Experimental drug fights rare leukemia

(CNN) - An experimental cancer therapy is showing promise against a rare form of leukemia, researchers reported Wednesday.

Scientists at the National Cancer Institute have been conducting early trials on a drug called BL22 for the treatment of hairy cell leukemia. Their work is published in Thursday's issue of the New England Journal of Medicine.

Hairy cell leukemia causes the spleen to swell and prevents the bone marrow from producing enough infection-fighting white blood cells. About 1,000 new cases are reported each year in the United States.

The standard treatment is chemotherapy, but not all patients respond.

The NCI researchers administered the drug to 16 patients who had not been helped by chemotherapy. Eleven of them went into full remission -- doctors found no cancer cells or only very few cancer cells in their bodies. Two patients went into partial remission.

RESOURCES Learn more about leukemia from the National Cancer Institute

"We were totally amazed to see the results," said Dr. Ira Pastan, one of the study authors, "amazed and excited because this is a phase one trial where we started a very low dose and mainly looked for safety of the drug. But as we just increased a little bit we found patients who were beginning to respond and eventually a large fraction of the patients we treated responded."

Jeffrey Desind, who was diagnosed with hairy cell leukemia six years ago, was one of those patients.

"I think the doctors had me buried six feet under, and I'm walking around and every day it's another day," he said.

Targets only cancer cells

The drug works by attaching itself to the surface of the leukemia cell. It then sends in a toxin that kills the cell. Like many new cancer drugs, BL22 targets only the cancer cells, unlike radiation and chemotherapy which kill the good cells along with the bad.

Although some of the patients experienced side effects like nausea, swelling and even a more serious blood reaction that can affect the kidneys, the doctors were able to treat and reverse the negative reactions.

"One of the advantages of this therapy is it doesn't have the prolonged side effects such as bone marrow suppression, so we frequently re-treat patients," Pastan explained.

But the researchers warned that even with repeat treatment, BL22 may not work over the long term. So far in these initial trials, the longest it has worked is two years.

"In cancer treatments we rarely speak of cures," Pastan said.

However, scientists are hopeful that the principle behind BL22 can be applied to drugs to treat other types of cancer.

CNN Medical correspondent Elizabeth Cohen contributed to this report.