APPLICATION OF CELL‐OF‐ORIGIN SUBTYPES DETERMINED BY DIGITAL GENE EXPRESSION IN HIV ‐RELATED DIFFUSE LARGE B ‐CELL LYMPHOMAS

Abstract

Background: Diffuse large B cell lymphoma (DLBCL) can be divided according to cell of origin (COO) in germinal center B-cell-like (GCB) and activated Bcell- like (ABC) that have been shown different prognosis. Immunohistochemistry (IHC)-based algorithms and recently, Lymph2Cx assay, a digital test based on the expression of 20 genes, have been developed to facilitate COO assignment in clinical practice. Although the importance of COO is well established in DLBCL arising in immunocompetent individuals, its applicability on HIVinfected patients has been scarcely studied. Aims: To study the characteristics and prognostic impact of COO subtypes in a series of HIV-related DLBCL using the Lymph2Cx assay and to compare the results with those obtained with an IHC-based algorithm. Methods: A series of 55 patients with the diagnosis of HIV-related DLBCL (N=48), high-grade B-cell lymphoma (HGBL) with MYC and BCL2 and/or BCL6 rearrangements (N=3), or HGBL NOS (N=4) was studied. The following clinical parameters were collected from records: age, gender, ECOG, extranodal and bulky disease, B-symptoms, Ann-Arbor stage, LDH and beta2-microglobulin, HCV and HBV serology, history of opportunistic infection and of AIDS-defining illness, onset of combination antiretroviral therapy, CD4-counts and HIV loads. IHC and FISH studies were performed on tissue microarrays. RNA was extracted from FFPE samples with RecoverAll kit (Ambion, Carlsbad, California) and digital GEP was determined with the Lymph2Cx assay (NanoString Technologies, Seattle, WA). Cohen's kappa was calculated to measure the agreement between COO given by Hans algorithm and Lymph2Cx assay. (Table presented). Results: The median follow-up of living patients was 8.5 years. IHC studies showed that 35.8% of the cases expressed CD10, 61.5% expressed BCL6, 55.8% expressed MUM1, and according to Hans algorithm 56.6% had a non- GC phenotype. CD30 was expressed in 15.4% of the cases and EBER was found in 21.2%. The expression of MYC was detected in 32.7% of the cases and BCL2 in 44%, and 18% were dual expressers. Rearrangements involving MYC, BCL2 and BCL6 were detected in 26%, 8% and 28%, respectively. The Lymph2Cx assay assigned a COO to all 55 studied cases, 63.6% were GCB subtype, 20% were ABC subtype, and 16.4% were unclassified. The only clinical feature significantly associated with a defined COO subtype was B-symptoms (ABC=81.8% vs GCB=28.6%, P=0.003) and HIV-load tended to be more frequently observed in ABC (90%) than in GCB (58.1%, P=0.066). Regarding IHC and FISH results, MYC rearrangements were only detected in GCB cases and expression of CD10 and BCL6 tended to be associated with GCB (Table 1). Hans algorithm and Lymph2Cx assay differently assigned COO subtypes (?=-0.288, P=0.029) showing that 44.1% of the GCB cases had a non-GC phenotype according to Hans. Only patients treated with RCHOP were considered in survival analyses (N=47). COO subtypes had neither impact on OS nor PFS, independently of being determined with Hans or Lymph2Cx assay. Features associated with shorter OS and PFS were history of AIDS-defining illnesses, HCV-infection and dual MYC and BCL2 expression. Extranodal disease and increased MYC or BCL2 expression were also bad prognostic factors for PFS. Summary/Conclusions: In HIV-related lymphomas, COO subtypes were discordantly assigned with Hans and Lymph2Cx assay and COO subtypes showed no impact on outcomes, independently of the method applied.