Abstract
Background
AML with FLT3 ITD mutations are associated with poor outcome. We reviewed outcomes of patients with FLT3 ITD mutated AML to investigate trends over time.
Methods
We analyzed 224 AML patients (excluding patients with core binding factor and acute promyelocytic leukemia) referred to our institution between 2000 and 2014. Patients were divided into 5 cohorts by era: 2000–02 (Era 1, n=19), 2003–05 (Era 2, n=41), 2006–08 (Era 3, n=53), 2009–11 (Era 4, n=55), and 2012–14 (Era 5, n=56) to analyze differences in outcome.
Results
The baseline characteristics were not statistically different across Eras. The response rate (CR/CRp) from Era 1–5 was 68%, 49%, 72%, 73%, and 75% respectively. The overall response rate (all Eras) with chemotherapy alone versus chemotherapy plus FLT3 inhibitor was 67% and 72.5%, respectively (p= 0.4). The median time to relapse was 6, 3.6, 7.9, 8.1 months and not reached from Eras 1 through 5, respectively (p= 0.001). The median OS has improved: 9.6, 7.6, 14.4, 15.7 and 17.8 month from Eras 1–5, respectively (p= <0.001). Stem cell transplant as a time dependent variable, showed better OS in the univariate analysis (HR: 0.57, 95% CI: 0.39–0.84, p= 0.004) but did not retained its significance in multivariate analysis (HR: 0.75, 95% CI: 0.50–1.13, p= 0.16).
Conclusion
Our data suggest improvement in outcome of FLT3 ITD mutated AML patients over the last 15 years. This is probably due to improvement in treatment strategies, including but not limited to integration of FLT3 inhibitors and increased use of SCT.
Keywords: AML, FLT3 ITD mutations, FLT3 inhibitors, SCT
Introduction
FMS-like tyrosine kinase 3 (FLT3) plays vital role in hematopoiesis and leukemogenesis and when mutated, is an important adverse prognostic marker in acute myeloid leukemia (AML).[1–3] The two most common types of FLT3 mutations are internal tandem duplications (ITD) in the juxtamembrane domain, and point mutation in the activation loop of the tyrosine kinase domain (TKD), most commonly affecting aspartate (D835).[1–3] The FLT3 ITD occurs at a frequency of 20–30% in AML patients with diploid cytogenetics [4, 5] and is more frequently seen in younger (16–60 years) patients.[4, 6, 7] The FLT3 ITD leads to constitutive activation of receptor tyrosine kinase and downstream signaling through RAS/RAF/MEK/ERK kinases, STAT5 and PI3-kinases. This leads to increased leukemic stem and progenitor cell proliferation and survival.[8, 9] Clinically this translates into leucocytosis, higher percentage of blast, higher relapse rate and poor overall survival (OS) compared to patients with wild type (wt) FLT3.[5, 10–12] Although, the rate of complete remission in FLT3 ITD mutated AML are similar to other AML but responses are usually short lived with poorer responses to salvage therapies.[11] Conversely, the prognostic impact of TKD is more controversial with studies reporting both favorable and unfavorable outcomes.[13–15] Several series have reported the impact of FLT3 ITD allelic burden on clinical outcome. Interestingly, patients with high FLT3 ITD allelic burden appear to have a better response to FLT3 inhibition compared to those with low allelic burden.[16, 17]
The overwhelming evidence of poor prognosis associated with FLT3 ITD mutations has drawn considerable attention for development of new treatment strategies to improve outcome. The role of allogeneic stem cell transplant (SCT) as a consolidation strategy has been evaluated in several series.[18–20] SCT has demonstrated benefit in reducing the risk of relapse and improvement in survival. FLT3 inhibitors are also being evaluated in clinical trials in an attempt to improve outcome. Several studies have reported clinical activity of Lestaurtinib (CEP-701), Midostaurin (PKC412), Crenolanib (CP-868596), Quizartinib (AC220), and Sorafenib in patients with FLT3 ITD mutated AML treated either after failure of other treatment strategies or as initial therapy, when used either alone or in combination with other agents.[21–27]
Incorporating FLT3 inhibitor with chemotherapy and SCT in first complete remission (CR1) have the potential to improve outcome in poor prognostic, FLT3 ITD mutated AML. In this context we reviewed our data from 2000 to 2014 to evaluate difference in clinical outcome over the years with evolution of treatment strategies over time.
Patients and method
We retrospectively analyzed 1441 patients with AML evaluated at our institution between 2000 and 2014. FLT3 ITD was identified in 334 patients. After excluding patients with core binding factor leukemia and acute promyelocytic leukemia, 224 patients were included in this analysis. Among these 224 patients, 21 (9%) also had TKD (D835) mutation. Patients were divided into 5 cohorts by year of referral (henceforth referred to as “Era”: 2000–02 (Era 1, n=19), 2003–05 (Era 2, n=41), 2006–08 (Era 3, n=53), 2009–11 (Era 4, n=55), and 2012–14 (Era 5, n=56). Patient records were reviewed for baseline characteristics, treatment given, response to therapy, remission duration and overall survival. Cytogenetic risk was classified according to United Kingdom Medical Research Council (MRC) AML 10 trial.[28] Response to therapy was classified according to the International Working Group (IWG) criteria 2003.[29] Overall response rate (ORR) was defined as the sum of complete remission (CR), CR with incomplete platelet recovery (CRp), complete remission with incomplete count recovery (CRi), and partial remission (PR). Patients were included in a retrospective chart review approved by the Institutional Review Board.
