Clonal heterogeneity and level of ctDNA for IG-V(D)J as potential prognostic markers in FL?

This month in the Oncotarget journal, Clémentine Sarkozy from Hospices Civils de Lyon, Centre Hospitalier Lyon-Sud, Service d’Hématologie, France, and colleagues published the results of a study which aimed to quantify the heterogeneity of circulating tumor DNA (ctDNA) that encodes IG-V(D)J and assess its suitability at diagnosis as a potential prognostic marker in patients with FL. IG-V(D)J is a mutated clonal receptor gene which has been identified in FL patients. The authors assessed the clonal heterogeneity of ctDNA for IG-V(D)J using Next-Generation Sequencing (NGS) of both tumor cells and blood plasma from 34 patients who participated in the PRIMA trial who had plasma data.

Highlights:

• Tumor clonotype detected in 85% (29/34) FL Pts tumor samples and in 74% (25/34) plasma samples
• Heterogeneity as a prognostic marker:
  • Seventy-five percent of pts with IGH-V or -D tumor clonotype had detectable subclones in the tumor or plasma
  • Eighteen pts had several different subclones that were detectable at diagnosis in tumor and/or plasma
  • Subclonal composition differed between tumor and plasma samples in over half of patients
  • Of those with multiple subclones, the median number of subclones in tumor samples was 9
  • Trend seen to fewer subclones indicating poorer PFS (P=0.12)
    • Nine or more subclones in 6/15 pts; these pts had a 6-year PFS of 83%
    • Less than 9 subclones in 9/15 pts; these pts had a 6-year PFS of 44%

• ctDNA level as a prognostic marker:
  • Median ctDNA level was used as a threshold to define ‘high’ or ‘low’ ctDNA level
  • High group had significantly lower mPFS (15.3 months vs not reached, P=0.004)
  • From ctDNA level, FLIPI score, circulating lymphoma cell presence, and bone marrow involvement, only high level of ctDNA was found to be predictive of PFS (HR 6.2, P=0.001)

In conclusion, the authors state that NGS could be more sensitive than qPCR methods and has revealed “the marked clonal heterogeneity of follicular lymphoma”. Furthermore, the ctDNA level of the most frequent clone at diagnosis had prognostic value and was predictive of PFS. Although preliminary, the data in this study has demonstrated the potential clinical and prognostic value of using NGS in FL patients.

Abstract:

Recent advances in next-generation sequencing (NGS) have enabled the quantitation of circulating tumour DNA (ctDNA) encoding the clonal rearranged V(D)J immunoglobulin locus. We aimed to evaluate the clonal heterogeneity of follicular lymphoma (FL) in the tumour and the plasma at diagnosis and to assess the prognostic value of the ctDNA level. Plasma samples at diagnosis were available for 34 patients registered in the PRIMA trial (NCT00140582). One tumour clonotype or more could be detected for 29 (85%) and 25 (74%) patients, respectively, in the tumour or plasma samples. In 18 patients, several subclones were detected in the tumour (2 to 71 subclones/cases) and/or in the plasma (2 to 20 subclones/cases). In more than half of the cases, the distribution of subclones differed between the tumour and plasma samples, reflecting high clonal heterogeneity and diversity in lymphoma subclone dissemination. In multivariate analysis, a high level of ctDNA was the only independent factor associated with patients' progression-free survival (HR 4, IC 95 (1.1-37), p=.039). In conclusion, an NGS-based immunosequencing method reveals the marked clonal heterogeneity of follicular lymphoma in patients with FL, and quantification of ctDNA at diagnosis represents a potential powerful prognostic biomarker that needs to be investigated in larger cohorts.