According to results recently presented at the 2007 annual meeting of the American Society of Clinical Oncology (ASCO), Sprycel (dasatinib) appears just as effective, if not slightly more effective, than Gleevec® (imatinib) as first-line therapy for Philadelphia chromosome-positive, chronic-phase chronic myelogenous leukemia (CML).

Sprycel is a multi-tyrosine kinase inhibitor which has demonstrated approximately 300 times more potency than Gleevec against BCR-ABL. Sprycel is currently approved for treatment of CML that is resistant to Gleevec, or for the treatment of patients with CML who cannot tolerate Gleevec. Based on its high activity in this setting, researchers from M.D. Anderson Cancer Center conducted a clinical trial to evaluating Sprycel as initial therapy among patients with Philadelphia chromosome-positive, early chronic-phase CML.  

This trial included 35 (of the 100 ultimately planned) patients with a median age of 41 years, the majority of whom had a low or intermediate Sokal score. Patients were randomized to either two 50-mg doses twice daily or a single 100-mg dose daily.  

• All 34 evaluable patients have achieved a complete hematologic response
• 31 patients have achieved a major cytogenetic response; 20 have achieved a complete cytogenetic response.
• After 3 months of therapy, complete cytogenetic responses were achieved in 77% of patients.
• After 12 months of therapy, complete cytogenetic responses were achieved in 95% of patients (only one patient did not achieve a complete cytogenetic response).
• After 12 months of therapy, major molecular responses were achieved by 27% of patients; 5% of patients achieved a complete molecular response.

Major molecular responses were achieved in 30% of patients treated with the twice-daily regimen compared to 20% of patients treated with the once-daily regimen; however, this difference did not reach statistical significance.

43% of patients required an interruption of treatment which lasted a median of 12 days. Myelosuppression, which occurred in 4 patients, was the most common reason for treatment interruption. Pleural effusion and skin rash, both occurring in 3 patients each, were the second most common side effects resulting in treatment interruptions.  

The researchers concluded that initial treatment with Sprycel for treatment of chronic-phase Philadelphia chromosome positive CML appears just as effective as Gleevec among these patients, based on historical data involving Gleevec. Given the comparable efficacy of these two agents, results from future studies may help to tease out differences between the two that could help individualize therapy. At this time, however, the duration of response, or ability to stop and start treatment with Sprycel are not known. 

Reference: Atallah E, et al. Use of Dasatinib in Patients with Previously Untreated Chronic Myelogenous Leukemia in Chronic Phase. Proceedings the American Society of Clinical Oncology Conference. Chicago/IL. 2007,  Abstract # 7005.