[Complex molecular monitoring of chronic myeloid leukemia]

The authors have monitored the treatment of chronic myeloid leukaemia by simultaneous investigation of the residual tumour mass as well as the expression of the bcr-abl chimera. The first parameter was obtained by calculating the bcr-abl rearrangement positive cells as determined by fluorescent in situ hybridisation (FISH). The other value was determined by a quantitative (competitive) reverse transcription polymerase chain reaction (Q-RT-PCR). To avoid any inaccuracy associated with the variable yield of RNA isolation and reverse transcription, respectively, the amount of chimera mRNA was related to that of abl 2-3 transcript as internal control. The threshold for the sensitivity of the Q-RT-PCR procedure was 16 bcr-abl mRNA molecule/microgram RNA. The lowest relative concentration was represented by detecting 1 bcr-abl mRNA molecule out of 12,600 abl 2-3 transcripts. The analysis of peripheral blood samples of 33 untreated patients indicated that the amount of chimera mRNA changes between 80 and 1,000,000 molecules per microgram RNA and this parameter correlated hardly (r = -44) with the tumour load. Data from blood samples of 48 treated patients indicated that this four order of magnitude difference in the expression persists in that patient population which exhibited on average major cytogenetic and also in those without any cytogenetic response. In the individual patients not only correlated changes of residual tumour mass and chimera expression, but mainly independent changes of these two parameters were observed.