A Drop of Blood to Lead the Way.

In patients with Epstein-Barr virus-driven hemophagocytic lymphohistiocytosis (EBV-HLH), identifying the underlying cause poses a significant diagnostic challenge. HLH may precede overt disease, and early directed treatment for HLH can obscure histopathological findings. A liquid biopsy enables the detection of tumor-derived DNA from various sources, including cell-free DNA, circulating tumor cells, extracellular vesicles, and tumor-educated platelets, and might aid in this setting. This case presents a young patient with EBV-HLH, in which genomic analysis of tumor-derived DNA from circulating tumor cells led to the diagnosis of an EBV-positive NK/T-cell lymphoma-where conventional tissue biopsies had failed. This report underscores the potential of the liquid biopsy as a valuable diagnostic tool in complex cases of EBV-HLH.