The proto-oncogene expression varies over the course of chronic myeloid leukemia

Abstract

The chronic phase (CP) of chronic myeloid leukemia (CML) is characterized by the expression of chimeric BCR/ABL gene, extended survival, and profligate growth of maturing granulocyte stemline. The accelerated phase (AP) and blast crisis (BC) of CML are usually manifested by additionally acquired oncogene aberrations, resistance to therapy, advancing anaplasia, progressive organomegaly, and increased blast count. Abnormal expression of some proto-oncogenes may accompany or even precede AP or BC of CML. Our objective was to follow-up oncogene expression over time covering different clinical phases of CML. A total of 85 patients [44 females and 41 males; median age 51 years; range 16-75 years] were studied. At the start of the study, 29 patients were in CP, 25 in an AP, and 31 in BC. Temporal variation in expression (percentage positivity per 1000 analyzed cells) of c-kit, c-myc, H-Ras, cyclin A1, p53, bcl-2 and VEGF oncogenic proteins in CP, AP, and BC of CML was studied by immunohistochemical procedures. This was then correlated with parameters of clinical disease (organomegaly, duration of CP, AP, and BC) and laboratory (Hb, WBC and platelet counts, and the percentage of blasts) data. The level of c-kit expression differed significantly over the course of disease (x(2), p = 0 x 025). Antiapoptotic bcl-2 protein increased significantly with the progression of CML (x(2), p = 0 x 005). The expression of c-myc was most pronounced in the AP (Anova, p = 0 x 033) and then tended to decline. There was no significant difference in the level of expression of H-Ras, cyclin A1 and p53 over the course of disease. The expression of VEGF protein was most pronounced in the AP (Anova, p = 0 x 033) and it was inversely correlated with degree of splenomegaly (Pearson, r = -0 x 400, p = 0 x 011) and overall survival (log rank, p = 0,042).

Conclusion: The changes in oncogene expression, assessed by immunohistochemical approach over the course of CML may have clinical relevance in deciding on and timing of therapy. Temporal distribution of changes in oncoprotein expression in CML requires further study at the molecular level.