Tree bark might treat rare eye cancer

An extract from the bark of a South American tree might lead to better treatments for a rare but deadly childhood eye cancer called retinoblastoma, U.S. researchers reported Friday.

Retinoblastoma affects 1 in 15,000 children, causing about 3 percent of all cancers in children. It forms when developing cells in the retina — the eye’s main light sensor — go haywire and start reproducing out of control.

“The great majority of the cases exist in the developing world, where it is a fatal disease,” said Dr. Joan O’Brien of the University of California, San Francisco, who led the study.

The cancer usually develops in children under age 6 and kills within two to four years after diagnosis if not treated.

If detected early and treated with a combination of chemotherapy agents or radiation, 90 to 95 percent of children live. But conventional treatment has significant side effects.

Combination chemotherapy can cause hearing loss, kidney failure and leukemia. Radiation therapy, which is now less commonly used, disfigures the child.

In children who have the cancer in only one eye, the eyeball is sometimes replaced with an implant.

“We can cure them, but at cost,” said O’Brien. “It’s important to find a cheap, easily administered, nontoxic therapy.”

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Cells commit suicide
O’Brien and colleagues at UCSF wanted to see whether the tree bark extract beta-lapachone could cause the abnormal cells to commit suicide — something it has been shown to do in a number of cancer types, including breast and prostate cells.

They tested the extract in the laboratory and found that beta-lapachone significantly blocked rapid cell growth of human tumor cells and that low doses could cause damaged cells to kill themselves in a process called apoptosis, or programmed cell death.

Writing in the journal Eye, the scientists said their findings support other studies of the extract in different human cancers and may lead to an effective treatment.

“The nice thing about the agent is that it kills at very low doses and it appears to be selective to cancer,” O’Brien said.

Substances that zero in on cancer are less toxic because they do less harm to healthy cells, O’Brien said. Her lab is now testing the extract in mice with retinoblastoma to look for possible toxic side effects.