Circulating Tumor DNA Profiling of a Diffuse Large B Cell Lymphoma Patient with Secondary Acute Myeloid Leukemia

SIMPLE SUMMARY: Liquid biopsy is a diagnostic procedure in which a blood sample taken from a cancer patient is searched for cell-free DNA that originates from tumor cells in the body. Analysis and quantification of this so-called circulating tumor DNA (ctDNA) can help to monitor therapy response and help to detect relapse earlier than routine clinical diagnostics. In this study, we report on a patient diagnosed with lymphoma who developed therapy-related acute leukemia and whom we profiled with liquid biopsy in blood samples taken at 13 time points over 26 weeks. Our liquid biopsy strategy used a combination of next-generation sequencing (NGS) and tumor-specific digital polymerase chain reaction (dPCR) assays. This strategy revealed not only lymphoma mutation dynamics during treatment, but was also able to capture the onset of therapy-related acute leukemia by detecting two leukemia specific mutations. We conclude that liquid biopsy based on analyzing ctDNA by combining targeted NGS with mutation-specific dPCR is a feasible tool for monitoring treatment response in lymphoma patients and is also capable of detecting therapy-related acute leukemia. ABSTRACT: Diffuse large B cell lymphomas (DLBCL) are the most common neoplasia of the lymphatic system. Circulating cell-free DNA released from tumor cells (ctDNA) has been studied in many tumor entities and successfully used to monitor treatment and follow up. Studies of ctDNA in DLBCL so far have mainly focused on tracking mutations in peripheral blood initially detected by next-generation sequencing (NGS) of tumor tissue from one lymphoma manifestation site. This approach, however, cannot capture the mutational heterogeneity of different tumor sites in its entirety. In this case report, we present repetitive targeted next-generation sequencing combined with digital PCR out of peripheral blood of a patient with DLBCL relapse. By combining both detection methods, we were able to detect a new dominant clone of ctDNA correlating with the development of secondary therapy-related acute myeloid leukemia (t-AML) during the course of observation. Conclusively, our case report reinforces the diagnostic importance of ctDNA in DLBCL as well as the importance of repeated ctDNA sequencing combined with focused digital PCR assays to display the dynamic mutational landscape during the clinical course.