Liquid biopsy provides complementary information to tissue biopsies for molecular classification of DLBCL patients

Diffuse large B-cell lymphoma is a molecular heterogeneous disease with a variable clinical course and prognosis. Recent studies have identified different molecular clusters on tissue biopsy. Liquid biopsy is a non-invasive tool that allows the collection of circulating tumor DNA (ctDNA) shed by apoptotic tumor cells potentially deriving from all the different sites of the lymphoma. This may provide an integrative source of tumor DNA for DLBCL genotyping. The aims of the study are: i) to identify new prognostic molecular markers on ctDNA and on lymph node biopsy (LN); and ii) to compare the DLBCL molecular clusters between the LN and the ctDNA. The mutational profiling performed in 77 DLBCL patients, through a NGS approach, allows to identify at least one somatic non-synonymous mutation in 92.2% of patients in the LN biopsy, and in 87.0% in the ctDNA. Mutation analysis of different compartments allowed to identify mutations with potential clinical impact: GRHPR (p=0.035) and SGK1 (p=0.039) mutations in ctDNA, and MYC mutations in LN (p=0.021) were associated with a shorter PFS. Moreover, ctDNA levels harbor prognostic impact since higher levels of ctDNA (22.5 log hGE/mL) showed a significantly worse PFS (p=0.025) and OS (p=0.004). Based on the mutations identified, the LymphGen tool allowed to assign to a specific molecular cluster 46.5% of patients on the LN biopsy, and 40.3% on the liquid biopsy. The combination of mutational data from LN and ctDNA improved DLBCL assignment to a specific cluster, thus classifying 48.7% of cases. From a clinical perspective, patients belonging to the BN2 and ST2 clusters showed a favorable outcome with a 36-month PFS of 100% compared to 62.3% for patients belonging to the MCD or EZB clusters (p=0.040). The combination of mutational data from LN and ctDNA provides complementary information for the molecular classification and prognostic stratification of newly diagnosed DLBCL patients.