"Our study opens the door to the possibility that brain tumor patients may live longer and respond better to drug treatments," said Wei Chen, assistant professor in the Department of Molecular and Medical Pharmacology at the David Geffen School of Medicine, University of California, Los Angeles. "Malignant brain tumors are very difficult to treat. Typically, patients live for three months without treatment and up to a year with treatment," she said.
Using positron emission tomography (PET) imaging—with the radiotracer FLT (fluorothymidine)—UCLA researchers were able to determine within one or two weeks after starting the treatment whether patients were responding well to the drugs bevacizumab and irinotecan. This quick response determination "is unheard of" with the traditionally used magnetic resonance imaging, a procedure that looks at the anatomy rather than metabolic activities of tumor cells, she explained. With MRI, it is often difficult to tell tumor growth from changes caused by treatment (such as radiation). In addition, it could take months before it's known whether a patient is responding to treatment, said Chen.
A brain tumor is an abnormal mass of tissue that grows and multiplies uncontrollably—taking up space within the skull and interfering with the brain's vital functions. Malignant brain tumors are rapidly fatal, said Chen. This year, nearly 21,000 people in this country will be diagnosed with brain and other related nervous system tumors in this country and nearly 13,000 individuals will die from them. Neurooncologists are desperately in need of an imaging modality that could evaluate reliably and rapidly the response to a treatment, she added.
"We studied the predictive value of PET with FLT, a marker of cell proliferation, in patients with recurrent malignant brain tumors, said Chen. "We used molecular imaging to measure the changes of metabolism in tumor cells," and FLT-PET provided much higher response rates than MRI, she explained. Additionally, the research shows the FLT-PET imaging is predictive of patients' outcomes—indicating that in those cases where patients responded to drug treatment, they lived three times as long as those who did not, she added. "FLT-PET—as an imaging biomarker—is strongly predictive of overall survival for these patients with brain cancer," she noted. "No matter one's age, number of times cancer recurred or number of prior drug treatments—FLT-PET was the most powerful independent predictor of survival," she said.
The drug bevacizumab is an antiangiogenic agent, which inhibits the development of blood vessels that supply blood and oxygen that contribute to a tumor's growth, said Chen. "Until this study, there were no reliable predictors of therapeutic response for patients with primary brain tumors undergoing treatment with these types of drugs," said Chen. "Our research paves the way for developing drugs that could improve the lives of those with malignant brain tumors," said Chen, adding that research will continue factoring in metabolic response into drug treatment.
PET is a safe, highly specialized, noninvasive imaging technique that uses short-lived radioactive substances to produce three-dimensional images of those substances functioning within the body. A special type of camera works with computers to provide precise pictures of the areas of the body being imaged and molecular images of the body's biological functions.-Society of Nuclear Medicine