One of the difficulties in treating acute myeloid leukemia (AML)
is relapse. Chemotherapy can be intensified to a point before
damaging normal cells. Targeting leukemia cells, however, could
introduce new or more intense agents for more effective cures.
Gemtuzumab ozogamicin (GO), a recombinant humanized anti-CD33
monoclonal antibody, can be linked to calicheamicin, a potent
chemotherapeutic agent for effective immunotherapy. "Calicheamicin
is too toxic given in regular doses to a patient," says Alan Gamis,
MD, chief of the oncology section at Children's Mercy Hospitals and
Clinics. "But in minute amounts, like one molecule attached to one
antibody, that is a dose we can tolerate," he says.
Dr. Gamis, who is chair of the AML committee for the Children's
Oncology Group (COG), also is chairing the randomized phase III
trial, COG AAML0531. The trial enrolled more than 1,000 children
between ages 0 and 21 years from 2006 to 2010 and was open at more
than 200 institutions.
"It was one of the largest childhood AML trials ever performed
where half had GO added to standard treatment and half did not,"
says Dr. Gamis.
After previously showing its safety, this trial seeks to
determine if cure is improved by adding two doses of GO to
intensive chemotherapy regimens during a child's remission
induction and postremission intensification.
"Gemtuzumab was pulled off the market about a year and a half
ago," says Dr. Gamis. A clinical trial in adults to prove the
benefits of one of the FDA's first fast-track agents failed to do
so. That trial had design flaws, however, with subsequent trials
now demonstrating effectiveness.
"We've also learned that AML is not just one leukemia," he says.
It appears as if the targeted agent works effectively in some but
not all forms of AML. Results from the COG safety trial, AAML03P1,
which enrolled 350 children, were released in the February 1 issue
of Cancer. These show improved survival overall and show
GO can be added safely. "Data from AAML0531 to determine if GO
definitely improves cure will be released next spring," says Dr.
The leadership roles of Dr. Gamis and Children's Mercy in COG
and other trial groups offer opportunities for physicians to refer
Kansas City and Midwest patients to trials for the most advanced
treatments possible for diseases such as AML.
"The most recent results show an overall survival rate for AML
of about 65 percent," says Dr. Gamis. "This was a leukemia that in
1985 or so only had about a 20 percent cure rate. It has improved
considerably over the last several decades."