Human Telomerase Reverse Transcriptase (hTERT): A New Potential Prognostic Marker in AML?

Abstract 4790

Our study, was aimed at establishing whether hTERT expression correlates with karyotype complexity, molecular findings, clinico-biological parameters, and has any prognostic impact. The 90 de novo AML patients included within the present study came at our Institution within a three-years period (January 2008 – January 2011). They were 37 females and 53 males with a median age of 59 years (range 18–84). According to WHO classification 4 (4.4%) patients were classified as M0/M1, 43 (47.8%) as M2, 37 (41.1%) as M4, 5 (5.5%) as M5 and one as M6. Fifty-one (56.6%) presented a normal karyotype (NK) and 39 (43.45) a CK (≥3 defects); the two patient groups were comparable by age. An internal tandem duplication (ITD) of the FLT3 gene and a NPM1 mutation were revealed in 12 and 2 chromosomally normal patients. No CK presented a FLT3 ITD. All patients received standard induction chemotherapy followed by two courses of consolidation treatment. At the time of the study 38 patients achieved a complete remission (CR) and 36 died. Median follow-up was 19.1 months (range: 11.5–58.6). hTERT expression was determined on patients bone marrow samples and 26 unselected cord blood (CB) cells (internal controls) by real-time reverse transcriptase PCR with SYBR Green I. Primers, designed using BLAST (http//www.ncbi.nlm.nih.gov/BLAST/), were complementary to hTERT exon 13 and allowed amplification of all transcripts coding for TA active and inactive forms. hTERT expression was normalized against the ABL gene and relative quantification was made using the 2^ΔΔCt method. At clinical diagnosis NK and CK presented a significantly different median hTERT expression: 1.91 (range 0.9–5.54) versus 5.19 (range 2.37–21.1) p<0.001. This difference remained significant even when age was considered. Interestingly, the median hTERT expression of NKs was significantly different from that of CB cells (1.91 versus 10.31, p<0.0001) which median hTERT expression was similar to that of CKs. In order to perform statistical analysis, hTERT expression was dichotomized using the median value (3.12; 95% Confidence Intervals: 2.14–4.85) as the cut-off value. A low hTERT expression (<3.12, LE) was associated with a median white blood cell count significantly higher than that associated with a high hTERT expression (≥3.12, HE): 12.0×10⁹/l (range: 7.3–58.0) versus 9.9×10⁹/l (range 2.8–18.3) (p=0.02). No significant difference for other clinical parameters was noted. A high hTERT expression was never associated with a FLT3 ITD mutation. Although the median OS of patients with LE and HE was 17.4 months (range: 7.7- not reached) versus 10.2 months (4.2–22.9), a long-rank test revealed a only trend toward a statistical significant difference (p=0.09). Patients with a high hTERT expression showed a HR=1.6 (95% CI=0.9–2.8). When the analysis was adjusted for karyotype, this variable maintained its statistical power (p<0.001). CR was achieved in 22 patients with LE versus 16 patients with HE: median time to CR achievement was 1.3 months (range 1.1–3.0) versus 3.6 months (range 1.5–37.3). When a long-rank test was applied, a significant difference between LE and HE groups became apparent (p<0.02). Instead, no significant difference between these two patient groups was noted when CR duration and relapse were considered. In conclusion, i) the significant correlation between a high hTERT expression and CKs may account for AML genetic instability which may prevent leukemic cells from replicative senescence and may promote clonal selection; ii) a high hTERT expression may be an additional prognostic marker as it significantly lowers the probability of CR achievement and determines an OS and DFS shorter, although not significantly shorter, than those associated with low hTERT expression.