Doctors attending the American Society of Hematology's annual meeting in San Francisco, California, say the pill, Glivec, could give new hope to victims of chronic myelogenous leukemia -- known by the initials CML.
Glivec is also being studied for its effect on breast and brain tumors.
"This drug is the most significant development in oncology so far," said Dr. Moshe Talpaz of the M.D. Anderson Cancer Center in Houston, Texas.
CML strikes 100,000 people annually in the United States and Europe.
The experimental drug, previously known as STI-571, is manufactured by Novartis Pharma AG, a global pharmaceutical firm based in Basel, Switzerland.
Researchers say the drug could be on the market in one or two years.
As part of pharmaceutical tests, more than 1,000 patients in six countries are now receiving Glivec.
Some of Glivec's most promising results have been seen in patients in the chronic or first phase of CML, who failed standard therapy with a drug called Interferon.
After six months of therapy with Glivec, preliminary findings showed that half of 290 patients tested were improving. They had what's known as a cytogenic remission -- a reduction in the 'Philadelphia Chromosome' which causes the disease.
'We are very encouraged'
"There is a very high likelihood that this drug has the potential for leading to a cure for chronic CML patients," said Dr. Hogop Kantarjian with the M.D. Anderson Cancer Center. "This drug has only been studied for a year and it really takes 10 years of successful treatment for something to be considered a cure, but we are very encouraged."
"The new findings are better than we had hoped," said Dr. Kantarjian. "In the past with cancer treatments, often phase one results are promising, but phase 2 results bring disappointing results. That's not the case with STI 571."
The positive results are being presented in more than 50 scientific presentations at the five-day medical conference that started December 1.
One year ago, the drug also stirred excitement when preliminary findings in 31 patients showed all had a complete normalization of their blood counts, indicating CML was in remission.
Cancer cells targeted
In traditional cancer chemotherapy, toxic drugs are used to kill cancer cells but they do it randomly so healthy cells also die.
But Glivec is designed to kill only cancer cells. It targets an enzyme found only in leukemia cells, which means patients experience minimal side effects. The most common adverse effects of the drug are described as mild to moderate and include nausea, muscle cramps, skin rash, heartburn and diarrhea.
Less than 3 per cent of patients have experienced serious side effects such as liver problems, fluid retention and hemorrhaging.
Drug also helps advanced CML victims
Another study being presented at the scientific meeting looked at more advanced cases of CML. These patients are very ill and tend to live for one to two years.
"In these patients we found a very high response rate, there was some response seen in 91 percent of the patients," said Dr. Talpaz of the M.D. Anderson Cancer Center. "Some of the patients returned to the chronic phase of the disease."
Researchers estimate about 75 percent of this group of patients will be alive after one year with this treatment.
"We did not think we would see a 91 percent response rate in patients with advanced cases of CML," said Dr. Talpaz.
Results of a large phase 3 study that will include 1,200 CML patients are expected in March.