Polymerase chain reaction assay for FLT3 mutations
FLT3 mutation analysis was performed as described previously by Lin et al.[30] Briefly, after the initial round of endpoint PCR using fluorescently labeled primers, PCR products for wild-type and mutant FLT3 were detected using capillary gel electrophoresis-based sizing. This assay evaluates both the internal tandem duplication (ITD) and the tyrosine kinase domain codon 835. The sensitivity of the assay is 1%. In addition to running appropriate positive, negative and sensitivity controls, each of the finding is confirmed by duplicate analysis. All reported results are thus based on reproducible results in duplicate analysis. ITD ratio is calculated as (mutant allele)/(mutant allele + wild type allele).
Statistical methods
Pearson chi-square (or Fisher’s exact test) and ANOVA (or Kruskal-Wallis’s rank sum) were used to determine difference in the demographics/clinical characteristics among the eras. A Trend test across groups was used to test if there was a trend in the proportion of patients achieving CR/CRp across eras. Univariate and multivariate Logistic regression models were used to model the relationship between response (No CR/CRp vs CR/CRp) and demographics/clinical characteristics.
Overall survival (OS) was calculated as the number of months from the date of diagnosis to death or last follow-up date. Patients who were alive at their last follow-up were censored on that date. Relapse-free survival (RFS) was calculated as the number of months from the date of response to the date of relapse or death. Patients who did not relapse at their last follow-up were censored on that date. The Kaplan-Meier product limit method was used to estimate the median OS. Univariate Cox proportional hazards regression was used to identify any association with each of the variables and OS (or RFS). In this analysis, SCT was treated as a time-dependent variable. Statistical analysis was performed using STATA/SE version 13.1 statistical software.
Results
Baseline characteristics are summarized in Table I. The median age at diagnosis for patients on each of the 5 eras was 57, 62, 59, 61, and 66 years, respectively (p= 0.55). There was a trend for a lower median white blood cell and platelet count in the more recent eras. The percentage of patients with diploid cytogenetics remained constant through the 5 treatment Eras, but there was a trend for an increase in the percentage of patients with poor risk cytogenetics[28] (6%, 0%, 12%, 6%, and 14%, from Era 1–5 respectively (p= 0.26). The median FLT3 ITD ratio from Era 1–5 was 0.1, 0.5, 0.3, 0.2 and 0.3 respectively (p= 0.59). Among 151 (67%) evaluable patients for NPM-1 mutation overall, 71 (47%) were positive for NPM-1 mutation; 33%, 61%, 36%, 50% and 48% from Era1 to 5 respectively (p = 0.56).
Table I.
Baseline characteristics
| Median [range], n (%)
|
|||||||
|---|---|---|---|---|---|---|---|
| Characteristics | Era 1 (n= 19) | Era 2 (n= 41) | Era 3 (n= 53) | Era 4 (n= 55) | Era 5 (n= 56) | Overall (n= 224) | p |
| Age in years | 57 [20–82] | 62 [17–85] | 59 [20–84] | 61 [23–89] | 66 [24–82] | 61 [17–89] | 0.55 |
| WBC x 109/L | 11.9 [3.8–74.8] | 17.3 [1–161.5] | 14.9 [1.4–129.5] | 9.4 [0.5–228.5] | 8 [0.5–191] | 11.3 [0.5–228.5] | 0.02 |
| WBC < 25 x 109/L | 13 (68) | 23 (56) | 36 (68) | 43 (78) | 45 (80) | 160 (71) | 0.07 |
| WBC > 25 x 109/L | 6 (32) | 18 (44) | 17 (32) | 12 (22) | 11 (20) | 64 (29) | |
| Hb (g/dl) | 7.7 [4.4–10.1] | 8 [4.9–11.7] | 8 [4.9–11.7] | 8.5 [5–11.7] | 9.2 [6.2–13.1] | 8.9 [4.4–13.1] | <0.001 |
| Platelet x 109/L | 60 [6–286] | 51 [7–295] | 55 [7–258] | 33 [6–270] | 35.5 [3–326] | 42.5 [3–326] | 0.003 |
| BM blast % | 64 [11–96] | 70 [20–96] | 73 [19–98] | 70 (16–95) | 68 [21–95] | 70 [11–98] | 0.59 |
| PB % | 39 [8–99] | 42 [0–97] | 46 [0–95] | 46 [0–98] | 46 [0–98] | 37.5 [0–99] | 0.59 |
| FLT3 ITD ratioa | 0.1 [0.01–0.8] | 0.5 [0.02–2.3] | 0.3 [0.01–1.3] | 0.2 [0.01–0.7] | 0.2 [0.01–0.6] | 0.3 [0.01–2.3] | 0.01 |
| Cytogenetics (28) | |||||||
| Diploid | 13 (72) | 35 (87.5) | 38 (76) | 38 (74) | 37 (72.5) | 161 (77) | 0.26 |
| Poor risk | 1 (6) | 0 (0) | 6 (12) | 3 (6) | 7 (14) | 17 (8) | |
| Miscellaneous | 4 (22) | 5 (12.5) | 6 (12) | 10 (20) | 7 (14) | 32 (15) | |
