• The patients diagnosed with follicular lymphoma with grade 1-3a, have received at least second-line systemic treatment, and at least one of the first-line treatments includes anti-CD20 monoclonal antibody (anti-CD20 monoclonal antibody monotherapy or combined chemotherapy). If the latest histopathological diagnosis is more than 6 months, a lymph node or tissue puncture or biopsy (resection or coarse needle puncture) must be performed.

• Age ≥18 years old, regardless of gender.

• The estimated survival time is more than 3 months.

• ECOG ≤ 2.

• Be able to follow the requirements of the research plan.

• The patients have at least one measurable lesion (any length of lymph node lesion \> 1.5cm or any length of extranodal lesion \> 1 cm) examined by computed tomography (CT)/ magnetic resonance imaging (MRI).

• Be able to understand and voluntarily provide informed consent.