Cellular histone modification patterns predict prognosis and treatment response in resectable pancreatic adenocarcinoma: results from RTOG 9704

Abstract

PURPOSE Differences in cellular levels of histone modifications have predicted clinical outcome in certain cancers. Here, we studied the prognostic and predictive value of three histone modifications in pancreatic adenocarcinoma. METHODS Tissue microarrays (TMAs) from two pancreatic adenocarcinoma cohorts were examined, including those from a 195-patient cohort from Radiation Therapy Oncology Group trial RTOG 9704, a multicenter, phase III, randomized treatment trial comparing adjuvant gemcitabine with fluorouracil and a 140-patient cohort of patients with stage I or II cancer from University of California, Los Angeles Medical Center. Immunohistochemistry was performed for histone H3 lysine 4 dimethylation (H3K4me2), histone H3 lysine 9 dimethylation (H3K9me2), and histone H3 lysine 18 acetylation (H3K18ac). Positive tumor cell staining for each histone modification was used to classify patients into low- and high-staining groups, which were related to clinicopathologic parameters and clinical outcome measures. Results Low cellular levels of H3K4me2, H3K9me2, or H3K18ac were each significant and independent predictors of poor survival in univariate and multivariate models, and combined low levels of H3K4me2 and/or H3K18ac were the most significant predictor of overall survival (hazard ratio, 2.93; 95% CI, 1.78 to 4.82) in the University of California, Los Angeles cohort. In subgroup analyses, histone levels were predictive of survival specifically for those patients with node-negative cancer or for those patients receiving adjuvant fluorouracil, but not gemcitabine, in RTOG 9704. CONCLUSION Cellular levels of histone modifications define previously unrecognized subsets of patients with pancreatic adenocarcinoma with distinct epigenetic phenotypes and clinical outcomes and represent prognostic and predictive biomarkers that could inform clinical decisions, including the use of fluorouracil chemotherapy.

Fig 1.

CONSORT diagram of patients in Radiation Therapy Oncology Group (RTOG) trial RTOG 9704 undergoing analysis of histone modifications. FU, fluorouracil; TMA, tissue microarray.

Fig 2.

Cellular heterogeneity of histone modifications in pancreatic adenocarcinoma. (A) Representative immunohistochemistry for histone modifications at ×10 or ×40 (inset) objective from tumors of either low-grade (ie, patient 1) or high-grade (ie, patient 2) histology. The distribution of tumors according to indicated percentage of tumor cells with positive nuclear staining is shown for each histone modification in the (B) Radiation Therapy Oncology Group study 9704 or (C) University of California, Los Angeles stages I and II tissue microarray.

Fig 3.

Overall patient survival in the University of California, Los Angeles stages I and II pancreatic cancer tissue microarray (TMA) on the basis of indicated histone modification group. Kaplan-Meier plots visualize survival probabilities for the high-level (blue line) versus low-level (gold line) histone group for (A) H3K4me2, (B) H3K18ac, (C) H3K9me2, and (D) low H3K4me2 and/or H3K18ac versus high H3K4me2 and H3K18ac. P values are for log-rank tests.

Fig 4.

Overall survival in Radiation Therapy Oncology Group trial RTOG 9704 tissue microarray for indicated histone modification after first stratifying on treatment arms. Patients were stratified on the basis of adjuvant chemotherapy: (A, B) fluorouracil; (C, D) gemcitabine. Kaplan-Meier plots then were used to visualize survival probabilities for patients with either high (blue line) or low (gold line) levels of (A, C) H3K4me2 or (B, D) H3K9me2. P values are for log-rank tests.

Fig A1.

(A, C, E) Overall and (B, D, F) disease-free survival for all patients in the Radiation Therapy Oncology Group trial RTOG 9704 tissue microarray. Kaplan-Meier plots are used to visualize differences in survival probabilities for the high (blue line) versus low (gold line) level group for either (A, B) H3K4me2, (C, D) H3K9me2, or (E, F) H3K18ac. P values are for log-rank tests.

Fig A2.

(A, C, E) Overall and (B, D, F) disease-free survival in Radiation Therapy Oncology Group trial RTOG 9704 comparing gemcitabine (blue line) or fluorouracil (FU, gold line) in the subgroup of patients with low levels of either (A, B) H3K4me2, (C, D) H3K9me2, or (E, F) H3K18ac. Median survival time (MST) with 95% CI for each treatment is indicated, as well as P values from log-rank tests.