Integration of gene mutations in risk prognostication for patients receiving first-line immunochemotherapy for follicular lymphoma

Background: Follicular lymphoma (FL) is a clinically and genetically heterogeneous disease. The prognostic value of somatic mutations has not been systematically evaluated and no genetic factors have been identified that distinguish patients at highest risk of treatment failure. Methods: We performed deep sequencing of 74 genes in 151 patients treated with R-CHOP from a phase III trial. Mutations and clinical factors were incorporated into a risk model using multivariable L1-penalized Cox regression. We validated the risk model in an independent cohort of 107 patients treated with R-CVP. Results: The final clinicogenetic index, the “m7-FLIPI”, contained the FL International Prognostic Index (FLIPI), ECOG performance status, and mutation status of 7 genes (EZH2, ARID1A, MEF2B, EP300, FOXO1, CREBBP and CARD11). In the training cohort, the m7-FLIPI defined a high-risk group (28% of patients) with 5-year failure-free survival (FFS) of 38% vs 77% for the low-risk group (Hazard ratio (HR) 4.1, confidence Interval (CI)=[2.5;6.9], p<0.0001). In the validation cohort, the m7-FLIPI defined a high-risk group (22% of patients) with 5-year FFS of 25% versus 68% (HR 3.6, CI=[2.0;6.4], p<0.0001) in the low-risk group. In both cohorts, the m7-FLIPI outperformed the FLIPI alone. Strikingly, all 66 patients with EZH2 mutations in both cohorts were categorized as low-risk m7-FLIPI, and EZH2 mutations defined a distinct transcriptional profile. Conclusions: The combination of clinical factors and mutations in 7 genes can identify the subset of patients with FL at highest risk of treatment failure. The m7-FLIPI can be widely utilized for risk prognostication and patient stratification. All RNA samples were derived from formalin-fixed paraffin-embedded tissue blocks and processed using the Illumina Whole-Genome DASL assay. The study includes 138 gene expression samples from the BC Cancer Agency cohort, 106 of which are from patients that were used in the final validation cohort of the clinicogenetic risk model.