High WT1 expression is an early predictor for relapse in patients with acute promyelocytic leukemia in first remission with negative PML-RARa after anthracycline-based chemotherapy: a single-center cohort study.

Wilms' tumor gene 1 (WT1) expression is a well-known predictor for relapse in acute myeloid leukemia. We monitored WT1 decrement along the treatment course to identify its significant role as a marker for residual disease in acute promyelocytic leukemia (APL) and tried to suggest its significance for relapse prediction. In this single center retrospective study, we serially measured PML-RARa and WT1 expression from 117 APL patients at diagnosis, at post-induction and post-consolidation chemotherapies, and at every 3 months after starting maintenance therapy. All 117 patients were in molecular remission after treatment of at least 2 consolidation chemotherapies. We used WT1 ProfileQuant™ kit (Ipsogen) for WT1 monitoring. High WT1 expression (>120 copies/104 ABL1) after consolidation and at early period (3 months) after maintenance therapy significantly predicted subsequent relapse. All paired PML-RARa RQ-PCR were not detected except for one sample with early relapse. Patients with high WT1 expression at 3 months after maintenance therapy (n = 40) showed a significantly higher relapse rate (30.5 vs. 6.9%, P < 0.001) and inferior disease free survival (62.8 vs. 91.4%, P < 0.001). Multivariate analysis revealed that high peak leukocyte counts at diagnosis (HR = 6.4, P < 0.001) and high WT1 expression at 3 months after maintenance therapy (HR = 7.1, P < 0.001) were significant factors for prediction of relapse. Our data showed high post-remission WT1 expression was a reliable marker for prediction of subsequent molecular relapse in APL. In this high-risk group, early intervention with ATRA ± ATO, anti-CD33 antibody therapy, and WT1-specific therapy may be used for relapse prevention. TRIAL REGISTRATION: Clinical Research Information Service (CRIS), KCT0002079.

Findings

In acute promyelocytic leukemia (APL), PML-RARa transcript is used as a marker for minimal residual disease (MRD), but the marker is not useful for pre-emptive management since its positivity directly indicates relapse. High Wilms’ tumor gene 1 (WT1) expression was related with subsequent relapse in acute myeloid leukemia, and Hecht et al. recently reported that high initial WT1 expression was associated with more relapse in APL [1-3].

We confirmed APL by chromosome analysis and PML-RARα reverse transcriptase polymerase chain reaction (RT-PCR) method. All were treated with idarubicin (12 mg/m2, days 1, 3, 5, and 7) and all-trans retinoic acid (ATRA; 45 mg/m2/day) [4, 5]. After achievement of hematological complete remission (CR), all received three courses of consolidation—first, idarubicin (7 mg/m2, days 1–4); second, mitoxantrone (10 mg/m2, days 1–4); and third, idarubicin (12 mg/m2, day 1–2)—followed by 2-year maintenance using 6-mercaptopurine (50 mg/m2/day) plus ATRA [5-7]. The molecular studies were performed at diagnosis and 1 month after chemotherapy, and every 3 months after maintenance. Quantification of PML-RARα and WT1 were performed using the real-time quantitative (RQ)-PCR methods (Real-Q PML-RARα quantification kit, Biosewoom, Korea, and WT1 ProfileQuant™ kit, Ipsogen, France) presenting a similar sensitivity of 4.5 log.

We initially identified 142 APL patients from 2009 to 2014 but finally focused on 117 patients (median age 44 years old (range 19–70 years)) who underwent at least 2 cycles of consolidation after hematological CR. All patients were in complete molecular response (CMR) at the time of enrollment (Additional file 1: Figure S1, Table 1). Relapse was identified in 16 (13.7%) patients with a median duration of 22.8 months (range, 4.3–64.0). After median follow-up of 46.0 months (range, 14.7–86.3), 4-year cumulative incidence of relapse (CIR), non-relapse mortality (NRM), disease-free survival (DFS), and overall survival (OS) rates were 16.2, 1.2, 82.6, and 92.5%, respectively. We identified that high-risk Sanz-criteria, peak leukocyte count >40.0 × 109/L, and FLT3 mutation were predictive for relapse.

