High expression of c-kit mRNA predicts unfavorable outcome in adult patients with t(8;21) acute myeloid leukemia

Abstract

The reason that a certain subgroup of acute myeloid leukemia (AML) patients with t(8;21) translocation (generating the AML1/ETO fusion gene) displays a poor survival remains elusive. The proto-oncogene c-kit is expressed in approximately 80% of AML cases. The kinase domain mutation of the c-kit gene, one of the most common gain-of-function mutations associated with t(8;21) AML, predicts higher relapse risk and poor prognosis. However, the role of c-kit high expression in t(8;21) AML remains poorly understood. Here we evaluated the prognostic significance of c-kit expression levels in AML patients. The mRNA expression of c-kit was determined by real-time quantitative reverse transcription PCR in 132 adult AML patients. Patients were grouped into quartiles according to c-kit expression levels (Q1-Q4, each quartile containing 25% of patients) and divided into c-kit high (Q4; n = 33) and c-kit low (Q1-Q3; n = 99). High c-kit expression was associated with AML1/ETO-positive and with c-kit mutation. Of note, 35.8% of the AML1/ETO-positive AML patients carrying wild-type c-kit expressed high levels of c-kit, suggesting that other factors are involved in c-kit overexpression. High c-kit expression was associated with inferior overall and event-free survival in AML1/ETO-positive patients and was independently predictive for overall and event-free survival in multivariate analyses in a c-kit mutation-independent manner. Thus, high c-kit expression serves as a reliable molecular marker for poor prognosis, supporting a pathogenetic role of c-kit signaling in AML1/ETO-positive AML. AML1/ETO-positive patients with high c-kit expression might benefit from early treatment modifications and molecular target therapies.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1. Selective high expression of c-kit in AML1/ETO-positive AML cell lines and patients.

(A) qPCR showing c-kit expression in myeloid leukemia cell lines. CML-BC: chronic myeloid leukemia in blast crisis. Bars indicate the mean±SEM from three independent experiments. ABL1 levels were measured for normalization. (B) Normalized c-kit expression in pretreatment samples of 461 patients with de novo AML (GEO database, GSE6891). The gene expression was determined using gene-expression arrays (Affymetrix HGU133 Plus 2.0 GeneChips), which reflected by the intensity of hybridization of labeled mRNA to the gene chip. Median values are depicted by the horizontal lines. The Mann-Whitney U test was used to compare expression levels between groups. (C) qPCR showing c-kit expression level in bone marrow samples from untreated AML patients at diagnosis and healthy donors. ABL1 levels were measured for normalization. Median values are depicted by the horizontal lines. The Mann-Whitney U test was used to compare expression levels between groups.

Fig 2. Positive correlation between AML1/ETO and c-kit expression levels in AML1/ETO-positive AML.

(A) The patients described in Fig 1C were divided into high and low c-kit expression groups, which described in detail in statistical analysis. The threshold is depicted as a dashed line. Patient characteristics are described in Table 1. (B) Stratification of AML1/ETO-positive AML patients with high and low c-kit expression according to c-kit mutation status. (C) Correlation between c-kit and AML1/ETO levels in AML1/ETO-positive AML patients was assessed by the Spearman rank correlation coefficient. Gene expression was detected by qPCR. ABL1 levels were measured for normalization. Black circles indicate AML patients carrying wtc-kit.

Fig 3. Higher expression of c-kit in AML1/ETO-positive AML predicts more inferior prognosis.

(A-C) Kaplan-Meier estimate for OS and EFS in indicated patient subgroups. Survival curves were compared using log-rank test.