Epcoritamab and Tazemetostat for the Treatment of Relapsed or Refractory Grade I-IIIa Follicular Lymphoma

Inclusion Criteria: * Documented informed consent of the participant and/or legally authorized representative * Assent, when appropriate, will be obtained per institutional guidelines * Agreement to allow the use of archival tissue from diagnostic tumor biopsies * If unavailable, exceptions may be granted with study principal investigator (PI) approval * Age: ≥ 18 years * Eastern Cooperative Oncology Group (ECOG) ≤ 2 * Histologically confirmed follicular lymphoma, grades 1-3A * Relapsed/ refractory disease after at least one line of prior lymphoma therapy * Radiologically measurable lymphadenopathy (≥ 1.5 cm) or ≥ 1 measurable extranodal lesion (long axis \> 1.0 cm) on CT scan or magnetic resonance imaging (MRI) * Fully recovered from the acute toxic effects (except alopecia) to ≤ grade 1 to prior anti-cancer therapy * WITHOUT BONE MARROW INVOLVEMENT: Absolute neutrophil count (ANC) ≥ 1,000/mm\^3 (NOTE: Growth factor use is allowed to reach ANC) * WITH BONE MARROW INVOLVEMENT: ANC ≥ 500/mm\^3 (NOTE: Growth factor use is allowed to reach ANC) * WITHOUT BONE MARROW INVOLVEMENT: Platelets ≥ 50,000/mm\^3 (NOTE: Platelet transfusions are within 14 days of platelet assessment if thrombocytopenia is secondary to disease involvement) * WITH BONE MARROW INVOLVEMENT: Platelets ≥ 25,000/mm\^3 (NOTE: Platelet transfusions are within 14 days of platelet assessment if thrombocytopenia is secondary to disease involvement) * Total bilirubin ≤ 2 x upper limit of normal (ULN) (unless ha…