Pemigatinib in Patients With Relapsed or Refractory B-cell Non-Hodgkin Lymphomas

The purpose of this clinical trial is to learn if the study drug pemigatinib is effective in treating patients with relapsed or refractory B-cell non-Hodgkin lymphomas.

Inclusion Criteria: * Subjects aged ≥ 18 years. * ECOG Performance Status ≤ 2. * Histologically confirmed MCL or MZL, including EMZL/MALT lymphoma, SMZL, and NMZL. --Patients with gastric MALT lymphoma and those who are H. Pylori positive need to have failed a trial of H. Pylori eradication and are either ineligible, have refused, or have failed gastric radiation therapy. * Have received at least two prior lines of systemic therapy and do not have FDA approved available therapies or have refused them. * Prior autologous hematopoietic cell transplantation (auto-HCT) and CAR-T cell therapy are eligible. * Patients with prior auto-HCT may be eligible if treatment completed after at least 3 months prior to first treatment * Patients with CAR T-cell therapy may be eligible if treatment completed after at least 1 month prior to first treatment * Subject must have an indication for systemic treatment. * Radiographically measurable disease by computed tomography (CT) scan, defined as at least one lesion \>1.5 cm in size or assessable disease in the opinion of the investigator. * Life expectancy \>3 months, in the opinion of the investigator. * Adequate organ function as defined as: * Hematologic: * Absolute neutrophil count (ANC) ≥ 1000/mm3 (≥1.0 x 10\^9/L) independent of G-CSF support (i.e., no G-CSF within the past 3 days), unless there is documented bone marrow involvement or splenomegaly with ensuing cytopenia in which case ANC of 750 cells/mm3 (0.75 x 10\^9/L) is permissible. Also, there should be no evidence of myelodysplasia or hypoplastic bone marrow. * Platelet count ≥ 75,000/mm3 (≥75 x 10\^9/L) independent of transfusion support (i.e., no transfusion within the past 3 days) unless there is documented bone marrow involvement in which case platelet count of 50,000 cells/mm3 (0.5 x 10\^9/L) is permissible. Patients must be responsive to transfusion support if given for thrombocytopenia and patients refractory to transfusion support are not eligible. Also, there should be no evidence of myelodysplasia or hypoplastic bone marrow. * Hemoglobin ≥ 8 g/dL independent of transfusion support (i.e., no transfusion within the past 3 days) unless there is documented bone marrow involvement or splenomegaly with ensuing cytopenia in which case hemoglobin of 7 g/dL is permissible. Patients must be responsive to transfusion support if given for anemia and patients refractory to transfusion support are not eligible. Also, there should be no evidence of myelodysplasia or hypoplastic bone marrow. * Hepatic: * Total Bilirubin ≤ 1.5x institutional upper limit of normal (ULN). or \