| NPM-1 mutationab | 2 (33) | 14 (61) | 8 (36) | 25 (50) | 24 (48) | 71 (47) | 0.56 |
| Induction Chemotherapy | |||||||
| Idarubicin + HDA based | 13 (68.4) | 16 (39) | 32 (60.4) | 21 (38.2) | 7 (12.5) | 89 (39.7) | <0.001 |
| HMA based | 0 (0) | 1 (2.4) | 13 (24.5) | 11 (20) | 25 (44.6) | 50 (22.3) | |
| NA + HDA based | 3 (15.8) | 7 (17.1) | 0 (0) | 2 (3.6) | 0 (0) | 12 (5.4) | |
| CIA or FIA | 0 (0) | 0 (0) | 0 (0) | 10 (18.2) | 17 (30.4) | 27 (12.1) | |
| NA +/− Investigational | 3 (15.8) | 17 (41.5) | 8 (15.1) | 11 (20) | 7 (12.5) | 46 (20.5) | |
| Chemotherapy with FLT3 inhibitor | |||||||
| Yes | 0 (0) | 1 (2) | 11 (21) | 11 (20) | 28 (50) | 51 (23) | |
| No | 19 (100) | 40 (98) | 42 (79) | 44 (80) | 28 (50) | 173 (77) | |
| FLT3 inhibitor never | 16 (84) | 36 (88) | 35 (66) | 27 (49) | 28 (50) | 142 (63) | <0.0001 |
| FLT3 inhibitor once** | 2 (10.5) | 5 (12) | 14 (26) | 21 (38) | 23 (41) | 65 (29) | |
| FLT3 inhibitor twice | 1 (5) | 0 (0) | 4 (7.5) | 7 (13) | 5 (9) | 17 (8) | |
| Type of FLT3 inhibitors used | <0.001 | ||||||
| Sorafenib | 0 (0) | 2 (33.3) | 12 (66.7) | 15 (53.6) | 10 (45.5) | 39 (50.6) | |
| Quizartinib | 2 (66.7) | 0 (0) | 4 (22.2) | 8 (28.6) | 2 (9.1) | 16 (20.8) | |
| Midostaurin | 0 (0) | 1 (16.7) | 0 (0) | 5 (17.9) | 6 (27.3) | 12 (15.6) | |
| Crenolinib | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 4 (18.2) | 4 (5.2) | |
| Lestaurtinib | 1 (33.3) | 3 (50) | 2 (11.1) | 0 (0) | 0 (0) | 6 (7.8) | |
WBC= white blood cell, Hb= hemoglobin, BM= bone marrow, PB= peripheral blood,
FLT3 ITD ratio available in 220 patients (17,39,53,55 and 56 from Era1–5 respectively), HMA= hypomethylating agents, NA= nucleoside analogues, HDA= high dose cytarabine, Invest.= investigational, CIA= clofarabine, Idarubicin and Ara C, FIA= fludarabine, Idarubicin and Ara C.
FLT3 inhibitor at any time during treatment course. ® Two different FLT3 inhibitor at different time interval alone or in combination with chemotherapy during treatment course.
73 patients overall (13; Era 1, were not evaluated for NPM-1 mutation.
Induction chemotherapy
As shown in Table 1, patients received different induction chemotherapy regimens based on available clinical trials, their age and performance status. For the purpose of analysis induction chemotherapy regimens were grouped as follows: idarubicin plus high-dose Ara C-based (HDAC ≥1000mg/m2/day), hypomethylating agent (HMA; azacytidine or decitabine) based, nucleoside analogues (clofarabine or fludarabine) plus HDAC, CIA (clofarabine, Idarubicin and HDAC) or FIA (fludarabine, idarubicin and HDAC), and nucleoside analogues plus investigational agents. (Patients received these chemotherapy regimens with or without FLT3 inhibitors). There are imbalances in the percentage of patients treated on these regimens, over different Eras.
FLT3 inhibitors
Overall, 65 patients (29%; n=2, 5, 14, 21, and 23, respectively in Eras 1 through 5) received a FLT3 inhibitor alone or in combination with chemotherapy at least once during the course of their treatment. Among them 17 patients (8%; n=1, 0, 4, 7 and 5 respectively in Era 1 through 5) received FLT3 inhibitors twice, either alone or in combination with chemotherapy. In contrast, 142 (63%; n=16, 36, 35, 27 and 28, in Era 1 through 5 respectively) patients never received a FLT3 inhibitor. As expected, higher percentage of patients never received a FLT3 inhibitor during their disease course.
Different FLT3 inhibitors were used under various clinical trials, alone or in combination with chemotherapy. The most commonly used FLT3 inhibitor was sorafenib in 39 patients (50.6% of all patients treated with FLT3 inhibitors). Other patients received quizartinib, midostaurin, lestaurtinib, and crenolinib alone or in combination with chemotherapy (Table I).
Stem cell transplant
Overall 77 (34%) received a stem cell transplant (SCT) during the course of their management. The proportion of patient receiving SCT increased over time from 5 patients in the first Era, to 6, 21, 27, and 18 in subsequent Eras, respectively (p= 0.03). Overall majority of patients received SCT in first complete remission 47 (21%; n= 4, 1, 10, 18 and 14, respectively in Eras 1 through 5, p= 0.002) (Supplemental table I).
