Testing the Effectiveness of the Anti-cancer Drug, Mirdametinib, in Treating Relapsed, Refractory Chronic Lymphocytic Leukemia

Inclusion Criteria: * Patients must have histologically or cytologically confirmed CLL or small lymphocytic lymphoma (SLL), as documented by a history at some point in time of an absolute peripheral blood B cell count \> 5000/mcL with a monoclonal B cell population coexpressing CD19, CD5, and CD23, or if CD23 negative, then documentation of the absence of t(11;14) or cyclin D1 overexpression. Alternatively, patients with lymphadenopathy in the absence of circulating disease will also be eligible for this study if lymph node biopsy or bone marrow biopsy has established the diagnosis of CLL with the above immunophenotype * Patients must have a current indication for treatment as defined by the iwCLL 2018 Guidelines (Hallek et al., 2018): * Massive or progressive splenomegaly; OR * Massive lymph nodes, nodal clusters, or progressive lymphadenopathy; OR * Grade 2 or 3 fatigue; OR * Fever ≥ 100.5°F or night sweats for greater than 2 weeks without documented infection; OR * Presence of weight loss ≥ 10% over the preceding 6 months; OR * Progressive lymphocytosis with an increase of ≥ 50% over a 2-month period or an anticipated doubling time of less than 6 months; OR * Evidence of progressive marrow failure as manifested by the development of or worsening of anemia and or thrombocytopenia * Patients must have measurable disease, defined as lymphocytosis \> 5,000/mcL, palpable or computed tomography (CT) measurable lymphadenopathy \> 1.5 cm, or bone marrow involvement…