WASHINGTON, April 10 (Reuters) - Stem cells -- master cells that are used to renew brain cells, blood cells and other cells -- might be used to treat both cancer and spinal cord injuries, researchers will report this week.

Two reports presented at a meeting of neurosurgeons suggest that the cells can home in on damaged tissue and replace it.

The studies were done in animals and are very preliminary, but add to the growing list of potential uses for stem cells, which scientists are just learning how to harness.

Dr. Karen Aboody and colleagues at Children's Hospital in Boston tested stem cells on mice with brain tumors.

"Malignant brain tumors remain virtually untreatable and are inevitably lethal, despite surgical excision and radio- and chemotherapy," Aboody said in a statement.

Her team wanted to see if neural stem cells, which can become any one of a number of different nerve cells, could be used to home in on and target the tumors.

Other studies have shown that neural stem cells can move through the brain, if they are grown in special cultures that program them correctly.

A few weeks after they were injected into the brains of the mice, the stem cells seemed to have migrated to the tumors, Aboody told a meeting of the American Association of Neurological Surgeons in San Francisco.

When the neural stem cells were injected into a distant site from the main tumor mass, the cells also moved to the tumor, suggesting they were somehow attracted to the tumor or the surrounding brain damage it causes.

The researchers said stem cells might be used to carry genes that could help stop the tumors, or perhaps even kill them. "These early studies suggest that neural stem cells can serve as vehicles for gene delivery in the adult brain," Aboody said. They might also be used to carry cancer drugs right to where they are needed.

"One of the problems in treating malignant brain tumors is that these lesions are not confined," Dr. Joseph Piepmeier, Chair of the American Association of Neurological Surgeons, said in a statement.

"They infiltrate into the surrounding brain tissue. Consequently, novel ideas are needed to enable neurosurgeons to deliver therapy that can reach these isolated tumor cells."

A second study presented at the same meeting used embryonic stem cells -- which are taken from extremely early embryos left over from infertility treatments -- to try and treat spinal cord injuries.

Embryonic stem cells have the ability to become any kind of cell in the body at all, but they require special culturing and handling and scientists are just learning how to do this.

Dr. Todd Stewart of Washington University School of Medicine in St. Louis and colleagues injured the spinal cords of 40 rats. Nine days later, they injected stem cells into the spinal cords of half the rats.

Within three weeks, the rats who got the injections were clearly able to move their back legs better than the rats who were not treated, Stewart said.

"In a spinal cord injury, the communicating nerve cell impulses are blocked or the nerves are severed, preventing brain signals that control arm and leg movement from traveling beyond the point of injury to the body, and vice versa," Stewart said.

"This approach to stem cell therapy represents a potential means for repairing that communication block and reversing some of the damage from spinal cord injuries."

Scientists think that perhaps stem cells respond to chemical signals sent out by dying or damaged cells, and can somehow program themselves to replace such cells.