Effective treatment with Gilteritinib-based regimens for FLT3-mutant extramedullary relapse in acute promyelocytic leukemia

ABSTRACT

Objective:

Extramedullary relapse (EMR) is rare in acute promyelocytic leukemia (APL) and, there is a lack of information on its management. Current practices for EMR in APL are always to adopt strategies from other subtypes of Acute lymphoblastic leukemia (ALL) and Acute myeloid leukemia (AML). Gilteritinib, a highly selective FLT3 inhibitor, has demonstrated a remarkable effect on EMR in FLT3-mutant AML. Therefore, it is worthwhile exploring if FLT3 mutation can be a therapeutic target and assessing the efficacy of Gilteritinib on FLT3-mutant EMR in APL.

Methods:

We described three cases of FLT3-mutant EMR in APL, comprising two isolated EMR cases and one systemic relapse. The patients underwent treatment with Gilteritinib-based regimens based on FLT3 mutation.

Results:

All three patients achieved complete regression of EMR, and no signs of tumor lysis syndrome during Gilteritinib-based therapy, only patient 1 showed mild granulocytopenia. They all maintained molecular complete remission (mCR) during the follow-up period.

Conclusions:

The Gilteritinib-based regimen shows a high and sustained therapeutic effect with minimal adverse effects, and provides a valuable experience for further evaluation in EMR APL patients.

KEYWORDS:

• Acute promyelocytic leukemia
• Extramedullary relapse
• FLT3 mutation
• Gilteritinib

Introduction

Acute promyelocytic leukemia (APL) is defined by the balanced translocation between chromosomes 15 and 17, resulting in the formation of PML-RARA [1]. Extraordinary advances have been achieved in treating APL by combining all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). However, in addition to this major translocation, patients with APL may have other molecular abnormalities that may interfere with the therapeutic efficacy of these specific drugs [2,3]. Among the recurrent somatic mutations, FLT3 mutation, including internal tandem duplication (ITD) and tyrosine kinase domain (TKD), is the most frequent co-occurring event to PML-RARA in APL and is associated with hyperleukocytosis and poor prognosis [4,5]. Previous research has confirmed that activating mutations of FLT3 have a noteworthy impact on APL pathogenesis and therapy response [6]. As EMR is rare, few studies report the landscape of mutations and even fewer on whether FLT3 mutation can be a therapeutic target.

The present study reports three cases of APL with EMR in a non-trial setting treated with Gilteritinib-based regimens at their physician’s discretion, which resulted in rapid and sustained remission.

