Mutations in the Phosphoinositide 3-Kinase Pathway (PI3K) Are Associated with Poor Overall Survival (OS) in Patients with Diffuse Large B-Cell Lymphoma Treated with R-CHOP

Introduction:

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disease that is characterized by recurrent translocations and somatic mutations. Prognosis has been associated with clinical presentation, cell-of-origin, and genetic aberrations. The aim of this study was to determine whether somatic mutations are associated with OS in patients with DLBCL who have been treated with R-CHOP therapy (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone).

Methods:

We identified 354 patients between 2000-2016 at City of Hope and University of Manitoba with a diagnosis of de novo DLBCL who were treated with R-CHOP therapy. Patients with primary mediastinal large B-cell lymphoma, primary CNS B-cell lymphoma, and those with HIV or immunodeficiency were excluded. A custom targeted panel with 334 genes which included the most frequently mutated genes in B-cell lymphoma was used. Library prep with paired end 100 bp sequencing and 6-10 million reads/case was performed on an Illumina HiSeq 2500. Cases were evaluated by immunohistochemistry (IHC) for cell-of-origin by the Hans algorithm, as well as MYC (>40%) and BCL-2 (>50%) protein overexpression. Fluorescence in situ hybridization analysis also was performed using BCL2/IGH, BCL6/IGH, and MYC probes. Pathway analysis was performed using Gene Ontology and Ingenuity Pathway Analysis (IPA). Overall survival estimates for 5-year survival were estimated using Kaplan Meier methods. Both univariate and multivariable hazard ratios were calculated by Cox regression with two-sided p-values presented. The final multivariable model includes significant terms controlling for patient International Prognostic Index (IPI) score.

Results:

To date, 215 patients (median age 59 years, Male:Female ratio of 1.44:1) had complete clinical information and tissue available for sequencing. Between the two centers, there were no significant differences in patient demographics, International Prognostic Index (IPI) score, or clinical recurrence status. Germinal center B-cell origin (GCB) type DLBCL was more common (57%) compared to non-GCB type (43%). The most frequently mutated genes were KMT2D (29%), CREBBP (20%), TP53 (20%), TET2 (16%), B2M (14%), and MYD88 (13%), as well as 14 other genes (>10% each). There were 24 (11%) double- or triple-hit lymphomas (MYC, BCL2, and or BCL6) and 35 (16%) double-protein expressors (MYC and BCL2). Mutations in the phosphoinositide 3-kinase/Akt/mTOR pathway (5%, NF1, PIK3CD) (5-yr OS 50% vs 74%, HR = 6.3, p=0.0009), B-cell differentiation genes (13%, BCL6, PRDM1) (5-yr OS 47% vs 77%, HR = 3.1, p=0.0015), ubiquitination pathway (7%, KLHL14, UBR5) (5-yr OS 48% vs 75%, HR = 2.5, p=0.018), and histone and histone modifier genes (31%, HIST1H2BC, KMT2D) (5-yr OS 58% vs 79%, HR = 2.1, p=0.012) were associated with poor OS in DLBCL, independent of IPI score.

Conclusion:

Targeted sequencing is effective for identifying known mutations associated with the pathogenesis of DLBCL. In this study, mutations involving the PI3K/Akt/mTOR pathway were associated with the worst outcome in patients treated with R-CHOP therapy. Identifying mutations in major pathways may help with prognostication in this heterogenous disease, and provide information useful for targeted therapy.