Acute Myeloid Leukemia with an FMS-like Tyrosine Kinase 3-tyrosine Kinase Domain Mutation Developing Gilteritinib-induced Differentiation Syndrome

Abstract

FMS-like tyrosine kinase 3 (FLT3) mutations are observed in 30% of acute myeloid leukemia (AML) cases and indicate a poor prognosis. FLT3 inhibitors, such as gilteritinib, improve outcomes but may cause differentiation syndrome (DS) in approximately 3% of patients. We herein report a case of FLT3-tyrosine kinase domain-mutated AML treated with idarubicin and cytarabine, followed by a single dose of gilteritinib. The patient developed DS that required intubation. Initial steroid therapy was ineffective; however, steroid pulse therapy and additional idarubicin resolved the DS. This case shows that gilteritinib-induced DS can occur early and severely and requires prompt and aggressive management.

Introduction

Acute myeloid leukemia (AML) remains associated with poor long-term outcomes and survival rates, despite significant improvements in AML treatment. Approximately 30% of AML patients harbor mutations in FMS-like tyrosine kinase 3 (FLT3), a receptor tyrosine kinase involved in activating multiple downstream growth signals (1,2). Most FLT3 mutations are internal tandem duplications (ITDs) within the juxtamembrane domain, and a minority are point mutations within the tyrosine kinase domain (TKD) (2). Patients with FLT3-ITD have poorer clinical outcomes than those with wild-type FLT3, but the prognostic significance of FLT3-TKD remains unclear (3,4).

Recently, FLT3 inhibitors have emerged, which have contributed to improving the prognosis of FLT3-mutated AML and have become indispensable in treatment (5-7). FLT3 inhibitors are classified into two types based on their mechanism of action. Type I inhibitors bind to FLT3 in the active conformation near the activation loop or the adenosine triphosphate (ATP) binding site and are active against ITD and mutant TKD, as typified by midostaurin, sunitinib, lestaurtinib, crenolanib, and gilteritinib (8). Type II inhibitors, such as sunitinib, sorafenib, and quizartinib, bind FLT3 in an inactive state near the ATP-binding domain, targeting FLT3-ITD but not mutant TKD (8).

Differentiation syndrome (DS) is a well-known complication of all-trans-retinoic acid (ATRA) and arsenite (ATO) treatment in acute promyelocytic leukemia (APL). The etiology of DS in APL is not fully understood, but it may be due to the release of inflammatory cytokines, such as interleukin-6 (IL6), IL8, and tumor necrosis factor-alpha, from APL cells differentiated by ATRA/ATO, causing systemic inflammatory response syndrome (9). Recently, DS has been reported in AML other than APL because of the use of new molecular-targeted drugs, such as FLT3, isocitrate dehydrogenase, and menin inhibitors (10,11).

We herein report a patient who developed DS after administration of the type I FLT3 inhibitor gilteritinib during initial induction therapy for FLT3-TKD-mutated AML.

Case Report

A 59-year-old woman was referred to our hospital after a routine medical examination revealed anemia, thrombocytopenia, and leukocytosis. She had undergone surgery for right breast cancer stage IIB five years prior and received four courses of fluorouracil, epirubicin, and cyclophosphamide, followed by four courses of docetaxel and trastuzumab as postoperative chemotherapy. A blood examination revealed a hemoglobin level of 8.1 g/dL, platelet count of 69×10⁹/L, and white blood cell (WBC) count of 36.9×10⁹/L (79% myeloblasts, 5% neutrophils). Bone marrow puncture revealed hypercellular bone marrow (nucleated cell count, 172×10⁹/L), and myeloblasts accounted for 79.6% of nucleated cells (Fig. 1A, B). Flow cytometry showed that myeloblasts were positive for CD7, CD13, CD33, CD34, CD117, and myeloperoxidase. A chromosomal analysis revealed 7q deletion. Based on these results, the patient was diagnosed with myelodysplasia- and post-cytotoxic therapy-related AML.

Figure 1.

A: Bone marrow puncture at the diagnosis. Myeloblasts were observed in 79.6% of patients. B: Positive for peroxidase staining.