Case presentation

Patient 1

An 18-year-old, previously healthy male, was admitted to the hospital due to rhinorrhagia in December 2009. His complete blood cell counts were as follows: White blood cell (WBC)8.25 × 10⁹/L, hemoglobin level (Hb) 11.2 g/dL, platelet count (PLT) 17 × 10⁹/L. The blasts were positive for myeloid markers, including cyMPO (59%), CD33 (99%), CD13 (25%), CD117 (87%), CD64 (56%), as well as the T lineage marker CD2 (50%) by flow cytometry. Cytogenetic analysis of the BM indicated t (15;17) (q24; q21). qRT-PCR detected PML/RARα S type transcripts (409 copies/10,000 nucleated cells). The patient was diagnosed with high-risk APL and treated with a combination of ATRA (25 mg/m²/day, twice daily, day 1∼28), ATO (0.16 mg/kg/day, day 1∼28), and daunorubicin (45 mg/m², 3 days) for induction therapy, and resulted in complete remission (CR). He suffered a cerebral hemorrhage during this period and had two subsequent bone marrow relapses in 2014 and 2018 (Figure 1), both achieved CR with ATRA combined with ATO. HLA-matched umbilical cord blood transplantation (UCBT) was performed on April 15, 2019, and granulocytes were engrafted on the 16th day. However, less than one year after UCBT, he had pain in the left external auditory meatus. Positron emission tomography-computed tomography (PET-CT) (Figure 2(A)) showed a hypermetabolic lesion in the left external auditory meatus (SUV value = 6.9). Histopathological examination revealed that MPO (+), CD33 (+), CD68 (+), CD117 (+), S100(+), CD34 (+), CD13 (+) and Ki-67 (70%+). Fluorescent in situ hybridization (FISH) revealed 70% of the tumor cells were positive for PML/RARα, while BM was found to be in mCR. Thus, the first isolated EMR after UCBT was diagnosed. He then received decitabine plus ATRA and ATO chemotherapy with local radiotherapy, which resulted in the disappearance of the EMR on June 4th, 2020 (Figure 2(B)). However, in February 2021, the patient complained of a right lumber mass and the pathology showed that it was the second EMR. He was then treated with decitabine plus Chidamide and Sintilima but had no response. In November 2021, the patient was hospitalized because he had an additional left lumber mass.BM still remained an mCR and complete chimerism of the donor cells. Histopathological examination of the lumber mass revealed MPO (+), CD43 (+), CD68 (+), CD117 (+), CD34 (+), CD13 (+), and Ki-67 (70%+). FISH indicated that 40% of tumor cells were positive for PML/RARα. FLT3-ITD was positive in EMR but undetectable in the BM. We treated the third EMR with Gilteritinib (120 mg, d1∼d28) combined with Venetoclax (100 mg d1, 200 mg d2, 400 mg d3∼28) and Azacitidine (75 mg/m², d1∼d7) for the first month, Gilteritinib (120 mg, d1∼d28) combined with ATRA (20 mg, twice a day, d1∼d14) and Realgar–indigo naturalis formula (5 tablets, three times a day, d15∼d28) for the second month, then followed by a 14 days rest. The 2.5-month therapy is a cycle (Table 1). After the first cycle of treatment, PET-CT showed that the hypermetabolic lesion disappeared (Figure 2(C)). The patient received an additional 4 cycles of treatments and is in mCR for 18 months.

Figure 1. Clinical time courses and treatment of the three patients.

Figure 2. (A) PET-CT images of the head and whole body of the patient 1. Red arrows indicate the EMR in the left external auditory meatusa. (B) PET-CT after decitabine plus ATRA and ATO combination chemotherapy with local radiotherapy, which resulted in disappearance of the EMR in the left external auditory meatusa. (C) PET-CT after 1 month of Gilteritinib therapy showing complete disappearance of the EMR in the left lumber.

Table 1. Clinical characteristics and therapeutic regimens of the three patients.

NO.	Age at relapse/sex	Leukemia status	Upfront treatment	Time from CR to first relapse	Localization of EMR	BM Status	Mutations	Gilteritinib-based regimens
1	30/M	The third EMD after UCBT	1.ATRA, ATO and DNR for induction and consolidation; 2. UCBT after second hematologic relapse; 3 ATRA, ATO, chemotherapy with local radiotherapy for first EMR;	4.8y	skin	mCR	BM: negative EMD: FLT3-ITD (AR = 0.85); CALR; ARIDIB; ARID2; BIRC3; EGFR	Gilteritinib (120 mg, d1∼d28) +Ven (100 mg d1, 200 mg d2, 400 mg d3∼28) + AZA (75 mg/m^2, d1∼d7) for the first month; Gilteritinib (120 mg, d1∼d28) + ATRA (25 mg/m^2/d, d1∼d14) and RIF (60 mg/kg/d, d15∼d28) for the second month, then followed by a 14days rest. 2.5 months therapy unit a cycle.
2	43/M	The second EMR	1.ATRA and ATO for induction and consolidation; 2. ATRA and ATO for first hematologic relapse and EMR	12y	CNS	mCR	BM: negative EMD: WT1, FLT3(D835Y)	ATO (0.16 mg/kg/d for 2 weeks every 4 months) or RIF (60 mg/kg/d for 2 weeks every 4 months) +ATRA (25 mg/m2/d for 4 weeks on 4 weeks off) + Gilteritinib (120 mg/d for 3 months on month off).4 months therapy unit a cycle.
3	73/M	Molecular relapse and the first EMR	1. ATRA combined chemotherapy for induction and consolidation; 2. ATRA and ATO for maintenance	1.7y	CNS	CR^MRD+	BM: FLT3-ITD (AR = 0.85) EMD: FLT3-ITD (47.07%)	ATO (0.16 mg/kg/d for 4 weeks on 4 weeks off) +ATRA (25 mg/m^2/d for 2 weeks on 2 weeks off) +Gilteritinib (80 mg/d for 4 weeks on 4 weeks off)

