Targeted Therapy for Leukemia May Prove a Breakthrough
Based on earlier research, Druker and his team knew that the molecular pathway that leads to CML is based on an enzyme called BCR-ABL found in cancer cells. They tested several potential blockers of this enzyme and found the most promising is STI571, which will be called Glivec if it is approved by the FDA and marketed later this year by Novartis.
Just over two years ago, Druker and his team started testing this new drug on CML patients who had not responded to other therapy.
The results so far have been dramatic. Not only is the drug safe (side effects include only mild cases of nausea, muscle cramps, and eye puffiness), but it is also extremely effective, especially when first given during the early stage of the disease.
So far, relapse rates have only been high in those starting the drug later in the disease process, but there is some hope that combining STI571 with other therapies will control these relapses. Druker presented his award-winning findings last week in New Orleans at the annual meeting of the American Association for Cancer Research.
"For CML, this is a major breakthrough, and it validates the paradigm in cancer research of targeting the specific abnormalities that drive the course of cancer instead of [using] chemotherapy, which kills normal cells as well as the [cancer] cells," Druker tells WebMD. "Therapies coming in the future are just going to attack the cancer cells."
STI571 also blocks molecular pathways known to be involved in other cancers, and other research teams are currently testing its effectiveness in these other cancers. Druker has tried the drug in another form of leukemia that typically affects children and adolescents, called acute lymphoblastic leukemia, or ALL, with good results.
A team of Finnish researchers led by Heikki Joensuu, MD, PhD, a specialist in oncology and head of the department of oncology at Helsinki University Central Hospital in Finland, has shown the drug is effective in a woman with a gastrointestinal tumor that had started to spread to the liver. STI571 shrank the tumors even though this patient had not responded to any other therapy. Studies on STI571 for CML, ALL, and stomach cancer are published in the April 5 issue of The New England Journal of Medicine.
John M. Goldman, MD, co-wrote an editorial that accompanied these studies. He considers STI571 a real breakthrough in the treatment of CML because it is far more effective than currently available therapy and has far fewer side effects, at least in the short term.
Because the drug has only been used for a couple of years, however, there is no proof that its positive effects are long lasting or that it really lengthens people's lives. Researchers, therefore, must continue to compare STI571 to available therapies for CML, says Goldman. And, he notes, younger, healthier patients might do best with a more radical therapy, like bone marrow transplantation, that is more dangerous but is also known to cure CML when it is successful. Goldman is from the Imperial College School of Medicine in London.