Selinexor Plus Combination Chemotherapy in Treating Patients With Advanced B Cell Non-Hodgkin Lymphoma

Inclusion Criteria: * Phase 1 Part: Patients with pathologically confirmed advanced stage B-cell NHL (Ann Arbor stage 3 or 4) for whom R-CHOP is considered appropriate therapy; newly diagnosed DLBCL, newly diagnosed low grade B cell NHL, and previously treated low grade B cell NHL patients in first relapse after a prior treatment with non-anthracycline containing chemotherapy are allowed; double hit and transformed diffuse large B cell lymphoma are allowed \* Allowed low grade B cell lymphomas will include follicular lymphoma any grade, marginal zone lymphoma including mucosa-associated lymphoid tissue (MALT) lymphoma, indolent mantle cell lymphoma and Waldenstrom's macroglobulinemia * Phase 2 Part: Patients with pathologically confirmed newly diagnosed diffuse large B cell lymphoma (Ann Arbor stage 3 or 4); newly diagnosed double hit and transformed diffuse large B cell lymphoma are allowed * Patients must have measurable disease, defined as at least one lesion above and below the diaphragm or stage 4 disease that can be accurately measured in at least one dimension; lymph nodes should be considered abnormal if the long axis is \> 1.5 cm, regardless of the short axis * Allowed prior therapy: * Newly diagnosed DLBCL and low grade B cell lymphoma: No prior therapy is allowed except steroids equivalent to maximum of prednisone 20 mg once daily for maximum of seven days prior to registration * Relapsed/refractory low grade B cell lymphoma (only allowed in phase I): A mi…