High Prognostic Value of a 3-Genes Molecular Score in Non-High Risk Acute Promyelocytic Leukemia Treated with AIDA 2000 Protocol: A Retrospective Study from a Regional Register

BACKGROUND AND AIMS

Non high risk acute promyelocytic leukemia (APL) patients, as defined by WBC count at diagnosis, have nowadays a very good prognosis when treated with ATRA plus chemotherapy based protocols, with high rate of complete molecular remission after consolidation therapy. However, a small proportion of patients (roughly 10-15%) will eventually relapse, despite the achievement of molecular CR.

In the past years, some groups showed that relapse risk could be predicted by testing for some gene alterations,  such as FLT3-ITD, or by break point cluster region (BCR) analysis. However, those results were not  confirmed in prospective  trials.

We retrospectively applied a simple 3 gene based molecular panel to low-intermediate risk acute promyelocytic patients, alongside with BCR analysis, in order to develop a risk score.

MATERIALS AND METHODS

Fifty-nine low/intermediate risk APL patients, treated with the Italian age-adapted AIDA protocol from January 1^st 2004 to December 31^st 2014 in our center were retrospectively included in this study. Median age was 47 years (range 19-88), 16 patients were older than 60 years (27%).

BCR analysis was available in all patients, 41 patients showed BCR1/2, whereas 18 patients had BCR3 (30%).

Molecular profile included determination of  FLT3-ITD mutation, WT1 and BAALC gene expression levels and was available in 38/59 patients (64%); bone marrow sample of diagnosis is available for all other 21 patients for further analysis. Cut-off values for WT1 (20000/abl x 10⁴) and BAALC (450/abl x 10⁴) were arbitrarily chosen after pre-analysis and comparison  with our published data.

Five patients had FLT3-ITD mutation (13%), 18 (45%) patients had higher WT1 expression levels and BAALC was overexpressed in 9 (24%) patients.

Pre-analysis showed that FLT3-ITD, low WT1 levels, high BAALC levels but not the presence of BCR3 were associated with higher relapse risk. A molecular score including those 3 genes was built: 16 patients had no risk factors (42%), 17 patients had one risk factor (45%), 5 had two risk factors (13%).

RESULTS

Fifty-four patients survived induction, all of them achieved CR, in 52 PML/RARα transcript was undetectable  after last consolidation therapy. The two patients with molecular persistence of disease received further therapy and then achieved molecular CR. Nine patients (15%) relapsed after a median follow-up of 56 months, 45 patients are alive at the time of analysis (76%). Relapse risk was influenced only by the presence of at least one molecular risk factor (p<0.05), whereas age at diagnosis older than 60 years had only a borderline impact (p=0.105); none of the molecular alterations reached statistical significance if taken alone.

Disease free survival (DFS) duration was significantly higher in patients who had none of the molecular risk factor, when compared to patients with at least one (3-years DFS of 100% and 70.8%, respectively, p<0.05, Figure 1). Younger patients had also a longer DFS, with a 3-years DFS of 90.7% and 72% for patients younger or older than 60 years, respectively (p<0.03).

Overall survival (OS) analysis led to similar results: patients with no molecular risk factors had a very good outcome when compared to patients with at least one alteration (3-years OS of 100% and 71.5%, respectively, p<0.03). Survival  was also influenced by age at diagnosis, as younger patients did significantly better, with 3-years OS of 90% (p<0.05).

Again, none of the molecular alterations, if taken alone, had a significant impact on DFS or OS.

CONCLUSIONS

Even in our small cohort, molecular profile could identify a subset of low-intermediate APL patients at higher risk of relapse, who may take benefit from an intensified consolidation therapy, as it is currently applied to high risk patients defined by WBC at diagnosis.

Fig. 1: DFS according to molecular risk score