Table 1

Baseline characteristics of enrolled patients

Total n = 117	Number or median value
Age, median (range)	44 (19–70)
Gender, male	70 (59.8%)
Laboratory findings at diagnosis
Leukocyte count (×109/L)	2.68 (0.4–112.0)
Leukocytes count at peak (×109/L)	16.6 (0.4–112.0)
Hemoglobin (g/dL)	8.9 (4.0–15.0)
Platelet (×109/L)	33.0 (5.0–163.0)
Lactate dehydrogenase (LDH, U/L)	692 (250–4070)
Prothrombin time (PT, %)	63.0 (35.0–101.0%)
Partial thromboplastin time (aPTT, s)	28.0 (20–45)
Fibrinogen (mg/dL)	134.0 (31.0–500.0)
Antithrombin III (%)	94.0 (49.0–150.0)
D-dimer (mg/L)	17.0 (1.0–36.0)
Sanz criteria
High	64 (54.7%)
Intermediate	19 (16.2%)
Low	34 (29.1%)
Karyotype
Normal karyotype	5 (4.3%)
t(15;17) alone	79 (67.5%)
t(15;17) with 1 additional karyotype	20 (17.1%)
t(15;17) with ≥2 additional karyotype	13 (11.1%)
PML-RARa subtype
BCR1	85 (72.6%)
BCR3	32 (27.4%)
FLT3 mutation
No FLT3 mutation	86 (73.5%)
FLT3-ITD	25 (21.4%)
FLT3-TKD	6 (5.1%)
WT1 (copies/104 ABL), median (range)
At diagnosis (n = 117)	18330 (20.0–236160.0)
Post-induction (n = 117)	63.9 (4.9–2360.0)
Post 1st consolidation (n = 117)	66.2 (1.1–2320.0)
Post 2nd consolidation (n = 117)	80.1 (1.3–2110.0)
Post 3rd consolidation (n = 117)	71.9 (10.8–808.0)
aPost-maintenance 3 months (n = 117)	70.0 (6.0–5520.0)
aPost-maintenance 1 year (n = 87)	57.5 (10.0–1630.0)
aPost-maintenance 2 year (n = 62)	54.4 (10.0–500.0)
At relapse (n = 16)	239.5 (77.1–34910.0)
Leukapheresis at initial treatment	20 (17.1%)
Differentiation syndrome	21 (17.9%)
Hematological complete response
After induction	115 (98.3%)
After 2nd induction	2 (1.7%)
Complete molecular response (CMR)
After induction	68 (58.1%)
After 2nd induction	2 (1.7%)
After 1st consolidation	42 (35.9%)
After 2nd consolidation	5 (4.3%)

Abbreviation: BCR breakpoint cluster region, FLT3 Fms-related tyrosine kinase 3, ITD internal tandem duplication, TKD tyrosine kinase domain, ABL Abelson murine leukemia viral oncogene, WT1, Wilms tumor 1, ATRA all-trans retinoic acid, AML acute myeloid leukemia

aPost-maintenance indicates the time from starting maintenance therapy

We compared the level of WT1 between relapsed and non-relapsed group during the course of treatment (Additional file 1: Figure S2) and identified that median WT1 was significantly different at post 2nd consolidation (171.5 vs. 76.3, P = 0.049), at post 3rd consolidation (156.0 vs. 67.6, P = 0.013) and at 3 months post-maintenance (162.0 vs. 59.1, P = 0.002). We found that WT1 post-maintenance 3 months was the most significant parameter for relapse prediction at the cutoff of ≥120.0 copies/104 ABL.

We calculated subsequent CIR and DFS rates in 116 patients after excluding 1 patient with early relapse. Patients with WT1 post-maintenance 3 months higher than 120.0 copies/104 ABL showed higher 4-year CIR (30.5 vs. 6.9%, P = 0.0002) and inferior 4-year DFS (62.8 vs. 91.4%, P < 0.0001) rates (Fig. 1a, b). Also in the high-risk subgroup, high WT1 post-maintenance 3 months showed higher 4-year CIR (43.3 vs. 11.1%, P < 0.0001) and inferior 4-year DFS (55.5 vs. 86.4%, P = 0.0015) rates (Fig. 1c, d). In FLT3 positive and negative subgroup, high WT1 post-maintenance 3 months showed higher 4-year CIR (51.4 vs. 0.0%, P < 0.0001 and 21.5 vs. 8.6%, P = 0.0434) and inferior 4-year DFS (46.7 vs. 100.0%, P = 0.0018 and 69.6 vs. 89.3%, P = 0.0154) rates (Fig. 1e, f).

Fig. 1

Treatment outcomes according to WT1 expression level (<120 vs. ≥120 copies/104 ABL) at 3 months post-maintenance (PM-WT1). a Four-year CIR rates. b Four-year DFS rates. c, d Four-year CIR and DFS rates according to WT1 expression level in the high-risk subgroup. e, f Four-year CIR and DFS rates according to the status of PM-WT1 and FLT3-ITD mutation

Multivariate analysis (Additional file 1: Table S1) revealed that 4-year CIR was significantly higher in patients with high peak leukocyte count (HR = 6.414; 95% CI, 2.1–19.3, P < 0.001) and high WT1 post-maintenance 3 month (HR = 7.533; 95% CI, 2.3–24.8, P < 0.001), and 4-year DFS was significantly inferior in patients with high peak leukocyte count (HR = 5.275; 95% CI, 1.9–14.7, P = 0.001) and high WT1 post-maintenance 3 month (HR = 8.241; 95% CI, 2.3–29.1, P = 0.001).

Unfortunately, our chemotherapy regimen was not differently specified for high-risk APL and the standard treatment of APL is now changed to a combination therapy using ATO. Therefore, current results may not be applicable in the treatment course using ATO and another validation is needed. Conclusively, high post-remission WT1 expression is a reliable marker for prediction of subsequent relapse in APL patients treated with conventional chemotherapy. For patients with high-risk of relapse, early intervention using WT1-specific therapy may prevent relapse and improve survival outcomes [8, 9].