Epigenetic instability and aberrant repression of tumor suppressor genes are fundamental aspects of acute myeloid leukemia (AML) biology. Current prognostic assays for AML focus on the genetic aspects of disease biology, for example, chromosome abnormalities and recurrent mutations. We hypothesized that a simple assay for an epigenetic abnormality can address the epigenetic domain of AML, with implications for prognostication and for treatment selection with chromatin relaxing drugs. We focused on patients with intermediate risk cytogenetics (CG) and evaluated the association between histone (H4) acetylation and complete remission (CR), relapse-free survival (RFS), and overall survival (OS) in newly diagnosed AML patients with intermediate risk CG.
We assessed histone H4 acetylation status in bone marrow biopsies from newly diagnosed AML patients with intermediate risk CG treated at our institution between the years 2003–2005. CG risk group was ascribed per Cancer and Leukemia Group B criteria. Association with CR, RFS and OS was assessed using logistic regression and Cox proportional hazard regression models. Variables used in the multivariate models included: age, WBC at diagnosis, gender, and history of antecedent hematologic disorder (AHD). B5-fixed bone marrow core biopsies were reviewed for areas with the highest blast concentration. Immunohistochemistry was performed for acetyl-H4 (1:200 dilution; polyclonal; Upstate Biotech, Lake Placid, NY) using automated stainers and heat-induced epitope retrieval. In each case, five hundred blasts were counted and only strong nuclear staining was classified as positive. Based on the distribution of cell counts, cases were classified as strongly positive if nuclear staining occurred in > 80% of the blasts.
Forty-two patients had intermediate risk CG and received cytarabine-based induction chemotherapy. The median age was 56.5 years (range 17–79) and median WBC count at diagnosis was 10.9 × 109/L (range 0.8– 227.9). Twenty two percent of patients had an AHD. Thirty three patients (78%) had normal cytogenetics. Chromosomal abnormalities +8,+21, and 11q23 abnormalities were present in 3 (7.1%), 1 (2.3%) and 4 (9.4%) patients, respectively. FLT3 status was available on only 9 patients; with 7 patients having no FLT3 mutations. Twelve patients (28.5%) received an allogeneic bone marrow transplant in first remission. The median follow-up time was 22.4 months (range 0.6–65.3). Thirty-four patients (81%) achieved CR. Using the 80% cut-off, 15 patients (35.7%) were positive for histone H4 acetylation. Histone (H4) acetylation was not associated with achievement of CR (OR=3.0, 95% CI 0.3–25.3, p=0.3). However, on multivariate analysis, a significant association was found between histone acetylation and risk of relapse (HR 0.34, 95% CI 0.11–0.99, p=0.05) and overall survival (HR=0.34, 95% CI 0.15–0.80, p=0.01). Inclusion of allogeneic transplant in the multivariate models did not change these estimates.
Histone H4 acetylation is associated with improved RFS and OS in newly diagnosed AML patients with intermediate risk CG. These results will need to be validated in a larger population of uniformly treated patients. However, histone H4 acetylation has the potential as a simple assay to assess for the contribution of abnormal epigenetics to AML biology, with prognostic and potentially therapeutic implications, given the increasing role of epigenetically targeted therapy in myeloid malignancy management.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.