(The New York Times News Service) -- When 14-year-old Marcus Quillen of Irving, Texas, had surgery to remove a brain tumor in 1999, doctors had no way to predict whether it would return.

Now they do.

Research conducted at the University of Texas Southwestern Medical Center at Dallas indicates that the presence of a protein called Ki-67 can forecast whether the most common type of childhood tumor will grow or return after surgery.

Tumors with a lot of the Ki-67 antigen are more aggressive and more likely to grow than tumors with a little, said Dr. Daniel Bowers, assistant pediatrics professor and lead author of a study published in the August edition of the "Journal of Clinical Oncology." The Virginia-based journal is published by the American Society of Clinical Oncology.

"If a child has a large amount of Ki-67, then the tumor is at a much higher risk of progressing, and that child needs to be watched more closely," Bowers said. "It gives us a more clear picture of what is going on with these kids."

In North Texas, 30 to 40 children are diagnosed with the tumor, pilocytic astrocytoma, each year, Bowers said. The slow-growing tumor is usually benign, according to the National Brain Tumor Foundation in Oakland, Calif.

The tumor is the most common childhood brain tumor; about 1,100 children in the United States are diagnosed with pilocytic astrocytomas annually. The average age of pilocytic astrocytoma patients is 7.

Although they are usually not life-threatening, such tumors can cause speech and balance problems and seizures. Children typically develop symptoms that can include headache or vomiting as the tumor gradually presses the brain.

When Marcus Quillen reported having neck and shoulder pain, his mother believed that he had a strained muscle playing baseball. Then he developed nausea, which his doctor attributed to a virus. When his symptoms did not improve, his doctor suspected a sinus infection and ordered a computerized tomography scan.

The tumor was detected and he underwent surgery.

Most children do well after surgery, even if the tumor is not completely removed, Bowers said. But about 30 percent of the time, the tumor's growth progresses.

Findings from the latest study should provide doctors with an important prognostic tool, Bowers said. The Health Insurance Portability and Accountability Act prevents Bowers from saying whether Quillen is participating in the study, but his condition would qualify him for it.

"This finding already makes a difference in how we treat patients," Bowers said. "Now, we can either go back for another surgery or intervene earlier with radiation or chemotherapy."

Dr. Linda Margraf, a UT-Southwestern associate professor of pathology and the study's senior author, said the test to determine a child's recurrence risk is time-consuming but beneficial. Most pathology labs can perform the procedure, she said.

Virginia Quillen said her son is doing well now and will be a freshman at Irving High School this year. He undergoes a magnetic resonance imaging scan every six months to check for recurrences.

"We're very confident what we did has taken care of his tumor, and we're not expecting any kind of reoccurrence," she said. "But it would be very helpful knowing how to treat it if it did" recur.

PILOCYTIC ASTROCYTOMA

About 1,100 children are diagnosed with these slow-growing tumors in the United States each year. The tumors are considered benign because they typically do not invade the brain tissue. Treatment usually includes surgery, radiation and chemotherapy.

Signs and symptoms include:

- Balance and coordination problems

- Hydrocephalus, in which fluid collects in the brain

- Headache, nausea or vomiting

- Speech problems

- Seizures

Copyright 2003 The New York Times News Service. All rights reserved.