Hematopathologic and cytogenetic findings in imatinib mesylate treated chronic myelogenous leukemia patients : 2 . 5 years ’ experience

Background/Aim. Imatinib mesylate, a tyrosine kinase inhibitor with specific activity against the breakpoint cluster region Abelson murine leukemia (BCR-ABL) tyrosine kinase has been developed for treatment of chronic myelogenous leukemia (CML). Its hematologic and cytogenetic effects have been evaluated in a series of clinical trials. The aim of this study was to report hematologic and cytogenetic response in CML patients during the treatment with imatinib mesylate. Methods. A total of 21 patients were treated and observed from July 2006 to December 2008. The median time from CML diagnosis was no more than 12 months, so all the patients received previous treatment with hydroxyurea for which the median time was 3 months. The patients received imatinib mesylate in an effective oral dose of 400 to 800 mg daily, which was followed with peripheral blood counts, bone marrow examination, and cytogenetic studies at 6, 12, 18 and 24 months. Results. Complete hematologic responses were reported for 19 (90.48%) of 21 patients studied. Among 19 patients who had a response, 16 (86%) did so within 3 months. The best cytogenetic response rate at any time during the study treatment with imatinib mesylate, among 14 patients in which cytogenetic response evaluated was: complete cytogenetic response in 7 (50%) patients, partial cytogenetic response in 6 (42.9%) patients and minor cytogenetic response in 1 (7.1%) patient. No patients had progressed to accelerated or blastic phase. The most frequent adverse effects that seemed to be related to treatment with imatinib mesylate were edema and musculosceletal pain; overall, most were mild. Only one patient discontinued treatment because of hematologic toxic effects. Conclusion. The results obtained in this study confirm that imatinib mesylate induces a complete hematological and cytogenetic response in a high percentage of patients with chronic-phase CML.


Introduction
Chronic myeloid leukemia (CML) is a clonal disorder in which cells of the myeloid lineage undergo massive clonal expansion.The disease progresses through three distinct phases -chronic phase, accelerated phase and blast crisisduring which the leukemic clone progressively losses its ability to differentiate.
The characteristic genetic abnormality of CML, the Philadelphia (Ph) chromosome, results from a reciprocal translocation between chromosomes 9 and 22.The molecular consequence of breakpoint cluster region-Abelson murine leukemia (BCR-ABL) gene is a generation of the fusion protein BCR-ABL, which constitutively activates tyrosine kinase, present in virtually all patients with CML.For these reasons, an inhibitor of BCR-ABL tyrosine kinase should be an effective and selective treatment for CML 1,2 .
Current therapies include drug regimens with interferon alpha, hydroxyurea, busulfan, investigational agents and allogeneic bone marrow transplantation.Interferon alpha prolongs overall survival but has considerable adverse effects.The rate of hematologic response with these second-line agents is approximately 50%, but cytogenetic responses are uncommon 3 .AlloHSCT (hematopoietic stem cell transplantation) is not a first-line treatment choice in patients with CML, instead imatinib mesylate (IM) is perferred as initial treatment.AlloHSCT or investigational treatments were recommended in case of failure, and could be considered in case of suboptimal response.AlloHSCT should be considered in all patients younger than 45-50 years, that have not achieved hematological response, that have no cytogenetic response after 6 or 12 months of treatment with imatinib mesylate, or in patients with bad cytogenetic response (Ph-chromosome > 35%), as well in patients with disease recidive.AlloHSCT could be offered to patients with low or intermediate the European Group of Blood and Marrow Transplantation (EBMT) risk score and in the case of high EBMT risk score as salvage therapy 4 .
Imatinib mesylate is a potent and selective competitive inhibitor of BCR-ABL protein tyrosine kinase.Imatinib mesylate is the first molecular target therapy for the treatment of CML.He has demonstrated significant activity in all phases of Ph positive CML.Daily doses of 400 mg or more of IM induce durable hematologic responses and high rates of cytogenetic responses in nearly all patients with chronic-phase CML, with minimal toxic effects [5][6][7] .

Methods
A total of 21 patients were observed and treated from July 2006 to December 2008.The patients were 18 years of age or older and had chronic phase, Ph-chromosome positive CML.The median age of the group was 48.67 years (range 19 to 68).
The patients received an oral dose of 400 mg of IM daily.Escalation to 800 mg of IM daily was permitted for 1 patient after 6 months and escalation to 600 mg daily was permitted for 2 patients after 24 months of treatment.A dose escalation has been required because of failure of the previous treatment with IM in dose of 400 mg daily (cytogenetic refractoriness or cytogenetic relapse).One patient discontinued treatment with the drug because of hematologic toxic effect.
The chronic phase was defined by the presence of less than 15 percent blasts in bone marrow, less than 20 percent basophiles and less than 30 percent blasts plus promyelocytes in the peripheral blood and bone marrow and a platelet count of at least 100 × 10 9 /L.A hematologic response was defined as 50 percent reduction in the white-cell count from base line, maintained for at least two weeks.A complete hematologic response was defined as a reduction in the whitecell count to less than 10 × 10 9 /L and in the platelet count to less than 450 × 10 9 /L and less than 20 percent basophiles in peripheral blood, no immature cells in peripheral blood, and disappearance of all signs and symptoms related to leukemia, including palpable splenomegaly, maintained for at least four weeks 2,8 .
Cytogenetic responses were determined by the percentage of cells in metaphase that were positive for the Ph chromosome in the bone marrow.Cytogenetic responses, based on analysis of average 20 cells in metaphase, were categorized as complete (no cells positive for the Ph chromosome), partial (1-35% of cells positive for the Ph chromosome), minor (36-95% of cells positive for the Ph chromosome) and absent (over 95% of cells positive for the Ph chromosome).Major responses were defined as complete plus partial response.Cytogenetic relapse defined as at least 65 percent Phchromosome-positive cells in metaphase or an increase of at least 30 percent from the previous study 2,8 .
A complete blood count and a differential blood count were obtained weekly for the first 4 weeks, and every 4 weeks after that, while extramedullary involvement was also evaluated by physical examination.Bone marrow morphology and cytogenetic were evaluated every 6 months.Adverse effects were evaluated at each visit and graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) 9 .

