Characteristics of Clinical Response in Patients With Chronic Myeloid Leukemia With an ABL1 In-Frame Exon 4 Deletion: A Multicenter Retrospective Study.

INTRODUCTION

In-frame Exon 4 deletion (p.L184_K274del) is a rare ABL1 splicing variant in chronic myeloid leukemia (CML), the clinical significance of which remains unclear.

METHODS

We retrospectively analyzed seven chronic-phase CML patients with this variant, identified by Sanger sequencing during routine monitoring of atypically slow molecular responses.

RESULTS

All patients achieved hematologic responses; molecular responses, although attained, were often delayed. No patient progressed to advanced phase disease during a median follow-up of 39.0 months.

CONCLUSION

Detection of this kinase-inactive variant should not, in itself, be regarded as a definitive resistance mechanism. Larger collaborative studies using quantitative methodologies are needed.

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