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Letters to the Editor
ly additional CNS-specific processes not captured through transcriptome profiling.
Herein, we present a comprehensive description of clonal evolution, gene mutations and gene expression changes associated with CNS and systemic relapse in DLBCL. Our analysis of clonal evolution patterns under- lying CNS relapse revealed clear clonal divergence. In general, mutations specifically associated with the relapsing clone were not found at measurable levels in preceding diagnostic specimens. Our cohort for exome sequencing of paired samples was limited due to inher- ent challenges associated with collecting biospecimens of this nature, as a limited number of patients undergo sampling of brain parenchyma at the time of relapse. Further, a divergent mode of clonal evolution is not unique to CNS relapse, but rather a general property of cancers that harbor underlying intra-tumoral hetero- geneity. Divergent evolution has also been demonstrated in DLBCL,10,11 although – to the best of our knowledge – no prior study has applied state-of-the-art phylogenetic reconstruction tools to trace clonal trajectories in the specific context of CNS relapse. The phylogenetic por- traits that we could draw exert a cautionary tale, illus- trating that efforts to improve patient outcomes will need to take into consideration the molecular landscape at the time of lymphoma relapse. Moreover, well-known challenges to predict CNS relapse may be explained by both inter-patient and intra-tumor heterogeneity that is universally recognized in DLBCL.
Alterations of ABC subtype-associated genes are fre- quently seen in primary CNS lymphoma,12 which is often of an ABC phenotype,13 and are also characteristic of the recently identified C5/MCD subtype of DLBCL that is associated with extranodal involvement and poor outcome.14,15 In the gene mutation analysis, the strongest enrichment was seen for MYD88, although this gene was almost as often mutated in cases with subsequent systemic relapse. Conversely, we found that several gene mutations that were more commonly seen in patients experiencing systemic, as opposed to CNS relapse (e.g., TP53). Other mutations such as KTM2D, characteristic of the C3/EZB subtype of DLBCL, appeared to be com- paratively infrequent in CNS relapse cases, perhaps sug- gesting that the KTM2D-mutant phenotype is not con- ducive to establishing tumors in the CNS. Lastly, we found that biological pathways were differentially enriched between clinical risk groups in the ABC versus GCB subtype of DLBCL. Signals underlying CNS relapse were overall weaker compared with signals underlying systemic relapse, potentially reflective of clonal diver- gence and resulting phenotypic shifts that may accompa- ny CNS relapse. It seems unlikely that a gene expres- sion-based biomarker can be developed to positively identify patients at highest risk of CNS relapse, beyond the information that is already contained within the transcriptional footprints that define known DLBCL sub- types. In contrast, large-scale, integrative analyses and in-depth characterization of clonal trajectories hold the promise to increase our ability to understand dissemina- tion of DLBCL into the CNS.
Keren Isaev,1 Daisuke Ennishi,2 Laura Hilton,3
Brian Skinnider,2 Karen L. Mungall,4 Andrew J. Mungall,4 Mehran Bakthiari,1 Rosemarie Tremblay-LeMay,5
Anjali Silva,1 Susana Ben-Neriah,2 Merrill Boyle,2
Diego Villa,2 Marco A. Marra,4 Christian Steidl,2
Randy D. Gascoyne,2 Ryan D. Morin,3 Kerry J. Savage,2 David W. Scott2# and Robert Kridel1#
1Princess Margaret Cancer Center - University Health Network,
Toronto, Ontario; 2Center for Lymphoid Cancer, Britsh Columbia Cancer, Vancouver, British Columbia; 3Simon Fraser University, Burnaby, British Columbia; 4Canada’s Michael Smith Genome Sciences Center, British Columbia Cancer, Vancouver, British Columbia and 5Laboratory Medicine Program - University Health Network, Toronto, Ontario, Canada.
#DWS and RK contributed equally as co-senior authors. Correspondence:
ROBERT KRIDEL - robert.kridel@uhn.ca doi:10.3324/haematol.2020.255950
Received: April 22, 2020.
Accepted: August 6, 2020.
Pre-published: August 13, 2020. Disclosures: no conflicts of interest to disclose.
Contributions: RK and DWS designed the study, collected data, analyzed data and wrote the manuscript; KI analyzed data and wrote the manuscript. DE, BS, MB, RTL, BM, SBN, and MB reviewed samples, extracted and inventoried samples and/or pro- vided data; LH and RM provided bioinformatic guidance; KM, AJM and MAM provided critical support for exome sequencing and analysis; DV, CS, RDG and KJS provided samples and clini- cal data; AS reviewed and corrected bioinformatic scripts related to this manuscript; all authors approved the final version of the manu- script.
Acknowledgments: we thank the expert staff of the Michael Smith’s Genome Sciences Center at Britsh Columbia Cancer Center in Vancouver and The Center for Applied Genomics at SickKids in Toronto for generating exome sequencing data and gene expression. We thank Dr. Osvaldo
Espin-Garcia for expert statistical advice.
Funding: this work was supported by an Innovation Grant (award # 703505) from the Canadian Cancer Society Research Institute (DWS), by a Genome Canada Large-Scale Applied Research Project (Genome Canada #13124, Genome BC #271LYM, Canadian Institutes of Health Research #GP1-155873 and the BC Cancer Foundation) (CS, DWS, MAM), the Ontario Research Fund (RK), and by the Princess Margaret Cancer Foundation (RK).
References
1. Kridel R, Dietrich P-Y. Prevention of CNS relapse in diffuse large B-cell lymphoma. Lancet Oncol. 2011;12(13):1258-1266.
2. Boehme V, Schmitz N, Zeynalova S, Loeffler M, Pfreundschuh M. CNS events in elderly patients with aggressive lymphoma treated with modern chemotherapy (CHOP-14) with or without ritux- imab: an analysis of patients treated in the RICOVER-60 trial of the German High-Grade Non-Hodgkin Lymphoma Study Group (DSHNHL). Blood. 2009;113(17):3896-3902.
3. Schmitz N, Zeynalova S, Nickelsen M, et al. CNS International Prognostic Index: a risk model for CNS relapse in patients with diffuse large B-cell lymphoma treated with R-CHOP. J Clin Oncol. 2016;34(26):3150-3156.
4. Boehme V, Zeynalova S, Kloess M, et al. Incidence and risk factors of central nervous system recurrence in aggressive lymphoma--a survey of 1693 patients treated in protocols of the German High- Grade Non-Hodgkin’s Lymphoma Study Group (DSHNHL). Ann Oncol. 2007;18(1):149-157.
5. El-Galaly TC, Villa D, Michaelsen TY, et al. The number of extra- nodal sites assessed by PET/CT scan is a powerful predictor of CNS relapse for patients with diffuse large B-cell lymphoma: an international multicenter study of 1532 patients treated with chemoimmunotherapy. Eur J Cancer. 2017;75:195-203.
6. Savage KJ, Slack GW, Mottok A, et al. Impact of dual expression of MYC and BCL2 by immunohistochemistry on the risk of CNS relapse in DLBCL. Blood. 2016;127(18):2182-2188.
7. Klanova M, Sehn LH, Bence-Bruckler I, et al. Integration of cell of origin into the clinical CNS International Prognostic Index improves CNS relapse prediction in DLBCL. Blood. 2019;133(9): 919-926.
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