The clinical course of the patient is shown in Fig. 2. The patient was initially treated with a combination of idarubicin (IDR; 12 mg/m², days 2-4) and cytarabine (AraC; 100 mg/m², days 1-7) as induction chemotherapy. During the treatment course, she tested positive for the FLT3-TKD mutation (allele ratio, 1.30). On day 7, 1% of the blasts remained in the peripheral blood, and she was considered refractory; therefore, gilteritinib 120 mg/day was started on day 8. On the same day, she developed a fever, gained weight, and required supplemental oxygen. A blood examination revealed that the WBC count had decreased to 2.2×10⁹/L on day 7 but increased to 4.0×10⁹/L on day 9. Blast cells in the peripheral blood disappeared, but neutrophils accounted for 74%, and immature cells, such as myelocytes and promyelocytes, also appeared. Bone marrow puncture revealed that the nucleated cell count was 11×10⁹/L, and blast cells had disappeared; however, mature neutrophils with atypia, such as nuclear segmentation abnormality and Pelger nuclear abnormalities, accounted for 64% of the cells (Fig. 3). Computed tomography (CT) showed no obvious foci of infection but revealed cardiac enlargement and bilateral pleural effusion.

Figure 2.

The clinical course of differentiation syndrome. IDR: idarubicin, AraC: cytarabine, mPSL: methylprednisolone, WBC: white blood cell, Neut: neutrophil

Figure 3.

Bone marrow puncture on day 9. Myeloblasts disappeared, but neutrophil abnormalities, such as Pelger’s nuclear abnormalities, were observed.

We suspected DS, discontinued gilteritinib on day 9, and started methylprednisolone at 1 mg/kg. However, her respiratory condition rapidly worsened on day 12 and her weight increased by 5.9 kg. Chest radiography and CT showed bilateral moderate pleural effusion, extensive infiltrates in the lower lobes of both lungs, and ground-glass opacity (Fig. 4A, B). A blood examination revealed that the WBC count had increased to 5.6×10⁹/L, of which 76% were neutrophils with atypia, indicating exacerbation of DS. Following the treatment strategy for refractory DS in APL, she was treated with steroid pulse therapy (1 g/day) and additional IDR.

Figure 4.

A: Chest X-ray on day 12. Opacity of bilateral lung fields appeared. B: CT on day 12. Bilateral pleural effusion, infiltrative shadows and cardiac enlargement were observed. C: Chest X-ray on day 17. The opacity of the bilateral lung fields was improved.

She was intubated and ventilated as her respiratory status worsened. An arterial blood gas analysis before intubation showed a pH of 7.31, pCO₂ of 58.3 mmHg, and pO₂ of 95.0 mmHg under 15 L of oxygen with a reservoir mask, indicating diffusion impairment. Infectious pneumonia could not be ruled out; however, no significant bacteria were detected in the blood or sputum cultures. As a precaution, the patient was treated with full antibacterial and antifungal agents. She responded quickly to treatment, with her respiratory condition improving and her WBC count decreasing. The steroids were gradually tapered after three days of steroid pulse therapy. Her respiratory condition further improved over time, and she was extubated on day 17 (Fig. 4C). Peripheral blood testing performed on day 12, when blast cells had disappeared, revealed a positive FLT3-TKD mutation (allelic ratio 1.21), which was consistent with DS. After hematopoietic recovery, a bone marrow examination was performed on day 34, which showed hypoplastic bone marrow with a nucleated cell count of 4.0×10⁹/L, but the blast cell count was 3.2%, indicating hematologic remission. However, flow cytometry showed that the same abnormal phenotype remained in approximately 3% of the cell population (co-expression of CD7 and CD33) at the primary diagnosis, and a chromosomal analysis showed residual 7q deletion. After a treatment course with venetoclax and azacitidine, she underwent allogeneic peripheral blood stem cell transplantation from her human leukocyte antigen-haploidentical daughter and has since remained alive in complete donor chimerism.

Discussion

The expression of PU.1 and CCAAT/enhancer-binding protein α (C/EBPα) is important for differentiating myelomonocytic cells (12). In wild-type FLT3 cell lines, granulocyte colony-stimulating factor (G-CSF) treatment induced the expression of PU.1 and C/EBPα, but G-CSF treatment neither induced the expression of C/EBPα or PU.1 nor induced differentiation into granulocytic cells in FLT3-ITD mutation-positive cell lines. Two of three patients with FLT3-ITD mutation-positive AML treated with FLT3 inhibitors showed restoration of C/EBPα and PU.1 expression. Granulocyte lineage marker expression was also observed in these patients, supporting the idea that FLT3 inhibitors induce myeloid differentiation.

