Expression of Phosphorylated Signal Transducer and Activator of Transcription 5 (pSTAT5) Is Associated with An Increased Risk of Death In Acute Myeloid Leukemia.

Acute myeloid leukemia (AML) is characterized by rapid growth, resistance to therapy, and poor overall survival. Clinical and biologic prognostic markers can help define pathogenesis, guide treatment, and identify novel therapies. Phosphorylated signal transducer and activator of transcription 5 (pSTAT5) is one such potential marker. The transcription factor STAT5 regulates many aspects of cell growth, survival, and differentiation. Constitutive activation of STAT5 (by phosphorylation) has been identified in a number of malignancies, including AML. We investigated whether the level of pSTAT5 expression correlates with complete remission (CR) rates, progression-free survival (PFS), and overall survival (OS) in patients (pts) with newly diagnosed AML.

From 1999 to 2005, all adult pts with newly diagnosed AML (WHO criteria) receiving induction chemotherapy and with an available diagnostic bone marrow biopsy performed at our institution were evaluated. B5-fixed bone marrow core biopsies were reviewed for areas with the highest concentration of blasts. A tissue microarray was constructed using 1 mm cores. The cores were arrayed in duplicate in the majority of samples. Immunohistochemistry was performed for pSTAT5 with anti-pSTAT5 a/b Y695/99 mouse monoclonal antibody (AX1; Advantex Bioreagents) using automated stainers and heat-induced epitope retrieval. In each case, five hundred blasts were counted. The percentage of cells staining positive for pSTAT5 expression was determined by a pathologist blinded to clinical results. Standard metaphase karyotypes were classified into cytogenetic (CG) risk groups by CALGB criteria. Cox proportional hazards analysis was used to identify univariate and multivariate prognostic factors for CR, PFS, and OS, including age at diagnosis, history of an antecedent hematologic disorder (AHD), WBC at diagnosis, pSTAT5 expression, and CG risk group.

Adequate tissue and clinical data were available in 112 pts. The median age was 57 years, and median WBC at diagnosis 12.0 K/ μL. Twenty six percent of pts had favorable CG, 41% intermediate risk, 27% high risk, and 6% other (unknown or could not be classified). Nineteen percent of pts had an AHD. pSTAT5 expression was absent in 58% of pts. The remainder of the pts had: 1–5% pSTAT5 (25% of pts), 10% pSTAT5 (11% of pts), 20% pSTAT5 (4% of pts), 30% pSTAT5 (1% of pts), and 50% pSTAT5 (2% of pts). Seventy percent of all pts achieved a CR following induction chemotherapy. Sixty-four percent of pts received post-remission chemotherapy, 3.6% an autologous transplant, and 13.6% an allogeneic transplant in first CR. Median PFS and OS were 9.6 months and 16.0 months, respectively. On univariate analysis, age, history of AHD, WBC at diagnosis, CG risk, and any pSTAT5 expression were prognostic factors for PFS and OS. In multivariable analyses controlling for the above prognostic factors, pSTAT5 expression > 0 was also significantly associated with an increased risk of death (HR 1.96, 95% CI 1.19–3.23, p=0.008), progression or death (HR 1.64, 95% CI 1.01–2.66, p=0.046), and relapse after achieving CR (HR 2.31, 95% CI 1.16–4.63, p=0.018). pSTAT5 expression was not a predictor of achievement of CR.

pSTAT5 expression in newly diagnosed adults with AML is associated with a decreased PFS, decreased OS, and increased risk of relapse. Validation of its prognostic value requires additional study. Agents targeting this signaling pathway might improve the outcome of pts with AML.

No relevant conflicts of interest to declare.