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Imatinib Alone Not a Long-Term Cure for Chronic Myeloid Leukemia: Presented at ASH

By Mike Fillon

ATLANTA, GA -- December 15, 2005 -- When discontinuation of imatinib therapy in patients with chronic myeloid leukemia (CML) inevitably results in a rapid loss of response, the cure is unlikely to be imatinib monotherapy, researchers said here at the 47^th Annual Meeting of the American Society of Hematology (ASH).

Previous studies concerning imatinib over the past 5 years have defined its role as an effective first-line therapy for CML patients with complete response (CP).

However, Monica Bocchia, MD, associate professor, department of hematology, University of Siena, Siena, Italy, in a presentation on December 12^th, noted that her research team also noted that when the drug was discontinued, so did the patients' recovery.

In her study, her research team looked at the antitumor effect of a vaccine (CMLVAX100) targeting the BCR-ABL genes and found that it reduced any remaining tumor in some patients with CML who had reached a maximum response to imatinib.

After a median time of 24 months of imatinib treatment, a group of 21 patients showing different degrees of persistent residual disease started vaccinations with CMLVAX100. Eight of the 21 patients presented with molecular disease, 10 had residual cytogenetic disease (range 2-45% of Ph+ metaphases), and 3 had only hematological response (100% of Ph+ metaphases).

No improvement of their residual disease was documented for a median of 12 months (range 6-24) before starting initiating the vaccinations.

Vaccine treatment plans included 6 vaccinations at 2-week intervals. In patients who responded to treatment, additional boosts of vaccine were provided every 4 to 6 months.

To date, 18 of the 21 patients have completed the immunization regimen, 8 of whom received 4 additional boosts of vaccine.

After six vaccinations, 6 patients with persisting, progressing disease reached a complete response, with 3 of them achieving an undetectable level of BCR-ABL transcript.

In addition, 3 patients starting vaccinations with persistent molecular disease further reduced their BCR-ABL level, with 1 reaching molecular negativity. This suggests that CMLVAX100 works effectively with imatinib in CML-CP patients with persistent minimal residual disease.

Of the 8 patients who underwent 4 additional boosts of vaccine, 1 reached a complete molecular response, 5 maintained the response obtained after immunization, and 2 patients (who previously achieved an undetectable level of BCR-ABL transcript) lost the complete molecular response (CMR), but maintained complete cytogenetic response.

This finding suggests that while beneficial, a 6-month interval between boosts could be too long to maintain efficient immune control on residual leukemia cells, Dr. Bocchia noted.

Although the number of patients who participated in the trial is small, this is a still an important study, she added.

"Researchers have been attempting to develop cancer vaccines for decades, and results in CML patients are a very encouraging step forward," Dr. Bocchia concluded.


[Presentation title: Control of Residual Disease in Imatinib Treated Chronic Myeloid Leukemia Patients With Peptide Vaccinations: 2 Years Follow up of CMLVAX100 Trial. Abstract 167]

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