Inclusion Criteria:

          -  Male or female subject aged ≥ 18 years.

          -  Newly diagnosed or hypomethylating agent (HMA) refractory chronic myelomonocytic
             leukemia (CMML -0/-1/-2; 2016 WHO classification) with RAS pathway activation as
             determined by standard of care hematopoietic cell sequencing results on peripheral
             blood or bone marrow demonstrating NRAS, KRAS, PTPN11, FLT3, CBL, JAK2, BRAF or NF1
             mutations at variant allele frequency ≥ 5%.

          -  ECOG Performance Status ≤ 3.

          -  Adequate organ function as defined as:

               -  Hepatic:

                    -  Total Bilirubin ≤ 1.5x institutional upper limit of normal (ULN)

                    -  Unless elevation is related to Gilbert's syndrome, hemolysis, or thought to
                       be due to leukemic hepatic involvement.

                    -  AST(SGOT)/ALT(SGPT) ≤ 3 × institutional ULN ----Unless elevation is related
                       to leukemic hepatic involvement.

               -  Renal:

                  ---Serum creatinine ≤ 2x ULN

               -  OR

                    -  Estimated creatinine clearance ≥ 30 mL/min by Cockcroft-Gault formula:

                    -  Males: ((140-age)×weight[kg])/(serum creatinine [mg/dL]×72)

                    -  Females: (((140-age)×weight[kg])/(serum creatinine [mg/dL]×72))×0.85

          -  Left ventricular function ≥ 50% as assessed by echocardiogram.

          -  Negative pregnancy test for women of childbearing potential or evidence of
             post-menopausal status. Women will be considered post-menopausal if they have been
             amenorrheic for 12 months without an alternative medical cause. The following
             age-specific requirements apply:

               -  Women <50 years of age would be considered post-menopausal if they have been
                  amenorrheic for 12 months or more following cessation of exogenous hormonal
                  treatments and if they have luteinizing hormone and follicle-stimulating hormone
                  levels in the post-menopausal range for the institution or underwent surgical
                  sterilization (bilateral oophorectomy or hysterectomy).

               -  Women ≥50 years of age would be considered post-menopausal if they have been
                  amenorrheic for 12 months or more following cessation of all exogenous hormonal
                  treatments, had radiation-induced menopause with last menses >1 year ago, had
                  chemotherapy-induced menopause with last menses >1 year ago, or underwent
                  surgical sterilization (bilateral oophorectomy, bilateral salpingectomy or
                  hysterectomy).

          -  Highly effective contraception for both male and female subjects throughout the study
             and at least 2 weeks month after the last dose of study therapy as described in
             Section 7.4 of the protocol.

          -  Recovery to baseline or Grade ≤ 1 CTCAE v5.0 from toxicities related to any prior
             treatments, unless AE(s) are clinically nonsignificant and/or stable on supportive
             therapy.

          -  Able to provide informed consent and willing to sign an approved consent form that
             conforms to federal and institutional guidelines.

        Exclusion Criteria:

          -  Previous exposure to experimental MEK inhibitors for CMML.

          -  Grade 2 or greater QTc prolongation on screening electrocardiogram (ECG) or clinically
             significant cardiovascular disease (uncontrolled or symptomatic atrial arrhythmias,
             congestive heart failure, myocardial infarction/CABG/PCI within 6 months of screening,
             uncontrolled arterial hypertension or history of ventricular arrhythmia)

          -  Clinical or laboratory evidence of central nervous system (CNS) leukemia.

          -  Major surgery within 4 weeks prior to study drug initiation.

          -  History of interstitial lung disease.

          -  History of retinal detachment, central serous retinopathy (CSR), retinal vein
             occlusion (RVO), or at risk for CSR or RVO following screening ophthalmologic exam.

          -  Patients with muscular and/or neuromuscular disorders associated with elevated CPK
             (e.g. inflammatory myopathies, muscular dystrophy, amyotrophic lateral sclerosis, or
             spinal muscular atrophy).

          -  Any active significant gastrointestinal dysfunction interfering with the patient's
             ability to swallow or absorb the study treatment.

          -  Pregnant or nursing (lactating) women.

          -  On chronic treatment with strong CYP3A inhibitors or patients taking St. John's Wort,
             carbamazepine, efavirenz, phenytoin, rifampin, and other strong and moderate CYP3A
             inducers.

          -  Diagnosis of any other malignancy within 2 years before study enrollment, except for
             adequately treated basal cell or squamous cell skin cancer, carcinoma in situ of the
             breast, bladder or cervix, low-grade (Gleason 6 or below) prostate cancer on
             surveillance with no plans for treatment intervention (eg, surgery, radiation, or
             castration), or prostate cancer that has been adequately treated with prostatectomy or
             radiotherapy and currently with no evidence of disease or symptoms.

          -  Known HIV infection with a detectable viral load at the time of screening.

             --Note: Patients on effective antiretroviral therapy with an undetectable viral load
             at the time of screening are eligible for this trial.

          -  Active infection including tuberculosis (clinical evaluation that includes clinical
             history, physical examination, and radiographic findings, and TB testing in line with
             local practice), hepatitis B (known positive HBV surface antigen (HBsAg) result), or
             hepatitis C.

             --Note: Patients with a past or resolved HBV infection (defined as the presence of
             hepatitis B core antibody [anti-HBc] and absence of HBsAg) are eligible. Patients
             positive for hepatitis C (HCV) antibody are eligible only if polymerase chain reaction
             is negative for HCV RNA.

          -  Subjects taking prohibited medications as described in Section 6.3.2. A washout period
             of prohibited medications for a period of at least 5 half-lives or as clinically
             indicated should occur before the start of treatment.