SHORT REPORT

Derivative chromosome 9 deletions in chronic myeloid leukaemia: interpretation of atypical D-FISH pattern

T S K Wan¹, S K Ma¹, W Y Au² and L C Chan¹

¹ Department of Pathology, The University of Hong Kong, Queen Mary Hospital, Pokfulam Road, Hong Kong, PR China
² Department of Medicine, The University of Hong Kong

Correspondence to:
Correspondence to:
Dr S K Ma, Division of Haematology, Department of Pathology, The University of Hong Kong, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong, PR China;
eskma{at}hkucc.hku.hk

Background/Aims: New molecular cytogenetic techniques are increasingly applied as a routine investigative tool in haematological malignancies, both at diagnosis and subsequent monitoring. This report describes the interpretation of atypical signal patterns encountered using BCR–ABL dual colour dual fusion fluorescence in situ hybridisation (D-FISH) translocation probes in chronic myeloid leukaemia (CML).

Methods: Interphase FISH experiments were carried out using BCR–ABL D-FISH probes in 46 patients with CML at diagnosis and during subsequent disease monitoring. Atypical hybridisation signal patterns were characterised by molecular cytogenetic techniques and correlated with conventional karyotyping.

Results: Two patients showed atypical interphase D-FISH patterns with one orange, one green, and one fusion (1O1G1F) signal. The presence of BCR–ABL gene fusion was documented by a dual colour single fusion (S-FISH) probe. The submicroscopic deletion of the ABL–BCR fusion gene on the derivative chromosome 9 in these cases was subsequently characterised by metaphase FISH on relocated G banded metaphases.

Conclusions: Atypical interphase D-FISH patterns should not be interpreted in isolation and should be considered in conjunction with other cytogenetic or molecular genetic investigations.

Keywords: chronic myeloid leukaemia; BCR; ABL; dual colour dual fusion fluorescence in situ hybridisation; chromosome 9 deletion; molecular cytogenetics

Abbreviations: CML, chronic myeloid leukaemia; D-FISH, dual colour dual fusion fluorescence in situ hybridisation; FISH, fluorescence in situ hybridisation; G, Giemsa; Ph, Philadelphia; S-FISH, dual colour single fusion fluorescence in situ hybridisation

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