Response
The rate of complete remission (CR)/complete remission with incomplete platelet recovery (CRp) from Eras 1 through 5 were 68%, 49%, 72%, 73%, and 75%, respectively (Table II). In a subset analysis, we analyzed the response combining all patients who received chemotherapy alone (n=173) compared to those who received chemotherapy plus a FLT3 inhibitor during induction (n= 51). The rate of CR/CRp was 67% in the chemotherapy group and 72.5% in the chemotherapy plus FLT3 inhibitor group (p= 0.45) (Supplemental Table II).
Table II.
Response to induction chemotherapy by Era; N (%)
| Responses to induction chemotherapy | Overall | Era 1 | Era 2 | Era 3 | Era 4 | Era 5 | p-value* |
|---|---|---|---|---|---|---|---|
| No CR/CRp | 71 (32) | 6 (32) | 21 (51) | 15(28) | 15(27) | 14(25) | 0.057 |
| CR/CRp | 153 (68) | 13 (68) | 20 (49) | 38 (72) | 40 (73) | 42 (75) | |
| p-value** | |||||||
| ORR | 0.003 | ||||||
| CR | 136 (61) | 12 (63) | 19 (46) | 37 (70) | 36 (65.5) | 32(57) | |
| CRp | 17 (8) | 1 (5) | 1 (2) | 1 (2) | 4 (7) | 10 (18) | |
| CRi | 8 (4) | 0 (0) | 1 (2) | 0 (0) | 3 (5.5) | 4 (7) | |
| PR | 5 (2) | 1 (5) | 0 (0) | 1 (2) | 3 (5.5) | 0 (0) | |
| Others | |||||||
| NR | 51 (23) | 5 (26) | 15 (36) | 13 (24.5) | 8 (14.5) | 10 (18) | |
| Died | 7 (3) | 0 (0) | 5 (12) | 1 (2) | 1 (2) | 0 (0) | |
Trend test across ordered groups
Pearson’s chi-squared test
Treatment related mortality (≤4 weeks from induction chemotherapy)
Five (12%) patients in Era 2, and one patient each in Eras 4 and 5 died in the first 4 weeks from start of induction (i.e., treatment related mortality (TRM); no patients in Eras 1 and 3 had TRM. Among the 7 patients who died early, 4 died of sepsis, 2 from diffuse alveolar hemorrhage and 1 from intracerebral hemorrhage.
Outcome
The median time (in months) to relapse was 6, 3.6, 7.9, 8.1 and not reached (NR) in Eras 1 through 5, respectively, (p= 0.001; Fig. 1). The median overall survival (OS) improved over time from Era 1 to 5: 9.6, 7.6, 14.4, 15.7 and 17.8 months, respectively (p= <0.001; Fig. 2). In a subset analysis, excluding patients who had SCT in CR1, the median overall survival in Eras 1 through 5 was 9.2, 7.5, 12.8, 13.2 and 9.2 months, respectively (p= 0.04). Among patients who achieved CR/CRp, the median OS was 13.6, 10.4, 16, 20 and 17.8 months, respectively (p= 0.05)
Fig. 1.
Fig. 2.
Univariate analysis
Logistic regression models were used to identify factors associated with CR/CRp. Among the variables evaluated, age more than 60 years was significantly associated with inferior CR/CRp rate (odds ratio [OR]: 0.31, 95% CI: 0.17–0.57, p 0.001). The rate of CR/CRp to CIA/FIA based induction chemotherapy was significantly associated with better response rate compared to HMA (OR: 0.11, 95% CI; 0.03–0.40, p 0.001) but not with IA-based induction chemotherapy (OR: 0.57, 95% CI: 0.15–2.13, p 0.40). White blood cell (WBC) >25 x 109 /L, poor risk cytogenetics (CG) and FLT3 ITD mutation burden > 0.78 were not associated with difference in response to chemotherapy (supplemental Table IIIa).
We then performed a univariate analysis to identify factors associated with an increased probability of relapse in patients who achieved CR/CRp. Age more than 60 years and baseline WBC >25 x 109/L was associated with a statistically significant higher probability of relapse (hazard ratio [HR]:1.36, 95% CI: 1.00–1.87, p= 0.052 and HR: 1.56, 95% CI: 1.12–2.17 and p= 0.009), respectively. Similarly, use of hypomethylating agent (HMA)-based induction chemotherapy was associated with a high likelihood of early relapse compared to CIA/FIA based induction chemotherapy regimens (HR; 1.76, 95%CI: 0.94–3.30, p= 0.077). In contrast, SCT at any time and FLT3 ITD ratio ≥0.78 did not appear to have a significant impact on the probability of relapse (Supplement table IV).
In a univariate analysis for OS; age ≥60 years, and WBC >25 x 109/L were associated with a significantly inferior probability of survival (HR: 1.64, 95% CI: 1.19–2.28, p= 0.003) and (HR: 1.70, 95% CI: 1.21–2.39, p= 0.002) respectively. In contrast, stem cell transplant at any time as a time dependent variable was associated with better OS compared to those patients without SCT (18.4 vs 10.6 months; HR: 0.57, 95% CI: 0.39–0.84 and p = 0.004). Similarly, CIA/FIA based induction chemotherapy was associated with better OS (17.7 months) compared to IA (15.5), HMA (10.2 months) and others investigational agents (8.3 months) containing chemotherapy regimens (p=0.001) (Supplemental table V).