The response to gilteritinib treatment can be divided into one with and without differentiation (13). In cases of response without differentiation, bone marrow cellularity decreased with a decrease in blast cells, and the FLT3 allelic burden also decreased. In cases of a response with differentiation, bone marrow cellularity was stable with marked left-shifted granulocytic hyperplasia, and the FLT3 frequency remained stable. In addition, a similar response has been observed with quizartinib, a type II inhibitor (14). The quizartinib trial identified normal cytogenetics and the presence of FLT3-ITD, DNA (cytosine-5)-methyltransferase 3 alpha mutation, and nucleophosmin mutation as the types most likely to cause a differential response, while the gilteritinib trial did not identify any factors that could predict the response type. PU.1, or C/EBPα expression in relation to FLT3-TKD mutations has not been reported, but the above reports of a response with differentiation included cases with FLT3-TKD, and it is expected that similar responses will occur with FLT3 inhibitors in cases with FLT3-TKD mutations.

Based on clinical studies of FLT3-mutated relapsed and refractory AML, the incidence of DS was 3% (11/319 gilteritinib-treated patients), and the time to the DS onset ranged from 2 to 75 days (10,15). Of the 11 patients, 9 improved with steroid and gilteritinib discontinuation (1 fatal episode of DS). In other studies, most cases seem to have improved with steroid and FLT3 inhibitor discontinuation, as summarized in Table (13,16,17). In addition, when FLT3 inhibitors are used in remission induction chemotherapy, the tumor volume is expected to be reduced after cytotoxic chemotherapy, and DS should be easier to control. Cases of DS observed with midostaurin and quizartinib in combination with chemotherapy have not yet been reported (18).

Table.

Summary of Previous Reports of FLT3 Inhibitor-induced DS.

	case 1	case 2	case 3	case 4
FLT3-ITD or TKD	FLT3-ITD	FLT3-TKD	FLT3-ITD	unknown
up to the onset of DS (days)	15	89	180	56
clinical events	fever, hypotention, pleuritic chest pain, increased WBC	hypoxia, rash	fever, body weight gain, dyspnea with interstitial pulmonary infiltrates, increased WBC, elevated serum creatinine	hypoxia, diffuse ground glass opacifications
discontinuation of gilteritinib	continued	for 2 days, then restarted	for 40-50 days, then restarted	discontinued, it is not known whether gilteritinib was restarted
treatment	steroid	steroid	low-dose AraC, mitoxantrone	steroid
until improvement	5 days	discharged few days later on steroid taper	10-20 days	discharged on day 6
references	(13)	(13)	(16)	(17)

FLT3: FMS-like tyrosine kinase 3, ITD: internal tandem duplication, TKD: tyrosine kinase domain, DS: differentiation syndrome, WBC: white blood cell, AraC: cytarabine

Dexamethasone is reported to be initiated promptly at the first sign of suspected DS, and targeted therapy was discontinued if the patient showed no response to dexamethasone or had severe DS, regardless of APL or AML (9,10,15). However, gilteritinib has a long half-life of 113 h (compared with ATRA 1-2 h and ATO 10-17 h), and treatment discontinuation may not lead to prompt symptomatic improvement (10).

In addition, leukocytosis is common with DS, and cytoreductive management, such as hydroxyurea, gemtuzumab ozogamicin, or AraC, is recommended if the WBC count is ＞25×10⁹/L to prevent further side effects from DS (15).

In the present case, DS was not controlled by the initial therapeutic dose of steroids and gilteritinib discontinuation. The blasts in the peripheral blood and bone marrow appeared to disappear after IDR/AraC administration, but abnormal clones remained. This is a case of differentiation response, and differentiation may have been induced by gilteritinib. The FLT3 mutation allele ratio remained unchanged between the time of initial onset and the onset of the differentiation syndrome. Furthermore, gilteritinib was administered for only 1 day, and the long half-life of gilteritinib may have prolonged its effect, resulting in prolonged DS.

This case highlights that even a single dose of gilteritinib during induction therapy can provoke severe DS that requires aggressive intervention, emphasizing the need for early recognition and management.

The authors state that they have no Conflict of Interest (COI).