T‑lymphoblastic lymphoma in a child diagnosed by metagenomic sequencing: A case report.

T-lymphoblastic lymphoma (T-LBL) is a rare subtype of non-Hodgkin's lymphoma with a higher incidence in children than adults. T-LBL often presents with multiple lymph node enlargements or mediastinal masses, which can cause local compression symptoms, and is frequently misdiagnosed as an infectious disease at an early stage. By summarizing a recently experienced case of T-LBL in a patient with a suspected infection, with an analysis of clinical features and diagnostic methods, the aim of the present study was to provide more information on the early diagnosis of tumors in patients suspected to have an infection. An 8-year-old boy presented at a local hospital with abdominal pain, chest tightness and shortness of breath for >5 days, and bilateral pleural, abdominal and pericardial effusion were considered. Following hospitalization without significant improvement under treatment with an anti-infection regimen and closed chest cavity drainage, the patient was transferred to another hospital. Once admitted, ultrasound examination indicated a large amount of pericardial and pleural effusion. Pericardiocentesis and closed chest cavity drainage were performed immediately. The initial pericardial drainage, which was bloody in appearance, gradually changed to a pale-yellow fluid. The patient continued to present with a temperature and remained under active anti-infection treatment. With repeated drainage procedures, it was observed that the volume of fluid obtained from the closed chest cavity exhibited an increasing trend. The cytological and tumor marker analysis of the idiopathic effusion specimens detected no abnormalities. Metagenomic next-generation sequencing (mNGS) of the pericardial drainage fluid was performed to identify the infectious pathogen. No pathogen was detected in the specimens, but the copy number variation (CNV) found in multiple chromosomes was highly suggestive of cancer development and progression. Lung imaging revealed no mediastinal lesions or tumors. The fluid from a subsequent closed chest drainage procedure was evaluated by mNGS for diagnostic purposes, and multiple CNVs were again noted, with similar results to those from the pericardial effusion. To determine the tumor type, immunophenotyping of the fluid was performed using flow cytometry and a diagnosis of T-LBL was confirmed. The patient was subsequently transferred to the hematology department for chemotherapy. The present case indicates that mNGS can not only differentiate between infections and tumors but also rapidly determine disease etiology.