Trisomy 12 in B-cell chronic lymphocytic leukemia: interphase study by in situ hybridization in 75 patients

Trisomy 12 is the most common cytogenetic abnormality in chronic lymphocytic leukaemia (CLL) and may be a prognostic indicator. In the present study, fluorescence in situ hybridization (FISH) is shown to be a method of choice for detection of trisomy 12 in interphase cells. Seventy-five cases of B-cell CLL were analysed with a chromosome 12 specific alpha satellite DNA probe and results compared with those from cytogenetic analysis. FISH showed the three hybridization spots characteristic of trisomy 12 in 32/75 patients (42.6%). Sixty-three patients were also studied by conventional cytogenetics: failure in 7 cases, normal karyotype in 28, trisomy 12 in 9 (14.3%) and in 19 cases abnormalities other than trisomy 12. In these same 63 patients, trisomy 12 was detected on 29 occasions by FISH (46%): in one case of failure by cytogenetic analysis, in 9 cases thought to have a normal karyotype, in 10 cases carrying abnormalities other than trisomy 12 and in all 9 cases showing trisomy 12 by conventional cytogenetic investigation. Correlation between trisomy 12 and the three stages of the Binet classification indicated an increasing proportion of trisomy 12 from stage A to stage C. It is concluded that fluorescence in situ hybridization is a powerful and sensitive technique for detection of trisomy 12 in CLL and although more cases will be required to confirm a correlation between the incidence of trisomy 12 and the stage of the disease, this link could be important from a prognostic point of view.