Sept. 22 (HealthDay News) -- Leukemia cells can hide in fat tissue to evade chemotherapy, which may explain why obese children with leukemia are more likely to develop chemotherapy resistance and have higher relapse rates, researchers say.

A previous study found that obese children with leukemia are 50 percent more likely to relapse than lean children.

In this new study, researchers observed that obese mice with leukemia had higher relapse rates than lean mice after they were treated with the first-line chemotherapy drug vincristine. In the mice that relapsed, leukemia cells were found to be hiding in fat tissue during chemotherapy.

"We were surprised to find leukemia cells in the fat tissue," lead researcher Dr. Steven D. Mittelman, the fellowship research director with the Division of Endocrinology at Children's Hospital Los Angeles, and assistant professor of pediatrics, physiology and biophysics at the Keck School of Medicine, University of Southern California, said in a news release from the American Association for Cancer Research.

He and his colleagues also found that four chemotherapy drugs used in children -- vincristine, nilotinib, daunorubicin and dexamethasone -- all worked less effectively in culture when fat cells were nearby.

The study appears online Sept. 22 in the journal Cancer Research.

Mittelman said further research is needed to determine how body fat affects chemotherapy.

The study findings offer "striking experimental support for the clinical observations that obesity is associated with poor prognosis in multiple cancers," Dr. David Hockenbery, a member of the Fred Hutchinson Cancer Research Center and a professor of internal medicine at the University of Washington, said in the news release.

SOURCE: American Association for Cancer Research, news release, Sept. 22, 2009