Molecular profiling and disease tracking of posttransplant lymphoproliferative disorders using cell-free DNA

Posttransplant lymphoproliferative disorder (PTLD) is a life-threatening complication of hematopoietic stem cell or solid organ transplantation. Current prognostic tools for PTLD lack sufficient precision in predicting treatment response. This prospective feasibility study evaluates circulating tumor DNA (ctDNA) for risk stratification and treatment monitoring in PTLD. Plasma samples (n = 86) from 27 patients (13 positive for Epstein-Barr virus [EBV] positive and 14 EBV negative) were analyzed using targeted 115-gene sequencing and low-coverage whole-genome sequencing at diagnosis, after rituximab treatment and/or chemotherapy, and at end of treatment (EOT). At baseline, somatic single-nucleotide variants were detected in all patients. Multinucleotide variants were mostly detected in the B-cell lymphoma 6 superenhancer hypermutation region, especially in EBV-negative patients. Copy number variants were detected in 13 of 27 patients. An elevated ctDNA level at baseline indicated a poor outcome of rituximab monotherapy, and an undetectable ctDNA level at interim was correlated with better response. Seven patients showed completely undetectable ctDNA levels, whereas positron emission tomography-computed tomography (PET/CT) scan indicated active disease at interim; all 7 patients reached complete metabolic response by EOT. We demonstrate that ctDNA could potentially be used for prognostication and disease monitoring in PTLD, outperforming PET/CT in 8 patients. This indicates that ctDNA monitoring can complement PET/CT to guide early escalation to chemotherapy in high-risk patients, although larger cohorts are needed to validate these findings. This trial was registered at the Dutch Trial Register as NTR7402.