Multivariate analysis
When we performed multivariate analysis for response (CR/CRp) rate using logistic regression model, HMA based induction chemotherapy was inferior to CIA/FIA based induction chemotherapy (OR: 0.10, 95% CI: 0.02–0.47, p= 0.004). Whereas, IA based induction chemotherapy was also inferior to CIA/FIA based induction chemotherapy but not statistically significant (OR: 0.57, 95% CI: 0.15–2.12, p= 0.39). Age did not retained prognostic significance for CR/CRp in multivariate analysis (supplemental table IIIb).
In multivariate analysis for RFS, WBC >25 x 109/L retained poor prognostic significance (HR: 1.63, 95% C: 1.16–2.29, p= 0.005). Age, SCT at any time as time dependent variable, CIA/FIA based induction chemotherapy compared to IA or HMA based or others therapy did not show prognostic significance (supplemental table VI).
In multivariate analysis for OS, WBC >25 x 109/L retained poor prognostic significance (HR: 1.63, 95% CI: 1.14–2.33, p= 0.007). SCT at any time as time dependent variable failed to retained prognostic significance in multivariate analysis (HR: 0.75, 95% CI: 0.50–1.13, p= 0.166). CIA/FIA based induction chemotherapy didn’t retained favorable prognostic significance for OS when compared to HMA based induction (HR: 1.84, 95% CI: 0.80–4.24, p= 0.150 or IA or other therapies (supplemental Table VII).
Discussion
In this report, we present an analysis of the outcome of a large number of patients with FLT3 ITD mutated AML treated over the last one and a half decades. Our results show a significant improvement in the outcome of patients with FLT3 ITD mutated AML over the years. Moreover, a higher proportion of patients received FLT3 inhibitors and had a SCT.
Outcome of FLT3 ITD mutated AML remains challenging. As we have learned more about the disease dynamics, treatment strategies have changed and continued to evolve. One major change in the treatment of this population with high-risk AML is the development of FLT3 inhibitors. Several FLT3 inhibitors have been evaluated in clinical trials for safety and efficacy, although all remain investigational at the time of this writing. While FLT3 inhibitors have demonstrated they can induce rapid clearance of peripheral leukemic blast and a reduction of bone marrow blasts in up to 50–60% of patients, these responses tend to be associated with incomplete recovery of normal hematopoiesis (i.e., CRi more frequently than CR) and transient when these agents are used by themselves. There are several reasons for the incomplete and transient nature of the responses. It has been reported that the bone marrow microenvironment can support survival of the neoplastic cells through persistent activation of survival signaling pathways such as AKT, ERK and STAT-3.[31] In addition, secondary mutations can develop, that may be more resistant to many of the available FLT3 inhibitors.[32] In an analysis of patients with AML FLT3 ITD, treated with FLT3 inhibitors in several studies, 22% developed D835 at the time of emergence of resistance.[33] Notably, sorafenib, quizartinib and other FLT3 inhibitors have shown minimal to no inhibitory activity against this mutation in preclinical models. New FLT3 inhibitors with in vitro activity against resistance mutations, such as crenolanib [21], ASP2215 and FLX925 (previously known AMG925) are currently being explored in the clinic.[34, 35]
In an effort to try to overcome this resistance, combined treatment approaches of FLT3 inhibitors with conventional chemotherapy or hypomethylating agents are being developed. In vitro, studies have reported FLT3 inhibitors acts synergistically with chemotherapy to induce cytotoxicity.[36, 37] A phase I/II study of sorafenib in combination with idarubicin and cytarabine showed improved responses in younger patients with FLT3 ITD mutated AML and similar toxicity profile to chemotherapy alone.[23] In a recent study younger AML patients were randomized to receive either sorafenib or placebo combined with standard anthracycline plus cytarabine.[38] With median follow up of 3 years, the RFS was 38% and 56% with placebo and sorafenib arms respectively (p= 0.01). Improved OS was observed in the sorafenib arm (63% vs 56%, respectively on 3 years follow up) (p= 0.38). Among 46 (17%) patients with FLT3 ITD mutated, trend for better RFS and OS in favor of sorafenib was observed. A combination of azacytidine with sorafenib has also shown to produce a response rate of 46% (CR 27%, CRi 16%, and PR 3%) in patients with relapsed or refractory FLT3 ITD mutated AML.[39]
In our analysis higher number of patients achieved CR/CRp in successive Eras. Importantly, the rate of response in Era 2 is particularly low. If these results are excluded from the trend analysis, there is no significant difference in outcome over time (trend analysis p value 0.55). In subset analysis, comparing responses to induction chemotherapy alone vs chemotherapy plus FLT3 inhibitor, there was a slightly better CR/CRp rate of (67% vs 72.5%; p= 0.45) respectively. The number of patients offered these combinations as initial therapy is still relatively small. As the use of this combination strategy increases, this might translate into a more noticeable benefit.
