Background
The distinction of diffuse large B-cell lymphoma (DLBCL) into cell-of-origin (COO) subgroups (germinal center B-cell-like [GCB] or activated B-cell-like [ABC]) based on gene expression profiling is associated with prognosis and has potential therapeutic implications to mitigate the worse outcome for patients with DLBCL. Other phenotypic and molecular/cytogenetic features such as concurrent translocations of oncogene MYC and BCL2 and/or BCL6 (so-called double-/triple-hit lymphoma, DHL/THL) and coexpression of MYC and BCL2 proteins (so-called double-expressor lymphoma, DEL) are also recognized to have great prognostic impact (Swerdlow SH et al. Blood 2016;127(20):2375-2390). This study investigated the prevalence of COO, DHL/THL and DEL in a real-world cohort of patients with DLBCL who had documented results of diagnostic testing.
Methods
This study used the Flatiron Health electronic health record-derived de-identified database to abstract information on patients diagnosed with DLBCL between 2011-2019. Information on diagnostic testing from immunohistochemistry (IHC) for expression of MYC, BCL2, BCL6, CD10 or MUM1, and from fluorescence in situ hybridization (FISH) or karyotype analysis for rearrangement of MYC, BCL2 or BCL6 was abstracted from pathology reports or clinical visit notes, where available. We calculated the proportions of COO subgroups (GCB vs. ABC) that were derived from IHC testing results according to Hans algorithm (Hans C et al., Blood 2004;103(1):275-282), DHL/THL, and DEL. We also examined concordance of COO classification derived from IHC testing results with that directly reported by the healthcare providers. Differences in patient characteristics between IHC testing results-derived COO subgroups (GCB vs. ABC) were assessed using chi-square tests.
Results
4400 patients had documented results of IHC and 73% (n=3194) can be classified into either GCB or ABC DLBCL (GCB/ABC ratio of 1.38). 3205 patients had documented results of FISH or karyotype analysis and 8% (n=245) were DHL/THL; only 33 patients were DEL. Within the GCB DLBCL patients derived from IHC testing results (n=1854), 163 patients were DHL/THL and 11 were DEL, whereas 24 DHL/THL and 18 DEL were identified within the ABC type (n=1340). When comparing COO classification derived from IHC testing results (n=3194) with that directly reported by the healthcare providers (n=2765), additional 695 and 439 patients can be classified as GCB and ABC DLBCL by IHC, respectively (Table).
Univariate analysis showed that patients who were non-White ethnic group, diagnosed in academic centers, with lower body mass index but elevated serum lactate dehydrogenase levels and worse ECOG performance status, and without transformation from a prior indolent lymphoid malignancy, were more likely to be associated with ABC DLBCL (for all variables, p<0.05). There were no clinically meaningful and/or statistically significant differences in IHC testing results-derived COO classification (GCB vs. ABC) by age, gender, year of DLBCL diagnosis, geographic location of residency, type of insurance plan, tumor group stage, documentation of extranodal site or any other primary cancer history at the time of diagnosis.
Discussion
In this large real-world DLBCL cohort, a lower-than-expected proportion of DEL patients were identified vs. the 20-35% reported in the literature (Karube K and Campo E. Hematology 2015;52(2):97-106). This is likely due to our cohort of patients requiring clear evidence of coexpression for MYC and BCL2 (≥40% and >50%, respectively) that are not related to underlying chromosomal rearrangements, and few pathologists reported levels of percent staining for IHC testing among those with documented positive results of MYC/BCL2 protein coexpression. In addition, results from this study showed that only half of cases had COO classification documented by healthcare providers, despite available IHC results. Although this study indicated lack of details in the reporting of diagnostic testing (e.g. COO identification, levels of percent staining, methods for DLBCL subgroup identification), findings should be interpreted with caution, as patients with DLBCL might have been tested but not documented in the electronic health record system or might have biomarker testing performed at sites outside of the Flatiron Health network.
Disclosures
Yang: F. Hoffmann-La Roche: Current Employment. Zhang:F. Hoffmann-La Roche: Current Employment. Xiao:F. Hoffmann-La Roche: Current Employment. Hammer:Roche: Consultancy, Honoraria, Research Funding; Caris Lifesciences: Honoraria; PER Med education: Honoraria; PathEdEx: Current equity holder in private company. Prime:F. Hoffmann-La Roche: Current Employment.
High Ki67 proliferation index but not cell-of-origin subtypes is associated with shorter overall survival in diffuse large B-cell lymphoma
