This study is a prospective cohort study. The case group will include patients with primary central nervous system lymphoma confirmed by imaging and pathology. The control group will include patients with pathologically confirmed diffuse large B-cell lymphoma who have been excluded from central nervous system involvement, as well as age- and gender-matched healthy volunteers (hematopoietic stem cell donors). Baseline data (as described below) will be collected. Patients with primary CNS lymphoma will undergo follow-up every 3 months, with immediate follow-up if clinical symptoms arise.

Inclusion Criteria:

1. Aged between 18 and 75 years.
2. The case group must have a confirmed diagnosis of primary central nervous system lymphoma (PCNSL) and must not have received any antitumor therapy prior to baseline sample collection.
3. Must sign an informed consent form, agree to participate in this study, and provide samples and clinical information as required.
4. Case group patients must have complete supporting imaging and pathology data.

Exclusion Criteria:

1. Presence of other systemic malignancies.
2. Presence of severe infections or metabolic disorders.
3. Use of antimetabolites or chemotherapy drugs within one week prior to sample collection.
4. Pregnant or lactating women.
5. Concurrent severe internal medical conditions (e.g., end-stage renal disease, heart failure, liver failure).
6. Patients unable to complete study requirements due to psychiatric disorders or cognitive impairment.

Hematopoietic stem cell donor

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