Follicular lymphoma comprises germinal center-like and memory-like molecular subtypes with prognostic significance

• RNAseq identifies MEM-like and GC-like FL subtypes related to cell-of-origin, with specific mutational profiles and clinical outcomes.

• IHC can be routinely used to identify MEM-like patients with adverse PFS, who could benefit from treatments other than R-chemotherapy.

A robust prognostic and biological classification for newly diagnosed follicular lymphoma (FL) using molecular profiling remains challenging. FL tumors from patients treated in the RELEVANCE trial with rituximab-chemotherapy (R-chemo) or rituximab-lenalidomide (R2) were analyzed using RNA-sequencing, DNA-sequencing, immunohistochemistry (IHC) and/or fluorescence in situ hybridization. Unsupervised gene clustering identified two gene expression signatures (GS) enriched with normal memory (MEM) B-cells and germinal center (GC) B-cells signals, respectively. These two GS were combined into a 20-genes predictor (FL20) to classify patients into MEM-like (n=160) or GC-like (n=164) subtypes, which also displayed different mutational profiles. In the R-chemo arm, MEM-like patients had significantly shorter progression free survival (PFS) than GC-like patients (HR=2.13; p=0.0023), and this prognostic correlation remained significant in a multivariable model including FLIPI (p=0.005). In the R2 arm, both subtypes had comparable PFS, demonstrating a R2 benefit over R-chemo for MEM-like patients (HR=0.54; p=0.011). The prognostic value of FL20 was validated in an independent FL cohort with R-chemo treatment (GSE119214 (n=137)). An IHC algorithm (FLCM) using FOXP1, LMO2, CD22 and MUM1 antibodies was developed with significant prognostic correlation with FL20 in a training set of RELEVANCE (n=264) patients, which was then validated in a different set of patients (n=116). These data indicate that FL tumors can be classified into MEM-like and GC-like subtypes that are biologically distinct and clinically different in risk profile. The FLCM assay can be used in routine clinical practice to identify MEM-like FL patients who might benefit from therapies other than R-chemo, such as the R2 combination. ClinicalTrials.gov identifier: RELEVANCE: NCT01476787 and NCT01650701 INTRODUCTION