Screening ECG with a QTc > 460 msec confirmed by central lab prior to enrollment; congenital long QT syndrome; History of sustained ventricular tachycardia; History of ventricular fibrillation/torsades de pointes; Bradycardia defined as heart rate (hr) < 50 beats per minute; Patients with a pacemaker and hr >/= 50 beats per minute are eligible; Patients with a myocardial infarction or unstable angina within 6 mos of study entry; CHF (NYHA class III or IV); Right bundle branch block and left anterior hemiblock; Uncontrolled hypertension Concomitant use of drugs with a risk of causing torsades de pointes Concomitant use of CYP3A4, CYP1A2, or CYP2D6 substrates Unresolved diarrhea > CTCAE grade 1 Impairment of gastrointestinal (GI) function or GI disease that may significantly alter the absorption of Vemurafenib Other concurrent severe or uncontrolled medical conditions Patients who have received prior therapies will be allowed to enroll after a wash-out period: Chemotherapy - 3 week (wk) wash-out; Oral agents - 2 wk wash-out (Except Vemurafenib, no wash-out period); Investigational agents - 3 wk wash-out; Immunotherapy - 4 wk wash-out; Palliative radiation therapy to bone/brain - 2 wk wash-out; Major radiation or surgical procedure - 3 wk wash-out Concomitant use of any anti-cancer or radiation therapy. No measurable disease Pregnant, breast-feeding women or WOCBP not willing to use a double barrier method of contraception during the study and 3 months after the end of treatment. One method of contraception must be a barrier method. WOCBP are defined as sexually mature women who have not undergone a hysterectomy or have not been naturally postmenopausal for at least 12 consecutive months (who has had menses any time in the preceding 12 consecutive months).