Inclusion Criteria:

- Must be at least 18 years of age

- Must have histologically confirmed cutaneous metastatic melanoma (Stage IV) that is
BRAF mutation-positive (V600 E/K) as determined via central testing with a BRAF
mutation assay.

- Is treatment naive or has received prior treatment for metastatic melanoma.

- Must have measurable disease according to Response Evaluation Criteria in Solid
Tumors (RECIST 1.1).

- Women of child-bearing potential must have a negative pregnancy test within 14 days
prior to the first dose of study treatment.

- Women with reproductive potential must be willing to practice acceptable methods of
birth control during the study and for up to 4 weeks after the last dose of study
medication.

- Men with reproductive potential must be willing to practice acceptable methods of
birth control during the study and for up to 16 weeks after the last dose of study
medication.

- Must have Eastern Cooperative Oncology Group (ECOG) Performance Status of 0-1.

- Adequate organ function.

Exclusion Criteria:

- Previous treatment with a BRAF or MEK inhibitor.

- Cancer therapy (chemotherapy with delayed toxicity, radiation therapy, immunotherapy,
biologic therapy, or major surgery) within the last 3 weeks; chemotherapy regimens
without delayed toxicity within the last 2 weeks; or use of any investigational
anti-cancer or other drug within 28 days or 5 half-lives, whichever is longer,
preceding the first dose of GSK2118436.

- A history of known Human Immunodeficiency Virus (HIV), Hepatitis B Virus (HBV), or
Hepatitis C Virus (HCV) infection.

- History or evidence of brain metastases on MRI or head CT if MRI is not able to be
performed.

- History of other malignancy. 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.

- Certain cardiac abnormalities.