Correlation between the Type of BCR-ABL Transcripts and Blood Cell Counts in Chronic Myeloid Leukemia—A Possible Influence of MDR1 Gene Expression

The impact of BCR-ABL mRNA type (b3a2 vs. b2a2) on chronic myeloid leukemia (CML) phenotype is still a subject of controversies. We searched for a correlation between the BCR-ABL transcripts type and CML patients’ characteristics, including MDR1 gene expression. Ninety-eight untreated chronic phase CML patients were studied. The type of BCR-ABL fusion transcripts and MDR1 gene expression were determined by reverse transcriptase polymerase chain reaction. B3a2 and b2a2 transcripts were found in 53 [54%] and 44 [45%] patients, respectively. One patient co-expressed b3a2/b2a2 and was excluded from analysis. The only difference in the clinical characteristics between the two groups was the platelets count, that was higher in b3a2⁽⁺⁾ patients [791.3 ± 441.3 × 10⁹/L vs. 440.4 ± 283.4 × 10⁹/L in b2a2⁽⁺⁾; p = 0.007]. MDR1 over-expression [MDR1⁽⁺⁾] was observed in 48 patients (49.5%), more frequently in older patients >60 years [71% (24/34) vs. 38% (24/63) in younger; p = 0.008], and was associated with a lower white blood cells (WBC) count [105.5 ± 79.8 × 10⁹/L vs. 143.6 ± 96.5 × 10⁹/L in MDR1^(–) cases; p = 0.047]. On performing the analysis only within the MDR1⁽⁺⁾ group, the b3a2⁽⁺⁾ cases were characterized with a significantly higher platelets count [908.7 ± 470.1 × 10⁹/L vs. 472.9 ± 356.1 × 10⁹/L; p = 0.006] and a lower WBC count [85.4 ± 61.2 × 10⁹/L vs. 130 ± 93.9 × 10⁹/L; p = 0.004) compared to b2a2⁽⁺⁾ patients. No similar differences were found between b3a2⁽⁺⁾ and b2a2⁽⁺⁾ groups with normal MDR1 levels. These results indicate that the type of BCR-ABL transcripts correlates with the hematological parameters of CML, however only in the subgroup of patients characterized by MDR1 over-expression.