Pretransplant FLT3/ITD status as a prognostic marker for outcome in FLT3-mutated AML

Internal tandem duplication (ITD) of the juxtamembrane domain of the FMS-like tyrosine kinase-3 (FLT3/ITD) gene is a common mutation detected in 30% of patients with acute myeloid leukemia (AML) and is associated with poor survival outcomes and high relapse rates. However, a recent study has shown that these negative effects are only seen if the ratio of mutated to normal alleles is > 0.5, which adds to the controversy of the role of allogenic-stem cell transplantation (allo-SCT) in FLT3-mutated patients in their first complete remission (CR1).¹

In a retrospective study, Grzegorz Helbig and colleagues from the Medical University of Silesia, Katowice, Poland, aimed to evaluate the potential factors that may have an impact on the outcome of FLT3-mutated patients after allo-SCT.¹

Study design and patient characteristics

• The study identified 43 adult patients with FLT3-mutated AML who were allografted between 2009–2019 from a database of medical records from the Medical University of Silesia
• After AML diagnosis, patients were treated according to the Polish Adult Leukemia Group protocol
• Induction therapy included daunorubicin, cytarabine, and cladribine
• Consolidative chemotherapy consisted of two cycles of mitoxantrone with cytarabine, or cytarabine alone for patients that achieved complete remission (CR)
• For patients with resistant disease after two inductions, three different salvage regimens were given according to the treating physician: CLAM (cladribine, cytarabine, and mitoxantrone), MEC (mitoxantrone, etoposide, and cytarabine), and FLAG-IDA (fludarabine, cytarabine, idarubicin, and granulocyte colony-stimulating factor [G-CSF])
• FLT3/ITD mutational analysis was performed using multiplex fluorescence-based PCR at diagnosis, before conditioning commencement, and at Day 30 after allo-SCT
• Patient characteristics are shown in Table 1 

Table 1. Patient characteristics¹

• 60% of patients had a normal diploid karyotype and the most common cytogenetic abnormality was trisomy 8 (9% of patients)
• No induction death occurred and 70% of patients achieved CR1, a further 9% achieved complete remission after reintroduction (CR2), and 21% of patients were transplanted in marrow aplasia
• Before transplant, 63% of patients had FLT3 measurable (minimal) residual disease (MRD) negativity
• The median time from diagnosis to transplant was 16.7 months

Results

• Acute graft-versus-host disease (GvHD) occurred in 58% of patients and chronic GvHD developed in 14% of patients
• Postallograft CR rate was 88%, with 65% of patients achieving FLT3/ITD negativity at Day 30 after allo-SCT
• Patients who were FLT3 MRD negative at transplant had a lower relapse incidence compared with those who remained FLT3 MRD positive (41% vs 59%; p = 0.01)
• Patients who eradicated FLT3/ITD mutation at Day 30 posttransplantation had a significantly lower relapse incidence than those who had detectable FLT3/ITD (23% vs 76%; p < 0.001).
• A strong positive correlation was shown between the posttransplant FLT3/ITD status and survival (r = 0.65; p < 0.001).
• At transplant, 28 patients had MRD data measured by flow cytometry (MRD-FC), which showed a strong positive correlation between FLT3 MRD positivity and MRD-FC positivity (r = 0.53; p = 0.03).
• The median overall survival (OS) and leukemia free survival (LFS) from allo-SCT were 28 months and 27 months, respectively
• The 2-year OS and LFS were 54% and 53%, respectively
• FLT3 MRD negativity at transplant prolonged LFS in multivariate analysis (HR, 5.3; 95% CI, 1.97–14.2; p < 0.001), whereas FLT3 MRD negativity and unrelated donor predicted a favorable OS (Table 2) 

Table 2. Univariate and multivariate analysis of risk factors for OS and LFS¹

Conclusion

The strong positive correlation between FLT3 MRD positivity and MRD-FC positivity suggests that pretransplant detection of the FLT3/ITD mutation by PCR may serve as a reliable MRD marker and predict posttransplant outcome, particularly LFS, better than hematological disease status.

The authors note that although the study was limited by the small sample size, the results are in-line with other published studies. However, they suggest that further studies with larger numbers of patients are needed to draw final conclusions.