In this report, the increased use of SCT in successive Eras is likely to have contributed to the improved outcome over time. Remissions in patients with FLT3 ITD are usually short-lived and once relapse, it usually presents with higher FLT3 ITD mutation burden and poorer response to treatment.[11] The SCT in CR1 has thus been advocated as the optimal strategy for consolidation therapy. Recent series have reported improve long term outcome in FLT3 ITD mutated AML if SCT is done in CR1.[20] Our historical review, showed increasing trend for SCT with passage of time and more so in CR1. Confirming earlier observations, SCT as a time dependent variable resulted in improved OS compared to no SCT in univariate analysis, but did not retained prognostic significance in multivariate analysis. Importantly however, there is still a high risk of relapse after SCT, and better strategies to maintain remissions after SCT are needed. Several studies are ongoing exploring the use of FLT3 inhibitors as maintenance therapy after SCT.
We believe our analysis is informative but also has limitations that must be acknowledged. First, there could be bias involved in patient selection. Since FLT3 inhibitors are largely experimental at the time, they are only available through clinical trials. Eligibility criteria for these trials by necessity select patients in an overall better health. In contrast, patients with more proliferative disease and/or with more co-morbidities and concomitant medications of the sort that are usually not allowed in clinical trials tend to be managed in emergency situations and outside of clinical trials. All patients included in this analysis were enrolled in clinical trials. The result and conclusion of this analysis may not fully apply to patients, who are not eligible for clinical trials. Secondly, the patient populations in our analysis are quiet heterogeneous. Patients have received different chemotherapy regimens in successive Eras and received different FLT3 inhibitors with distinct potencies and pharmacological properties. We evaluated FLT3 inhibitor as a single therapeutic entity but some of the more modern FLT3 inhibitors may be more specific and possibly more effective, particularly against tyrosine kinase mutations than sorafenib. There is also variability in the type of transplant, from the source of donor to the conditioning regimen and GVHD prophylaxis. These variables all may play a role in outcome and we cannot adjust for all of them in an analysis like the one we performed. The weakness of retrospective analysis can be overcome in future prospective studies. Finally, the definition of Eras by three-year periods is arbitrary. To determine whether the results are an artifice of the definition of Eras chosen for the analysis we also performed an analysis dividing the study period into only two Eras, 2000–2007 and 2008–2014. The RFS was 5.8 vs 8.6 months in these two Eras, respectively (p = 0.01). Similarly OS was 9.4 vs 16 months, respectively (p= 0.007). This suggests that the trends observed in the analysis might be real. Importantly, the outcome appears to be particularly inferior for patients treated during Era 2. No clear difference in patient characteristics can be identified in our analysis for this patient population, but these patients were among the highest proportion of patient treated with a nucleoside analog and an investigational agent compared to all other eras.
In conclusion, our data suggested improvement in outcome of FLT3 ITD mutated AML patients over the last decade and a half. This is probably due to more aggressive treatment strategies including earlier use of SCT. The use of FLT3 inhibitors may have also contributed, mostly by increasing probability of achieving remission thus making SCT a more viable option. Still, much research is needed to further improve the outcome for this subset of poor prognostic AML patients.
Supplementary Material
Acknowledgments
MD Anderson Cancer Center receives support Grant CA016672 and the MD Anderson Cancer Center Leukemia SPORE CA100632 from the National Cancer Institute.
The authors would like to thank for grant support from Arog, Ariad, Ambit, Astellas, Flexus, and Novartis.
Footnotes
Disclosures: All authors declare that they have no conflict of interest.
References
- 1.Kottaridis PD, Gale RE, Linch DC. Flt3 mutations and leukaemia. British journal of haematology. 2003;122:523–538. doi: 10.1046/j.1365-2141.2003.04500.x. [DOI] [PubMed] [Google Scholar]
- 2.Naoe T, Kiyoi H. Normal and oncogenic FLT3. Cellular and molecular life sciences : CMLS. 2004;61:2932–2938. doi: 10.1007/s00018-004-4274-x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Thiede C, Steudel C, Mohr B, et al. Analysis of FLT3-activating mutations in 979 patients with acute myelogenous leukemia: association with FAB subtypes and identification of subgroups with poor prognosis. Blood. 2002;99:4326–4335. doi: 10.1182/blood.v99.12.4326. [DOI] [PubMed] [Google Scholar]
- 4.Frohling S, Schlenk RF, Breitruck J, et al. Prognostic significance of activating FLT3 mutations in younger adults (16 to 60 years) with acute myeloid leukemia and normal cytogenetics: a study of the AML Study Group Ulm. Blood. 2002;100:4372–4380. doi: 10.1182/blood-2002-05-1440. [DOI] [PubMed] [Google Scholar]
