BCR-ABL Fluctuation Analysis in Chronic Phase Chronic Myeloid Leukemia (CP-CML) Patients with MR 4.5

Introduction: Imatinibe, a target tyrosine kinase inhibitor, have revolutionized CP-CML treatment. Considering that it is being discussed imatinibe treatment interruption in patients with MR ≥ 4.5 lasting two years or more, we believe to be important to establish predictors of major molecular response (MMR) loss. Fluctuations in BCR-ABL transcripts are being advocated to be able to predict MMR loss, although the real impact of small fluctuations among patients with in MR ≥ 4.5 is uncertain.

Objective: Correlate BCR-ABL fluctuations and MMR loss in patients considered to be in MR ≥ 4.5, as well as to recognize possible factors associated with these small fluctuations.

Methods: We conducted a retrospective analysis in CP-CML patients receiving imatinibe (as first or second treatment line) that achieved MR ≥ 4.5 (defined as a 4.5 log reduction on an international scale) and surveyed for BCR-ABL fluctuations. We considered a fluctuation to be a rise of at least 0.5 log of BCR-ABL transcripts. Treatment interruptions were considered only when imatinibe was not taken for 15 or more consecutive days. The presence of comorbities was evaluated by applying the Charlson Index.

Results: Fifty-eight patients were evaluated between with a median follow-up 7 years. Fifty-five percent were men and 28 were women, with a median age of 46 (18 - 93) years-old, most of the patients were older than 60 yo (75,9%). Among 32 patients evaluated by the Sokal risk score 97,5% were estimated to be low or intermediate. Twenty six patients presented at least one fluctuation. Regarding the number of fluctuations per patient, 18 presented only 1 fluctuation, 5 presented 2 fluctuations and 3 patients presented 3 fluctuations. Among those patients with at least one fluctuation 3 (11%) presented MMR loss, while there was none among patients without documented fluctuations (p=0,15). Among these three patients considered to have MMR loss, two presented fluctuations that reached MR 3.0, while the other patient presented a history of long treatment suspension. More patients that interrupted treatment presented BCR-ABL fluctuations, although this difference was not statically significant (78% vs 50% p=0,11).

Conclusion: Small fluctuations among patients with MR ≥ 4.5 didn't seem to correlate with MMR loss, however we do believe that our population is underpowered to rule out this difference. We considered that it very interesting that patients which reached MR 3.0 presented MMR loss (considering that the other patient had to abandon treatment during pregnancy).