Results
The pretreatment characteristics of the patient included in the study were typical for patients with chronic-phase CML and summarized in Table 1.
Among 21 patients with CML that we followed the median time from previous treatment with hydroxyurea was 3.08 months (range 1-7 months).The median duration of treatment with IM was 12.64 months (range 5 to 30) while 47.62% of the patients were treated for at least 12 months.
Peripheral blood and bone marrow values at 6, 12, 18 and 24 months in IM treated chronic phase CML patients are detailed in Table 2.
Complete hematologic responses (CHR) were attained in 19 of 21 (90.48%)patients treated during 5 months with IM, while 16 (84%) of those reached CHR in 3 months.Cytogenetic response rates to IM therapy at 6, 12, 18 and 24 months are shown in Table 3.
Of 13 patients in whom a major cytogenetic response was achieved, 4 (30.8%)continued to have such a response as of last follow-up, whereas only 1 (7.7%) had a cytogenetic relapse.The median time to cytogenetic relapse was 24 months from the start of the therapy and 18 months from the initial achievement of a major cytogenetic response.No patient has progressed to accelerated or blastic phase and all patients are alive.Strana 805 Ćojbašić I, Mačukanović-Golubović L. Vojnosanit Pregl 2010; 67 (10): 802-806.
Imatinib was generally well tolerated.The frequency of adverse effects attributable to the drug is summarized in Table 4.The most common nonhematologic adverse effects included musculosceletal pain (23.5%), edema (17.6%), and rash and related events (11.8%).Most adverse effects were grade 1 (mild) or grade 2 (moderate).Imatinib can cause a variety of hematologic toxic effects like anaemia, neutropenia and trombocitopenia.One patient had a hematologic toxic effect at grade 3/4, platelet count of less than 50 000 per mm 3 .Daily dose was reduced to 300 mg because the patient had persisted at grade 3/4 for more than two weeks and then treatment interrupted.

Discussion
Imatinib mesylate, a selective BCR-ABL tyrosine kinase inhibitor, has revolutionized the treatment of Ph chromosome -positive chronic myelogenous leukemia.Kantarjian et al. [10][11][12] and O'Brien at al. 13 present data demonstrating that imatinib is superior to interferon alfa plus cytarabine, so it is now generally accepted that imatinib is the best initial treatment for patients newly diagnosed with chronic myeloid leukemia in chronic phase.The new agent formulated for oral administration and then termed STI571 induced cytogenetic responses, some complete, in a high proportion of patients and had limited toxicity; the maximum tolerated dose was not established, but a starting dose of 400 mg daily for adults was recommended.
We compared our results with the results of IRIS study.At phase 3 IRIS study with median follow-up of 19 months, the estimated rates of complete hematologic response (CHR) for patients treated with imatinib were 96%, major cytogenetic response (MCyR) 87% and complete cytogenetic response (CCyR) 76%.In the recently updated results of phase 3 IRIS study, it was stated that with 5 years follow-up the estimated cumulative best rates of CHR and CCyR were 98% and 87%, respectively 14,15 .In our analysis, we obtained similar findings, With median follow-up of 12 months the estimated cumulative best rates of CHR and MCyR were 90.48% and 92.9%, respectively.On the other hand, cumulative best rate of CCyR was 50%, which was lower than in IRIS sudy.
The results of our analysis, showing that 57.14% of the patients achieved a MCyR by 6 months and 50% achieved CCyR after 1 year, are similar to the results reported by Goldman et al. 15 that approximately 40% of the patients achieved a MCyR by 6 months, and 65% achieved a CCyR after 1 year of the therapy.
In this study imatinib was well-tolerated, and the most nonhematological and hematological adverse effects were grade 1 or 2 (mild or moderate), while 4.7% of patients interrupted the treatment because of trombocitopenia grade 3/4.Our results are similar to those of Kantarjian et al. 16 , showing that grade 3/4 nonhematologic toxic effects were infrequent, hematologic toxic effects were manageable, and only 2% of the patients discontinued the treatment because of drug-related adverse events.No increase in rates of serious adverse events was observed with continuous use of the drug for follow up periods, compared with earlier time points.
Our results fully support the widely accepted conclusion that the preferred initial treatment for newly diagnosed patients in chronic phase CML should involve IM.Higher doses of imatinib, alternative tyrosine kinase inhibitors such as dasatinib or nilotinib and allogeneic stem cell transplantation are implemented for suboptimal response or progression and are under clinical evaluation as frontline approaches [17][18][19] .

Conclusion
After 2.5 years of follow-up, a continuous treatment of chronic-phase CML with imatinib as initial therapy was found to induce durable responses in a high proportion of the evaluated patients.Our results confirm that imatinib is remarkably safe and well-tolerated.