Cancer cells remain after tumor removal.

Primary tumors that arise in the brain will appear in 17,200 Americans in 1995 and kill 13,300, the American Cancer Society estimates. The most common are gliomas, which develop from the glial cells that protect and nourish neurons. The most malignant glioma accounts for 30% of all primary brain tumors. Patients rarely live more than two years after a diagnosis of malignant glioma.

Although glioma cells do not metastasize to other parts of the body, they do leave the tumor. So, when a tumor is removed by surgery or radiotherapy, millions of cells already have found their way to other parts of the brain. These cells remain behind, causing death from generalized brain dysfunction. By the time you find a tumor, the cat is out of the bag," notes Daniel L. Silbergeld, assistant professor of neurological surgery and anatomy and neurobiology, Washington University School of Medicine. "The real problem is to understand the invading cells better so we can design therapies to kill those cells. That means taking the cells out of the brain and taking a closer look at them."

Using tumor specimens obtained during surgery, he established human glioma cultures and monitored the amoeba-like cells as they wandered over the surfaces of plastic dishes. He was surprised to find that the cells traveled more than an inch in four days-600 times their length. The most mobile ones came from patients with the most malignant brain tumors. "This supports the idea that the degree of malignancy of a brain tumor relates to the ability of its cells to invade other parts of the brain."

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