High intracellular levels of the antigen called Ki-67 predict recurrence of childhood pilocytic astrocytoma after surgery, according to an article in the August issue of the Journal of Clinical Oncology.

About 40 percent of all childhood brain tumors are pilocytic astrocytomas, and roughly 1,100 children under 18 years of age are diagnosed each year in the United States. According to Daniel Bowers, MD, the study’s lead author, the new finding explains why some tumors regrow quickly after surgery whereas others do not grow to clinically apparent size again. Use of the biomarker may provide physicians with important new prognostic information.

“This finding already makes a difference in how we treat patients,” he said. He follows patients with high levels of MIB-1, an antibody that is immunoreactive with the Ki-67 antigen, closely so that he can detect any potential relapse as early as possible.

The American researchers examined cell samples from 118 patients evaluated and treated in the neuro-oncology program of a university center. Tumor cells were stained with the MIB-1 antibody. Researchers sampled the number of positive cells to determine the MIB-1 index, the percentage of positive cells positive for antibody compared with the estimated total number of cells.

Linda Margraf, MD, the study’s senior author, said that patients with more than 2 percent antibody-positive cells had an increased risk of recurrence or regrowth.

Margraf said that the test, although time-consuming, is available and could benefit children with a history of pilocytic astrocytomas. “Most pathology labs can do it, and it is available at most major medical centers,” she said.

The next step in the research is to identify genes that are overexpressed in progressive tumors. Researchers hope to define tumors genetically and create drugs to treat the underlying carcinogenic processes.