Abstract 779: Clonal B-cell expansion and the potential challenges to blood-based early cancer detection
Authors: Xiang Jing , Liu Qinwen , Shaknovich Rita , Venn Oliver 
Published: April 2023

Abstract
Introduction: Confounding signals originating from white blood cells (WBCs) have been reported as a potential source of false positives for blood-based early cancer detection and disease monitoring. Additionally, the level of aberrant signal originating from clonal expansion (CE) in precursor conditions, such as monoclonal B-cell lymphocytosis (MBL) and monoclonal gammopathy of undetermined significance (MGUS), is not well understood. To characterize CE in a potential screening population, we profiled samples from non-cancer (NC) participants and compared them to samples from participants with hematological precursor and neoplastic conditions (HPNCs).
Methods: Using LymphoTrack IGH FR1 Assay (Invivoscribe, Inc), we sequenced DNA derived from WBCs from a subset of enrollees in the Circulating Cancer Genome Atlas study (NCT02889978) comprising NC participants, balanced for age and gender, and participants diagnosed with an HPNC (chronic lymphocytic leukemia [CLL], multiple myeloma [MM], MBL, or MGUS). Additional samples were titrated and processed to determine the limit of quantification (LoQ).
Results: Using 12 titration samples, we determined the LoQ of detecting an unknown clone against a polyclonal background to be 0.1% of the total reads. The threshold used to determine evidence of CE was 2.5% of the total reads.
We sequenced samples from 112 individuals, 67 of whom were NC participants (35 male of median [range] age 67 [33-85] years; 32 female of 60 [30-85] years). A large fraction of NC samples (10/67; 15%) showed evidence of CE: 9/10 (90%) were monoclonal with clonal percent total reads (PTR) ranging from 2.7% to 80.4% (median: 6.0%), and 7/9 had a mutation rate &gt;2%, indicating somatic hypermutation (SHM). One sample exhibited oligoclonality with 2 clones (6.6% and 3.2%), and both had SHM. Most NC samples (57/67; 85%) lacked evidence of CE: median top clone PTR of 0.10% (mean: 0.18%; SD: 0.24%) and median Simpson clonality of 0.0021 (mean: 0.0030; SD: 0.0030). A positive correlation between the top clone PTR and age was also observed (⍴=0.41 all participants, ⍴=0.43 excluding 80.4% PTR).
All CLL samples (9/11 monoclonal; 2/11 oligoclonal) and 3/4 MBL samples showed evidence of CE. Consistent with the observation that a limited number of plasma cells are expected to be in circulation, only 3/10 MM samples and 7/20 MGUS samples showed evidence of CE; 1 MM and 3 MGUS samples had a top clone PTR of &gt;40%.
Conclusion: A large fraction of NC samples (15%) had evidence of expanded lymphoid clones with SHM. The PTR of the top clone underscores the higher frequency of CE associated with increased age in asymptomatic participants. Clonal expansion of blood cell lineages can also carry genetic or epigenetic alterations that are similar to those associated with non-hematologic cancers. Thus, differentiating aberrant signals originating from various hematologic compartments is key for accurate early cancer detection.
Citation Format: Jing Xiang, Qinwen Liu, Rita Shaknovich, Oliver Venn. Clonal B-cell expansion and the potential challenges to blood-based early cancer detection [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 779.