- 5.Kiyoi H, Naoe T, Nakano Y, et al. Prognostic implication of FLT3 and N-RAS gene mutations in acute myeloid leukemia. Blood. 1999;93:3074–3080. [PubMed] [Google Scholar]
- 6.Lazenby M, Gilkes AF, Marrin C, et al. The prognostic relevance of flt3 and npm1 mutations on older patients treated intensively or non-intensively: a study of 1312 patients in the UK NCRI AML16 trial. Leukemia. 2014;28:1953–1959. doi: 10.1038/leu.2014.90. [DOI] [PubMed] [Google Scholar]
- 7.Schneider F, Hoster E, Schneider S, et al. Age-dependent frequencies of NPM1 mutations and FLT3-ITD in patients with normal karyotype AML (NK-AML) Annals of hematology. 2012;91:9–18. doi: 10.1007/s00277-011-1280-6. [DOI] [PubMed] [Google Scholar]
- 8.Fenski R, Flesch K, Serve S, et al. Constitutive activation of FLT3 in acute myeloid leukaemia and its consequences for growth of 32D cells. British journal of haematology. 2000;108:322–330. doi: 10.1046/j.1365-2141.2000.01831.x. [DOI] [PubMed] [Google Scholar]
- 9.Hayakawa F, Towatari M, Kiyoi H, et al. Tandem-duplicated Flt3 constitutively activates STAT5 and MAP kinase and introduces autonomous cell growth in IL-3-dependent cell lines. Oncogene. 2000;19:624–631. doi: 10.1038/sj.onc.1203354. [DOI] [PubMed] [Google Scholar]
- 10.Wagner K, Damm F, Thol F, et al. FLT3-internal tandem duplication and age are the major prognostic factors in patients with relapsed acute myeloid leukemia with normal karyotype. Haematologica. 2011;96:681–686. doi: 10.3324/haematol.2010.034074. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Ravandi F, Kantarjian H, Faderl S, et al. Outcome of patients with FLT3-mutated acute myeloid leukemia in first relapse. Leukemia research. 2010;34:752–756. doi: 10.1016/j.leukres.2009.10.001. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Kottaridis PD, Gale RE, Frew ME, et al. The presence of a FLT3 internal tandem duplication in patients with acute myeloid leukemia (AML) adds important prognostic information to cytogenetic risk group and response to the first cycle of chemotherapy: analysis of 854 patients from the United Kingdom Medical Research Council AML 10 and 12 trials. Blood. 2001;98:1752–1759. doi: 10.1182/blood.v98.6.1752. [DOI] [PubMed] [Google Scholar]
- 13.Yamamoto Y, Kiyoi H, Nakano Y, et al. Activating mutation of D835 within the activation loop of FLT3 in human hematologic malignancies. Blood. 2001;97:2434–2439. doi: 10.1182/blood.v97.8.2434. [DOI] [PubMed] [Google Scholar]
- 14.Mead AJ, Gale RE, Hills RK, et al. Conflicting data on the prognostic significance of FLT3/TKD mutations in acute myeloid leukemia might be related to the incidence of biallelic disease. Blood. 2008;112:444–445. doi: 10.1182/blood-2008-04-150003. author reply 445. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Whitman SP, Ruppert AS, Radmacher MD, et al. FLT3 D835/I836 mutations are associated with poor disease-free survival and a distinct gene-expression signature among younger adults with de novo cytogenetically normal acute myeloid leukemia lacking FLT3 internal tandem duplications. Blood. 2008;111:1552–1559. doi: 10.1182/blood-2007-08-107946. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Pratcorona M, Brunet S, Nomdedeu J, et al. Favorable outcome of patients with acute myeloid leukemia harboring a low-allelic burden FLT3-ITD mutation and concomitant NPM1 mutation: relevance to post-remission therapy. Blood. 2013;121:2734–2738. doi: 10.1182/blood-2012-06-431122. [DOI] [PubMed] [Google Scholar]
- 17.Pratz KW, Sato T, Murphy KM, et al. FLT3-mutant allelic burden and clinical status are predictive of response to FLT3 inhibitors in AML. Blood. 2010;115:1425–1432. doi: 10.1182/blood-2009-09-242859. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Bornhauser M, Illmer T, Schaich M, et al. Improved outcome after stem-cell transplantation in FLT3/ITD-positive AML. Blood. 2007;109:2264–2265. doi: 10.1182/blood-2006-09-047225. author reply 2265. [DOI] [PubMed] [Google Scholar]
- 19.Brunet S, Labopin M, Esteve J, et al. Impact of FLT3 internal tandem duplication on the outcome of related and unrelated hematopoietic transplantation for adult acute myeloid leukemia in first remission: a retrospective analysis. Journal of clinical oncology : official journal of the American Society of Clinical Oncology. 2012;30:735–741. doi: 10.1200/JCO.2011.36.9868. [DOI] [PubMed] [Google Scholar]
- 20.DeZern AE, Sung A, Kim S, et al. Role of Allogeneic Transplantation for FLT3/ITD Acute Myeloid Leukemia: Outcomes from 133 Consecutive Newly Diagnosed Patients from a Single Institution. Biology of Blood and Marrow Transplant. 17:1404–1409. doi: 10.1016/j.bbmt.2011.02.003. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Galanis A, Ma H, Rajkhowa T, et al. Crenolanib is a potent inhibitor of FLT3 with activity against resistance-conferring point mutants. Blood. 2014;123:94–100. doi: 10.1182/blood-2013-10-529313. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Man CH, Fung TK, Ho C, et al. Sorafenib treatment of FLT3-ITD(+) acute myeloid leukemia: favorable initial outcome and mechanisms of subsequent nonresponsiveness associated with the emergence of a D835 mutation. Blood. 2012;119:5133–5143. doi: 10.1182/blood-2011-06-363960. [DOI] [PubMed] [Google Scholar]
