, is emerging. Most persons who have AML have substances (or glycoproteins), called CD33 antigens, present on the cancerous leukemia cells. The agent gemtuzumab ozogamicin consists of an antibody and an anticancer antibiotic (or immunotoxin), called calicheamicin. The antibody specifically targets the CD33 antigen, and therefore also the leukemia cells, and the calicheamicin then kills the leukemia cells. It is believed that this therapy may have fewer or less severe side effects than the standard chemotherapy regimens, making it particularly beneficial to older persons who cannot tolerate the more toxic treatments.

In 1 study, 23 persons with recurrent AML were treated with gemtuzumab ozogamicin, resulting in elimination of leukemia cells from the blood and bone marrow, with fewer side effects than standard chemotherapy regimens. In another study, researchers from several medical centers treated 142 persons who had a recurrence of AML with gemtuzumab ozogamicin. Results showed that 30% of these persons responded to treatment. Because of these findings, the FDA granted the agent priority review status.

On March 17, 2000, the FDA Oncologic Drugs Advisory Committee voted to support an accelerated approval process for gemtuzumab ozogamicin for use in persons, 60 years and older, who have recurrent AML that is positive for the CD33 antigen. If the FDA does approve gemtuzumab ozogamicin, it will be the first approved antibody-targeted chemotherapy agent, and will provide an additional treatment option for older persons with AML.

Persons 60 years and older who have AML may wish to talk with their doctor about the risks and benefits of receiving gemtuzumab ozogamicin or of participating in a clinical trial in which other promising new therapies are being studied. Sources of information on ongoing clinical trials that can be discussed with a doctor include a comprehensive, easy-to-use service provided by the National Cancer Institute (cancer.gov) and the Clinical Trials section and service offered by Cancer Consultants.com (www.411cancer.com).

(Seminars in Hematology, Vol 36, No 4, suppl 6), pp 2-8, 1999)

(Blood, Vol 93, No 11, pp 3678-3684, 1999)

(American Home Products, FDA Advisory Committee Recommends Approval of First Antibody-Targeted Chemotherapy, www.ahp.com, 2000)

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