Complex translocations, simple variant translocations and Ph-negative cases in chronic myelogenous leukaemia.

A proportion of cases of chronic myelogenous leukaemia (CML) has been described either (1) with a variant translocation, or (2) without the apparent involvement of both 9q34 and 22q11 (Ph-negative CML). All variant translocations have been further demonstrated to be complex implicating 9q34,22q11, plus another breakpoint on a variable chromosome. Complex translocations may be due to two successive events. Some of the breakpoints on the variable chromosome appear to be recurrent, and these remain to be studied for prognostic significance. Ph-negative CML comprises (1) cases of submicroscopic (hidden) insertion of 9q34-ABL within 22q11-BCR, and (2) cases without BCR-ABL rearrangement. We propose this last category to be called "CML-like disease", not to be confused anymore with true CML, and consequently to be studied as a separate entity.