Growth factor stimulates platelet
Cancer patients who received a novel growth factor after undergoing chemotherapy
showed a 70 percent increase in blood platelet levels compared to patients
not exposed to the growth factor, Emory researchers and others reported
in The New England Journal of Medicine. In addition, platelet counts of
exposed patients returned to normal levels significantly faster than did
counts in patients unexposed to the growth factor.
count after chemotherapy
"Our findings suggest that for the first time doctors have the means
to stimulate the production of platelets depleted by chemotherapy,"
said principal investigator Michael Fanucchi, an associate professor in
the Department of Medicine. "Not only may giving the growth factor
after chemotherapy reduce risks associated with low platelet counts such
as bleeding, it may also allow oncologists to use chemotherapeutic agents
more effectively by administering stronger or more frequent doses."
The investigational growth factor is polyethylene glycol-conjugated recombinant
human megakaryocyte growth and development factor (MGDF). It is Amgen Inc.'s
proprietary, recombinant human form of the major regulator of platelets
in the blood. Amgen, of Thousand Oaks. Calif., isolated and cloned MGDF
and has refined a method of utilizing recombinant technology to manufacture
large quantities of the platelet-producing protein.
During the Phase I/II randomized and double-blinded clinical trial, investigators
at Emory, UCLA and Duke University evaluated the tolerance and effect on
platelets of MGDF in persons with advanced nonsmall-cell lung cancer. After
all 53 patients underwent chemotherapy with paclitaxel (Taxol) and carboplatin,
40 received MGDF and 13 received placebo.
Among 38 MGDF patients, the researchers documented a median low platelet
count of 188,000 per cubic millimeter-a 70 percent increase over the median
low count of 111,000/cmm measured among the unexposed patients. Still more
important to the researchers was the finding that platelet counts in the
MGDF patients returned to normal within 14 days-a significantly more rapid
recovery than the 21 days or longer measured among patients receiving placebo.
Two of the patients developed blood clots, perhaps related to the increased
platelet production induced by MGDF.
Platelets are disc-shaped components of blood that are smaller than red
blood cells and contain no hemoglobin. They promote clotting; therefore,
when low, the body is at risk for excessive bruising and bleeding. Many
chemotherapeutic agents, including carboplatin, can reduce platelet counts
to dangerous levels (50,000/cmm or lower). Low platelet counts can be corrected
by transfusions. Transfusions, however, bring further risks of possible
infectious or allergic complications.
"The development of MGDF represents a potentially important addition
to the armamentarium for managing patients receiving myelosuppresive chemotherapy,"
said Laurence A. Harker, director of the Division of Hematology-Oncology
in the Department of Medicine and a co-author of the paper. "It can
be combined with other growth factors such as G-CSF, which stimulates production
of white blood cells, and erythropoietin, which drives the production of
red blood cells."
The majority of lung cancer patients have nonsmall-cell cancer that is not
diagnosed until the later stages, stages III and IV, when chemotherapy is
especially vital to prolonging survival. "We look forward to expanding
the role of this agent in future chemotherapeutic trials," said Christopher
D. Hillyer, deputy director of Winship Cancer Center.
Lung cancer is the leading cause of cancer death in men and women. Approximately
160,400 Americans will die from lung cancer in 1997, and 178,100 new cases
will be diagnosed, according to the American Cancer Society's Cancer Facts
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