Inclusion Criteria:  Children with mature B-cell lymphoma (BL, DLBCL, high-grade B-cell lymphoma, mediastinal large B-cell lymphoma) that met the criteria and required treatment upon histological and pathological diagnosis; Age: < 18 years old; The working status of the Eastern Cooperative Oncology Group (ECOG) (PS) : 0-2 points; CT/MRI measurable lesion was defined as the longest diameter of at least 1 lymph node ≥ 1.5cm, and it was clearly measurable in 2 vertical directions; Complete clinical laboratory examination and pathological examination information; Patients can be evaluated on time, and the required samples can be obtained throughout the testing process; After the patient is informed of the project, the informed consent signed by the patient or his legal representative is obtained.  Exclusion Criteria:  Patients with any of the following items will not be enrolled in this study:  Incomplete baseline samples (preoperative plasma samples, tissue, bone marrow, cerebrospinal fluid) due to various reasons; The follow-up samples cannot be obtained during the monitoring process; The researcher considered it unsuitable for enrollment.