Patient 2

A 27-year-old male was diagnosed with low-risk APL in 2004. The patient achieved CR1 following induction therapy with ATRA (25 mg/m²/day, twice a day, day1∼ d28) combined with idarubicin (IDA, 8 mg/m², 3 days). Approximately a decade after the end of treatment, he relapsed in his bone marrow and CNS.CR2 was achieved after reinduction treatment with ATRA and ATO. In November of 2020, the patient complained of spinal discomfort. Examination of cerebrospinal fluid (CSF) showed abnormal promyelocytes were positive for PML/RARα and NGS identified WT1 and FLT3-TKD mutation, indicating central nervous system leukemia (CNSL), though BM showed mCR. He was then treated with intrathecal triple therapy (ITT, corticosteroid, Methotrexate, and Cytarabine) and ATO (0.16 mg/kg/d, d1∼d28) to prevent systematic relapse. The patient took no account of allo-HSCT for personal reasons, and then he chose Decitabine (20 mg/m²/d, 5 days), Venetoclax (100 mg d1, 200 mg d², 400 mg d3∼d28) plus Midostaurin (50 mg/d, twice a day, day 1∼28) for 3 cycles followed by Gilteritinib-based regimens for consolidation. Now he is in CR3 for 28 months with a normal life.

Patient 3

A 72-year-old male was diagnosed with Intermediate-risk APL in January 2021. Peripheral blood (PB) count revealed WBC was 8.16 × 10⁹/L, Hb was 7.6 g/dL, PLT was 12 × 10⁹/L and BM aspirates indicated the presence of promyelocytes. Induction therapy with low-dose HA and ATRA (25 mg/m²/day, twice a day, day 1 ∼ d28) resulted in CR1. However, after 20 months, the patient developed a headache and was diagnosed with CNSL. Further analysis confirmed the presence of FLT3-ITD both in BM and CSF. He was treated with ITT and ATO but showed no response. Then He received Gilteritinib (80 mg/d for 4 weeks on 4 weeks off) combined with ATRA (25 mg/m²/d for 2 weeks on 2 weeks off) and ATO (0.16 mg/kg/d for 4 weeks on 4 weeks off), which resulted in CR2. As the patient was unsuitable for allo-HSCT, two additional therapy cycles were conducted, resulting in sustained mCR.

Discussion

Among the 131 relapsed patients in the GIMEMA trial, 16 (12%) exhibited EMR, while in the European-PETHEMA, only 10 (6%) out of 139 relapses exhibited EMR. In both groups, the median time from CR to EMR was approximately 13 months, and the most frequent EMR sites were CNS (62.5% and 90%, respectively) and skin (19% and 10%, respectively), followed by middle ear (12.5%). Lung sites were only observed in the GIMEMA study at a rate of 6.2% [7,8]. In our cases, 2 patients’ EMR sites were CNS, and the other patient displayed EMR 3 times at different sites. EMR may occur in isolation or concurrently with bone marrow relapse [9]. In our cases, 2 patients’ EMRs were isolated and the other patient displayed both BMR and EMR at the same time.

Managing EMR in APL presents challenges due to the scarcity of information available. The first treatment option for EMR is local radiotherapy and surgical procedures [10]. High-dose cytosine arabinoside or ATO-based protocol for systemic therapy is always recommended followed by autologous or allogeneic hematopoietic stem cell transplant (HSCT) due to high incidence of concomitant hematological or molecular BM involvement [11–13]. However, in this study, three patients refused or were not eligible for allo-HSCT. Therefore, alternative therapies need to be investigated for durable complete remission.

