Proteomic Analysis Identifies Outcome-Predictive Clusters in Patients with Peripheral T-Cell Lymphoma, Not Otherwise Specified

Introduction: Peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS) is a heterogeneous group of mature T-cell lymphomas, probably composed by different biologically related subsets that have not yet been conclusively identified. In the WHO classification, PTCL-NOS accounts for 25-30% of all mature T-/NK-cell malignancies. The clinical outcome is generally poor with a 5-yr overall survival of 30-35% after conventional treatment strategies. The aim of the study was to apply proteomic analysis in PTCL-NOS and to use the protein expression profiles to characterize clinically relevant subsets within this heterogeneous entity by means of unsupervised cluster analysis.

Methods: Archival frozen tumor tissue samples from 20 patients diagnosed with PTCL-NOS from 1991 to 2010 were analyzed for protein expression by high-resolution two-dimensional gel electrophoresis. Individual protein spots were visualized with fluorescence staining and the expression profiles were identified. All patients were homogeneously treated with curatively intended anthracycline-containing combination regimens. Clinico-pathological features were obtained from the Danish Lymphoma Registry (LYFO) and from patient records. Hyperplastic tonsils from healthy adults were included as reference tissue (n=8). Principal component analysis and unsupervised hierarchical cluster analysis were performed on the basis of the protein expression profiles. Differentially expressed (two-fold or higher, Mann-Whitney U-test) proteins between the detected clusters were identified by liquid chromatography - tandem mass spectrometry.

Results: Unsupervised cluster analysis defined three distinct clusters: one containing all reference samples and two additional ones further subdividing the PTCL-NOS cases in two separate subsets. Patients from these two PTCL-NOS subsets had significantly different responses to treatment and survival (p = 0.001). The differentially expressed proteins were primarily involved in (i) promotion of tumor growth, (ii) regulation of cellular metabolism, and (iii) immune responses.

Conclusion: Proteomic analysis identified shared protein expression patterns and potential prognostic markers in subsets of PTCL-NOS.