The drug thalidomide was pulled from the market in the 1950s after causing horrible birth defects.

But doctors now say a new version is a powerful tool in fighting leukemia, according to a news release from the Roswell Park Cancer Institute in Buffalo, N.Y.

Norman Zobel, a cancer patient, said he was surprised how quickly the drug worked.

"The first week of taking these pills -- I take one in the morning -- the elevated white cells depleted right away and I went back into remission again," he said.

The pill is now called lenalidomide, but it was based on the 1950s tranquilizer. Doctor say it works.

"Over half of the patients went into some kind of remission. And around 18 percent of these patients went into a complete response where we can't even detect their cancer by the most sophisticated methods that we have," said Dr. Asher Chanan-Khan.

Doctors said the drug may be so effective in battling cancer because it doesn't attack the cancer itself, but the areas around it. In fact, experts said that if they put the drugs directly on cancer cells in the lab, nothing happens.

"They really are involved in altering what we call the microenvironment, or where these cancers have to live and the normal cells that support them. These drugs seem to alter that balance and now they're no longer supporting the cancers anymore," said Dr. Kelvin Lee.

Results of two international studies investigating the drug were recently published in the New England Journal of Medicine.