Prognostic Significance of High FLT3 Expression Levels in Twenty-Six MDS Patients Examined at Diagnosis and during Disease Outcome.

An internal tandem duplication (ITD) or a point mutation of the FLT3 is detected in about one third of MDS patients at the time of clinical progression, but very few studies have determined whether these mutations are already present on clinical diagnosis. A high FLT3 expression is caused by both these as well as by other still undefined mutations. Therefore, we have decided to analyse the expression of the FLT3 gene by RT-PCR on clinical diagnosis and during disease outcome in twenty-six MDS patients. Our study was aimed at determining whether a high FLT3 expression was correlated with any peculiar clinico-haematological parameter, clinical evolution to AML and response to treatment.

Fourteen patients were males and twelve females; their median age was 60 years (range 36–76). According to FAB classification seven patients were classified as refractory anemia with ringed sideroblasts (RARS), fourteen as RA and five as refractory anemia with excess of blasts (RAEB). Conventional cytogenetic studies discovered a normal karyotype in twenty patients, a del(20q) in three, a del(5q) in two and a del(12p) in one. Blast cell percentage was 0–5% in twenty patients, 6–10% in four and 11–20% in two. According to IPSS fifteen patients were considered low-risk, eight intermediate-1 risk and three as intermediate-2 risk. FLT3 expression was evaluated through a relative real-time quantification approach which used SybrGreen I as DNA binding fluorescent dye. Total RNA from mononuclear cells from a patient, who harboured an ITD of the FLT3 gene and presented a high expression of the gene, was serially diluted in order to obtain a standard curve for real-time quantification. FLT3 expression was determined by the ΔΔCt method. FLT3 levels were normalized to ABL and calibrated on a normal sample. At the onset of the disease twenty-three patients showed a FLT3 expression similar to that of the normal control, while three (one RA and two RAEB) presented a two-four fold increase. In these last patients no correlation with any particular clinico-haematological feature was noted. Nine of the twenty-six patients progressed in AML after a median time of thirty-one months (range 8–86). Three of them had already presented an increased FLT3 expression on clinical diagnosis. Considering the remaining six patients, a three-seventeen fold increase of FLT3 expression was observed in two patients and a normal FLT3 expression in the other four. Time from MDS to AML evolution was 8,22,29,33,39 months for patients with a high FLT3 expression and 31,40,42 and 86 months for those with a normal FLT3 expression. Three of the five patients with a high FLT3 expression were given different courses of intensive chemotherapy. One of them, who never responded to chemotherapy, maintained a constantly high FLT3 expression, the other two, who achieved complete remission, showed a normalization of FLT3 expression. However both of these two responsive patients again presented a six-eight fold increase of FLT3 expression on relapse.

In conclusion, a high FLT3 expression i) may be observed on clinical diagnosis in about 11,5% of MDS patients, ii) does not associate with any peculiar clinico-haematological finding, iii) frequently appears at the time of AML evolution since it was detected in two of our six patients who showed a normal FLT3 expression on clinical diagnosis but a high expression on relapse.