Inclusion Criteria:

          -  Diagnosis:

               -  Cohort A (frontline): Newly diagnosed AML

               -  Cohort B (relapsed/refractory): Relapsed/refractory AML or relapsed/refractory
                  MDS or chronic myelomonocytic leukemia (CMML) that is intermediate-2 or high-risk
                  by the International Prognostic Scoring System with >= 10% blasts harboring a Ras
                  pathway-activating mutation. Eligible mutations include: activating mutations of
                  KIT, HRAS/NRAS/KRAS, BRAF, CBL or PTPN11 or loss of function mutation of NF1.
                  Other mutations not listed here that are anticipated to activate Ras signaling
                  may be considered for enrollment after discussion with the principal investigator
                  (PI)

          -  Performance status =< 2 (Eastern Cooperative Oncology Group [ECOG] scale)

          -  Total serum bilirubin =< 2.5 x upper limit of normal (ULN), unless due to Gilbert's
             syndrome, hemolysis or the underlying leukemia approved by the PI

          -  Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) =< 3 x ULN, unless
             due to the underlying leukemia approved by the PI

          -  Creatinine clearance >= 30 mL/min

          -  Ability to swallow

          -  Signed informed consent

        Exclusion Criteria:

          -  Patients suitable for and willing to receive intensive induction chemotherapy (cohort
             A only)

          -  Active serious infection not controlled by oral or intravenous antibiotics (e.g.
             persistent fever or lack of improvement despite antimicrobial treatment)

          -  Patients with a prior or concurrent malignancy whose natural history or treatment is
             not anticipated to interfere with the safety or efficacy assessment of the
             investigational regimen may be included only after discussion with the PI

          -  Consumed strong inducer of CYP3A or p-glycoprotein within 3 days of study enrollment.
             Agents include but are not limited to: carbamazepine, phenytoin, rifampin, and St.
             John's wart

          -  Treatment with any investigational antileukemic agents or chemotherapy agents in the
             last 7 days before study entry, unless full recovery from side effects has occurred or
             patient has rapidly progressive disease judged to be life-threatening by the
             investigator. Prior recent treatment with corticosteroids, hydroxyurea and/or
             cytarabine (given for cytoreduction) permitted

          -  Pregnant women will not be eligible; women of childbearing potential should have a
             negative pregnancy test prior to entering on the study and be willing to practice
             methods of contraception throughout the study period and for at least 6 months after
             the last dose of study drugs. Women do not have childbearing potential if they have
             had a hysterectomy or are postmenopausal without menses for 12 months. In addition,
             men enrolled on this study should understand the risks to any sexual partner of
             childbearing potential and should practice an effective method of birth control
             throughout the study period and for at least 4 months after the last dose of study
             drugs. Lactating women (or those planning to breastfeed) should not breastfeed during
             treatment of trametinib and for at least 2 months after the last dose of trametinib