Transformation of CLL to ALL used to be regularly reported. The first report mentioned blast cells with surface immunoglobulin, which would be uncharacteristic for classical ALL.59 One of the two cases in this study had surface IgMK, with rheumatoid factor activity on both lymphocytes and lymphoblasts, and it now seems more likely that this and subsequent cases represent either a Richter-like transformation of CLL with peripheral blood spillover of the high-grade lymphoma cells, or a similar high-grade transformation of a different B-cell lymphoma with a superficial resemblance to CLL.
In at least one of the reported cases, the CD5 antigen was retained during the blastic phase,60 which raises the possibility of a blastic version of mantle cell lymphoma occurring in a patient with the type of mantle cell lymphoma that closely resembles CLL,41 and this seems certainly to be the explanation for the most recent case report where both the small-cell version and the blastic version had the t(11;14) translocation.61 However, in another case the blasts were shown to be terminal deoxynucleotidyl transferase positive,62 and in this and other cases the blast cells had the characteristics of ALL.63 In such cases, however, it has not been established that the ALL belongs to the same clone as the CLL.
There is no convincing evidence that CLL ever transforms into ALL.
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