Early Detection of Post-Transplant Lymphoproliferative Disorder Using Circulating Tumor DNA

Purpose Diffuse large B cell (DLBCL)-like post-transplant lymphoproliferative disorder (PTLD) affects up to 10% of thoracic transplant recipients. Although 50% of PTLDs can be related to Epstein-Barr virus (EBV) infection, and high or increasing EBV viral load may precede EBV+ PTLD, preemptive monitoring of EBV titers does not reliably predict PTLD . Consequently, we assessed the utility of circulating tumor DNA (ctDNA), a promising biomarker for many cancers including DLBCL, for early detection of PTLD. Methods We used Cancer Personalized Profiling by Deep Sequencing (CAPP-Seq) to analyze diagnostic tumor and plasma samples and matched germline DNA in a cohort of 10 heart and lung transplant recipients who developed PTLD to identify somatic alterations. We compared mutational patterns in PTLD to 173 de novo DLBCL cases. We additionally sequenced serial post-transplant plasma samples preceding diagnosis in 5 patients (2 EBV-, 3 EBV+), and during or after treatment in 8 patients, to determine the dynamics of ctDNA and compared these patterns to clinical outcomes and EBV titers. Results There was no significant difference in mutational burden between patients with PTLD and de novo DLBCL (median PTLD variants: 216, IQR = 79 - 321; median de novo DLBCL variants: 143.5, IQR = 45 - 243.8; p = 0.35), although there was a trend toward greater variant count in EBV- compared to EBV+ PTLD (p = 0.064). The prevalence of alterations in known driver genes was similar between PTLD and de novo DLBCL. Prediagnostic plasma samples were available for 5 cases, and we detected ctDNA in all patients prior to clinical diagnosis (mean lead time = 114 days, maximum lead time 1.5 years). Levels of ctDNA during and after treatment were concordant with EBV titers in EBV+ disease and with clinical response in all patients. Conclusion PTLD patients have detectable ctDNA prior to clinical diagnosis. Development of screening tools utilizing both ctDNA and EBV titers would facilitate early detection of PTLD in the transplant population.