Inclusion Criteria:

          -  All prior treatment-related toxicities must be Common Terminology Criteria for Adverse
             Events (CTCAE) (version 4.0) =< grade 1 (except alopecia) at the time of enrollment

          -  Absolute neutrophil count >= 1.5 x 10^9/L

          -  Hemoglobin >= 9 g/dL

          -  Platelets >= 100 x 10^9/L

          -  Prothrombin time (PT)/international normalized ratio (INR) =< 1.5 x upper limit of
             normal (ULN)

          -  Partial thromboplastin time (PTT) =< 1.5 x ULN

          -  Albumin >= 2.5 g/dL

          -  Total bilirubin =< 1.5 x ULN

          -  Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) =< 2.5 x ULN

          -  Creatinine =< 1.5 ULN or calculated creatinine clearance >= 50 mL/min or 24-hour urine
             creatinine clearance >= 50 mL/min

          -  Left ventricular ejection fraction (LVEF) >= lower limit of normal (LLN) by
             echocardiogram (ECHO) or multi gated acquisition scan (MUGA)

          -  Life expectancy of at least 3 months in the opinion of investigator

          -  Able to swallow and retain orally administered medication and does not have any
             clinically significant gastrointestinal abnormalities that may alter absorption such
             as malabsorption syndrome or major resection of the stomach or bowels

          -  Patient has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

          -  Ability to provide written informed consent obtained prior to participation in the
             study and any related procedures being performed

          -  Women of child-bearing potential (WOCBP) must have a negative pregnancy test within 14
             days of the first administration of study treatment, and counseled on
             contraception/abstinence while receiving the study treatment; urine human chorionic
             gonadotropin (HCG) is an acceptable pregnancy assessment

          -  A histologically confirmed rectal cancer with measurable or evaluable disease on
             imaging or endoscopy

          -  Stage II or III disease by the American Joint Committee on Cancer (AJCC) 7th edition

          -  Specific tumor genetic eligibility criteria include:

               -  Presence of KRAS gene mutation (at codon 12, 13, or 61) for patients on expansion
                  cohort.

               -  Presence of V600E BRAF gene mutation, or

               -  Presence of an NRAS mutation at codon 12, 13, or 61

        Exclusion Criteria:

          -  History of another malignancy; exception: subjects who have been disease-free for 5
             years, or subjects with a history of completely resected non-melanoma skin cancer or
             successfully treated in situ carcinoma are eligible

          -  Any serious and/or unstable pre-existing medical disorder (aside from malignancy
             exception above), psychiatric disorder, or other conditions that could interfere with
             subject's safety, obtaining informed consent or compliance to the study procedures, in
             the opinion of the Investigator

          -  Prior chemotherapy treatment unless > 5 years ago

          -  Prior treatment with a selective inhibitor of v-raf-1 murine leukemia viral oncogene
             homolog 1 (RAF) or mitogen-activated protein kinase kinase 1 (MEK)

          -  Prior radiation therapy to the abdomen or pelvis

          -  Have a known immediate or delayed hypersensitivity reaction or idiosyncrasy to drugs
             chemically related to study drug, or excipients or to dimethyl sulfoxide (DMSO)

          -  Current use of a prohibited medication

          -  History or current evidence / risk of retinal vein occlusion (RVO) or central serous
             retinopathy (CSR):

               -  History of RVO or CSR, or predisposing factors to RVO or CSR (e.g. uncontrolled
                  glaucoma or ocular hypertension, uncontrolled systemic disease such as
                  hypertension, diabetes mellitus, or history of hyperviscosity or
                  hypercoagulability syndromes)

               -  Visible retinal pathology as assessed by ophthalmic exam that is considered a
                  risk factor for RVO or CSR such as:

                    -  Evidence of optic disc cupping

                    -  Evidence of visual field defects

                    -  Intraocular pressure > 21 mm Hg

          -  Known human immunodeficiency virus (HIV), hepatitis B virus (HBV), or hepatitis C
             virus (HCV) infection (with the exception of chronic or cleared HBV and HCV infection
             which will be allowed)

          -  History or evidence of cardiovascular risk including any of the following:

               -  Bazett correction QT (QTcB) >= 480 msec

               -  History or evidence of current clinically significant uncontrolled arrhythmias;
                  exception: subjects with controlled atrial fibrillation for >30 days prior to
                  enrollment are eligible

               -  History of acute coronary syndromes (including myocardial infarction and unstable
                  angina), coronary angioplasty, or stenting within 6 months prior to enrollment

               -  History or evidence of current >= class II congestive heart failure as defined by
                  New York Heart Association (NYHA)

               -  Treatment refractory hypertension defined as a blood pressure of systolic > 140
                  mmHg and/or diastolic > 90 mm Hg which cannot be controlled by anti-hypertensive
                  therapy

               -  Patients with intra-cardiac defibrillators or permanent pacemakers

               -  Cardiac metastases

          -  Pregnancy or breastfeeding: women of child-bearing potential and men must agree to use
             adequate contraception (hormonal or barrier method of birth control; abstinence) prior
             to study entry and for the duration of study participation; should a woman become
             pregnant or suspect she is pregnant while participating in this study, she should
             inform her treating physician immediately; no breastfeeding while patient is on study