Two FLT3 aberrations are relevant in APL. The most frequent is FLT3-ITD, occurring in 13–40% of APL patients [14]. The other aberration is a point mutation in the activation loop encoding region, typically in the codon for aspartic acid 835 (D835), which affects approximately 8% of APL patients [15]. FLT3-ITD mutations were associated with higher white blood cell counts (p < 0.0001), relapse-risk score (p = 0.0007), higher hemoglobin levels (p = 0.0004), higher frequency of the micro granular morphology (M3v) subtype (p = 0.03), and the short PML/RARA (BCR3) isoform (p < 0.0001). It is reported in an International Consortium on APL a study, FLT3-ITD^positive patients had a lower 3-year overall survival rate (62%) compared with FLT3-ITD^negative patients (82%) (p = 0.006) after a median follow-up of 38 months [16]. A meta-analysis also showed the proportion of patients with FLT3-D835 attaining remission was lower than that of patients with WT FLT3 (RR = 0.55, p < 0.001); The presence of the FLT3-D835 mutation also doubled the risk of death (RR of survival = 0.5; p = 0.029)[17].

In FLT3-mutant AML patients, FLT3 inhibitors have shown improved outcomes. The first-generation FLT3 inhibitor midostaurin was approved as a combination agent with standard chemotherapy in 2017 with evidence of improved survival in the SORAML study [18]. Gilteritinib, a highly selective and potent second-generation FLT3 inhibitor, showed superior remission rates and longer overall survival than conventional therapy and was approved for R/R AML patients with FLT3 mutations as the first single agent FLT3 inhibitor in Japan in 2018 [19]. Furthermore, some clinical cases reported the significant therapeutic effect of Gilteritinib to induce remission of EMR in AML patients with FLT3 mutation. Perrone et al. reported a relapsing medullar and meningeal AML patient with FLT3-ITD responding to Gilteritinib monotherapy [20]. Vignal et al. described objective sustainable responses and pharmacodynamic proofs of Gilteritinib CSF penetration in AML patients with CNSL [21]. Except for CNS infiltration, Kido et al. reported a FLT3-ITD mutated AML patients with isolated EMR in skin after HSCT achieved remarkable regression in the treatment of Gilteritinib [22].

Limited data have been reported for relapsed APL patients without HSCT. A study reported the four-year overall survival probability was 85% with a disease-free survival rate of 74% with prolonged ATRA-ATO therapy at the time of disease relapse [23]. In a 15-year prospective study, 73 patients with APL in first relapse were treated with oral ATO-based reinduction and consolidation, resulting 4-year LFS of 56.8%, with outcomes comparable to those with HSCT. But only 5 of 15 patients (33.3%) who had CNSL remained alive, which showed the worst OS in this cohort [24].

To the best of the authors’ knowledge, this is the first case series of successful treatment with Gilteritinib-based therapy in APL patients with EMR. Based on the FLT3 mutation, the patients were treated with a Gilteritinib-based therapy, resulting in a rapid and persistent complete regression of EMR. The successful diagnosis and treatment of our cases may provide a valuable experience for the therapy of EMR in APL patients. However, the efficacy of Gilteritinib as a single agent could not be assessed due to its use in combination with other regimens known as anti-APL effects. Though all three patients we reported achieved CR, the durability of the responses are needed to confirm in the future.

Conclusions

We reported three FLT3-mutant EMR APL patients both treated with Gilteritinib-based therapies, resulting in persistent complete regression of EMR, thus providing a valuable experience for further evaluation of the use of Gilteritinib in EMR APL patients.

Author contributions

Chunxiao Hou and Yu Chen collected data and wrote the manuscript. Yizhi Jiang and Shanhao Liu reviewed the manuscript and provided images. Dongping Huang and Suning Chen supervised the study and contributed to the manuscript preparation.

Ethics

The local ethics committee approved the study. Informed consent was obtained from the patients before study inclusion, in accordance with the Declaration of Helsinki. His record/information was anonymized and de-identified before analysis.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data supporting this study's findings are available from the corresponding author upon reasonable request.

Additional information

Funding

This work was supported by the Innovation Capability Development Project of Jiangsu Province under [grant number BM215004]; the Wuhu Science and Technology Research Project under [grant number 2022jc49]; and the Wannan Medical College school-level key project under [grant number WK2022ZF25].