Chronic myelogenous leukemia in chronic phase

Opinion statement

Chronic myelogenous leukemia (CML) is a clonal myeloproliferative disorder characterized by genomic instability leading to its inevitable clinical evolution from an easily controlled chronic phase to a terminal blastic phase. The molecular abnormality responsible for this disease—BCR-ABL—and the critical biochemical aberrations resulting from it have been studied in depth. These discoveries have led to the development of a molecule, STI571, that specifically inhibits the abnormal kinase enzymatic activity exhibited by BCR-ABL. Early results of clinical trials using STI571 have shown responses even in blast crisis. There has also been striking hematologic and cytogenetic remission rates in patients with advanced chronic phase disease, with very little toxicity. It is our opinion that this molecule will revolutionize the treatment of CML. Furthermore, the path leading to its discovery will become a paradigm for cancer therapeutics.

At the time of this writing, STI571 remains investigational (although it is widely believed that it will be approved for clinical use in the United States this year [2001]). Although suggested therapy for a disease does not generally incorporate medications that are still investigational, in this case, the impact of a still investigational agent cannot be ignored. The current data suggest that STI571 will be the treatment of choice for patients with advanced or resistant chronic phase. To date, STI571 has not been studied adequately in untreated CML patients. Even so, it is our feeling that, based on its compelling success in patients with interferon-refractory and advanced disease and on its benign side effect profile, it will quickly become the front-line therapy for CML once it becomes available. Despite the ease of administration of STI571, patients should continue to be encouraged to participate in clinical studies so that several vital issues can be resolved: 1) the percentage of untreated CML patients who will eventually develop molecular remissions; 2) the proportion of patients in whom resistance to STI571 will emerge; 3) the optimum length of treatment; and 4) the impact on survival. Because interferon-alfa can also result in cytogenetic remissions, albeit in a small percent (less than 20%) of early chronic phase patients, it seems reasonable to suggest that patients who do not attain cytogenetic/molecular remissions with STI571 alone be treated with a combination of STI571 and interferon-alfa. Patients who are resistant to STI571 with or without interferon-alfa should undergo allogeneic hematopoietic cell transplant. Salvage therapy after transplant may include donor lymphocyte infusions, interferonalfa, additional transplant, and perhaps STI571. Medications such as hydroxyurea appear destined to play a very limited role in CML. They may be used in the palliative treatment of older STI571-resistant patients or those without a transplant donor, although these patients may be best served by being considered for clinical trials of molecules, such as polyethylene glycol-interferon-alfa, on other novel agents.