- 23.Ravandi F, Cortes JE, Jones D, et al. Phase I/II study of combination therapy with sorafenib, idarubicin, and cytarabine in younger patients with acute myeloid leukemia. Journal of clinical oncology : official journal of the American Society of Clinical Oncology. 2010;28:1856–1862. doi: 10.1200/JCO.2009.25.4888. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Smith BD, Levis M, Beran M, et al. Single-agent CEP-701, a novel FLT3 inhibitor, shows biologic and clinical activity in patients with relapsed or refractory acute myeloid leukemia. Blood. 2004;103:3669–3676. doi: 10.1182/blood-2003-11-3775. [DOI] [PubMed] [Google Scholar]
- 25.Stone RM, De Angelo J, Galinsky I, et al. PKC 412 FLT3 inhibitor therapy in AML: results of a phase II trial. Annals of hematology. 2004;83(Suppl 1):S89–90. doi: 10.1007/s00277-004-0850-2. [DOI] [PubMed] [Google Scholar]
- 26.Zarrinkar PP, Gunawardane RN, Cramer MD, et al. AC220 is a uniquely potent and selective inhibitor of FLT3 for the treatment of acute myeloid leukemia (AML) Blood. 2009;114:2984–2992. doi: 10.1182/blood-2009-05-222034. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Cortes JE, Kantarjian H, Foran JM, et al. Phase I study of quizartinib administered daily to patients with relapsed or refractory acute myeloid leukemia irrespective of FMS-like tyrosine kinase 3-internal tandem duplication status. Journal of clinical oncology : official journal of the American Society of Clinical Oncology. 2013;31:3681–3687. doi: 10.1200/JCO.2013.48.8783. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Grimwade D, Walker H, Oliver F, et al. The importance of diagnostic cytogenetics on outcome in AML: analysis of 1,612 patients entered into the MRC AML 10 trial. The Medical Research Council Adult and Children’s Leukaemia Working Parties Blood. 1998;92:2322–2333. [PubMed] [Google Scholar]
- 29.Cheson BD, Bennett JM, Kopecky KJ, et al. Revised recommendations of the International Working Group for Diagnosis, Standardization of Response Criteria, Treatment Outcomes, and Reporting Standards for Therapeutic Trials in Acute Myeloid Leukemia. Journal of clinical oncology : official journal of the American Society of Clinical Oncology. 2003;21:4642–4649. doi: 10.1200/JCO.2003.04.036. [DOI] [PubMed] [Google Scholar]
- 30.Lin P, Jones D, Medeiros LJ, et al. Activating FLT3 mutations are detectable in chronic and blast phase of chronic myeloproliferative disorders other than chronic myeloid leukemia. American journal of clinical pathology. 2006;126:530–533. doi: 10.1309/JT5BE2L1FGG8P8Y6. [DOI] [PubMed] [Google Scholar]
- 31.Tabe Y, Jin L, Tsutsumi-Ishii Y, et al. Activation of integrin-linked kinase is a critical prosurvival pathway induced in leukemic cells by bone marrow-derived stromal cells. Cancer research. 2007;67:684–694. doi: 10.1158/0008-5472.CAN-06-3166. [DOI] [PubMed] [Google Scholar]
- 32.Smith CC, Wang Q, Chin CS, et al. Validation of ITD mutations in FLT3 as a therapeutic target in human acute myeloid leukaemia. Nature. 2012;485:260–263. doi: 10.1038/nature11016. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 33.Alvarado Y, Kantarjian HM, Luthra R, et al. Treatment with FLT3 inhibitor in patients with FLT3-mutated acute myeloid leukemia is associated with development of secondary FLT3-tyrosine kinase domain mutations. Cancer. 2014;120:2142–2149. doi: 10.1002/cncr.28705. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 34.Li C, Liu L, Liang L, et al. AMG 925 Is a Dual FLT3/CDK4 Inhibitor with the Potential to Overcome FLT3 Inhibitor Resistance in Acute Myeloid Leukemia. Molecular cancer therapeutics. 2015;14:375–383. doi: 10.1158/1535-7163.MCT-14-0388. [DOI] [PubMed] [Google Scholar]
- 35.Mori M, Kaneko N, Ueno Y, et al. ASP2215, a novel FLT3/AXL inhibitor: Preclinical evaluation in acute myeloid leukemia (AML) ASCO Meeting Abstracts. 2014;32:7070. [Google Scholar]
- 36.Yee KW, Schittenhelm M, O’Farrell AM, et al. Synergistic effect of SU11248 with cytarabine or daunorubicin on FLT3 ITD-positive leukemic cells. Blood. 2004;104:4202–4209. doi: 10.1182/blood-2003-10-3381. [DOI] [PubMed] [Google Scholar]
- 37.Levis M, Pham R, Smith BD, et al. In vitro studies of a FLT3 inhibitor combined with chemotherapy: sequence of administration is important to achieve synergistic cytotoxic effects. Blood. 2004;104:1145–1150. doi: 10.1182/blood-2004-01-0388. [DOI] [PubMed] [Google Scholar]
- 38.Röllig C, Müller-Tidow C, Hüttmann A, et al. Sorafenib Versus Placebo in Addition to Standard Therapy in Younger Patients with Newly Diagnosed Acute Myeloid Leukemia. Results from 267 Patients Treated in the Randomized Placebo-Controlled SAL-Soraml Trial. 2014:6–6. [Google Scholar]
- 39.Ravandi F, Alattar ML, Grunwald MR, et al. Phase 2 study of azacytidine plus sorafenib in patients with acute myeloid leukemia and FLT-3 internal tandem duplication mutation. Blood. 2013;121:4655–4662. doi: 10.1182/blood-2013-01-480228. [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.