Tyrosine Kinase FLT3 and C-KIT Receptor Expression in Patients with Myelodysplastic Syndromes – A Preliminary Study

Abstract 4620

Myelodysplastic syndrome (MDS) is a clonal hematopoietic stem cell disorder characterized by dyshematopoiesis and high susceptibility to acute myeloid leukemia.

Deregulated epigenetic mechanisms are likely involved in the pathogenesis of MDS. Gene silencing through aberrant CpG island methylation is the most extensively analyzed epigenetic event in human tumorigenesis and has huge diagnostic and prognostic potential. Aberrant methylation of gene promoter region is responsible for inappropriate gene silencing, and it has been associated to initiation and progression of cancer. However, in the MDS disease process, more and more gene dysfunction has been related with the pathogenesis. FLT3 and c-KIT are important members of the receptor tyrosine kinase family that are overexpress or dysexpress in many malignant hematologic diseases. However, little is known about the distribution and the role of these proteins in MDS.

The study is to investigate the role of receptor tyrosine kinase FLT3 and c-KIT expression in patients with myelodysplastic syndromes (MDS) and their clinical implication.

We have at moment examined c-kit protein (CD117) expression by flow cytometry, in CD34 bone marrow cells collected at diagnosis of 12 patients with de novo MDS and 5 non-neoplastic patients (controls). FLT3 mutations, in particular Internal Tandem Duplications (ITD) and the D835 mutation were analysed by PCR-RFLP. The median age was 72 years (22–89), gender M/F=5/7, WHO subtypes: RCMD (n=6), RA (n=3), RARS (n=1), AREB-2 (n=1), CMML (n=1) and IPSS: low (n=6), intermediate-1 (n=5) and intermediate-2 (n=1). None of the patients evolved to acute leukemia, with a median follow up of 24 months (7–74).

Our preliminary results show an increase in c-KIT expression in CD34 positive cells in MDS patients as compared with controls. However, the percentage of c-KIT protein expressing cells was also higher than in the controls in particular in CD34 negative cells. There was a correlation of the c-kIT protein expression with the CD34 antigen of the cells. Expression is correlated with the WHO MDS classification and with IPSS, being highest in RAEB-2 and INT2 MDS prognostic group. These results suggest that the elevated c-KIT expression could maintain the affected clone in MDS. Besides that we didn't find any FLT3 mutations in our population However further data and refinement of data analysis are needed to confirm our results and to predict clinical outcomes. The preliminary results suggest that c-KIT expression could be helpful to the pathogenesis and prognosis prediction of MDS patients.