Immunohistochemical Expression of CD123 Is Associated with an Inferior Clinical Outcome in Acute Myeloid Leukemia

Background:

The aberrant expression of the interleukin-3 receptor (IL3RA or CD123) alpha chain is frequently observed in a subset of leukemic disorders, including acute myeloid leukemia (AML), particularly in leukemia stem cells. Using flow cytometric (FCM) analysis, studies have shown that increased CD123 expression is associated with a poor prognosis of AML. Although FCM is a sensitive technique, the analysis may be limited in a clinical setting because live leukemia cells are required. Immunohistochemistry (IHC) is a more useful alternative compared with FCM because it can be tested long after specimens are collected; however, it is less sensitive. Here we evaluated the impact of blast CD123 expression via IHC analysis for the prognosis of AML.

Patients and methods:

This study was performed as a retrospective analysis of 70 patients who were diagnosed with de novo AML (M0-M5, n = 48) and AML with myelodysplasia-related changes (MRC) (n = 22) at our hospital from February 2008 to September 2015. The median age at diagnosis was 64.5 years (range: 21-93 years). The median follow-up period was 498 days (range: 2-3052 days). Morphological findings were obtained using HE stains of 3-µm sections. Formalin-fixed, paraffin-embedded specimens were used for immunohistochemical analysis. We analyzed the relationships between the patients' clinical outcome and CD123, p53, CD34, CD71, CD56, and c-kit expressions. [(CD123, CD34, CD71, CD56, and c-kit immunostained slides were defined as positive if >10% of the blast cells had a moderate to strong membranous staining. p53 was evaluated as positive when more than 5% of the cells were positively stained. For each case, the following data were obtained: patient age (>60 years or <60 years), sex, karyotype (good, intermediate, or poor), SCT (undergone or not), 1st induction (failure or complete remission (CR), and overall survival (OS)].

Results:

Of the 70 cases, percentages of the positive immunohistochemical study dates were as follows: CD123: 25.7%; p53: 30%; CD34: 52.8%; CD71: 46.3%; CD56: 25.7%; and c-kit: 77.1%. There were 48 cases with de novo AML: CD123: 29.1%; p53: 75%; CD34: 52%; CD71: 37.5%; CD56: 27%; and c-kit: 79.1%. Moreover, there were 22 cases with MRC: CD123: 18.1%; p53: 31.8%; CD34: 54.5%; CD71: 66.6%; CD56: 22.7%; and c-kit: 72.7%. CD71 is highly expressed in MRC than de novo AML (P = 0.036). Among all patients, the CR rate following first induction therapy was 62.3%. Age (≥60 years), high p53 expression, disease (MRC), and poor karyotype were associated with induction failure (P = 0.011, P = 0.002, P <0.001, and P = 0.008, respectively). Among patients with de novo AML, only elevated CD123 expression was associated with the failure to obtain a CR following the first remission induction chemotherapy (P = 0.044). In contrast, among patients with MRC, CD123 expression was not associated with any clinical data or the CR rate. The 2-year OS rates were 45.9%. Age (≥60), high p53 expression, MRC, poor karyotype were significantly associated with poor OS (P = 0.003, P = 0.036, P <0.001, and P = 0.002, respectively). In Multivariate analysis, age (≥60 years), MRC, poor karyotype are significantly associated with poor OS (P = 0.028, P = 0.001, and P = 0.014, respectively). Among de novo AML patients, CD123 expression, p53 expression, and induction failure were independently associated with poor OS (P = 0.036, 0.003 and P < 0.001, respectively), and increased p53 expression and induction failure was associated with poor OS in the multivariate analysis (P = 0.001 and P = 0.002). Among patients with MRC, only induction failure was associated with the OS (P = 0.026).

Conclusion:

This is the first study to demonstrate that CD123 expression using IHC is associated with poor a CR rate and OS in de novo AML patients; however, this association was not observed in MRC patients. Our results suggest that CD123 expression may predict the refractory to induction therapy and poor OS in de novo AML. Moreover, these results support previous reports using FCM. Therefore, CD123 expression may become one of the important factors used to characterize leukemia blasts and predict the prognosis of AML. In addition, novel therapy with antibodies targeting CD123 is currently under development. Therefore, we suggest that an analysis of CD123 expression using IHC is a clinically important assessment for de novo AML patients at the time of diagnosis.