Trisomy 12 is a Rare Event in Cases of CLL with Typical Immunophenotype and Morphology

131 patients with lymphoproliferative disorders were classified as having typical Chromic Lymphocytic Leukaemia [CLL], atypical CLL, Chromic Lymphocytic Leukaemia/Prolymphocytic Leukaemia [CLL/PL] or Non-Hodgkin's Lymphoma [NHL] using immunophenotyping and morphology. The incidence of trisomy 12 (+12) in each of the groups was ascertained using fluorescent in situ hybridization. Trisomy 12 was found to be rare in the typical CLL group (<3%) and more common in the atypical CLL (22%), CLL/PL (40%) and NHL (43%) categories. The low incidence of +12 in the typical CLL group is most likely due to our adherence to strict inclusion criteria to ensure other similar lymphoproliferative disorders, with a high incidence of +12, were excluded. This approach leads to more homogeneous disease categories and consequently may help to resolve issues such as the impact on survival of +12 in CLL.