8517 Background: Vemurafenib, a BRAF inhibitor, is associated with improved PFS and OS in patients (pts) with BRAF^V600-mutant metastatic melanoma (mM). We present preliminary safety and efficacy findings from a safety study of vemurafenib in pts with unresectable stage IIIC/IV mM with BRAF^V600 mutations. Methods: Pts with untreated or previously treated stage IIIC/IV BRAF^V600 mutation-positive (cobas 4800 BRAF V600 Mutation Test) melanoma were enrolled. Pts received continuous oral vemurafenib 960 mg bid. Primary study endpoint was safety; efficacy (RECIST V 1.1) was a secondary endpoint. Results: Of 1,964 screened pts between Mar and Sep 2011, 914 (47%) were enrolled and 834 were evaluable for safety. Median age was 53 (21–88 years), 55% males. Median time since first mM diagnosis was 7.6 months (0–18 years). At baseline, 80% of pts had ECOG PS 0–1, 11% ECOG PS 2 (missing 9%); 27% of pts had brain metastases, and 31% had elevated LDH. Most pts had received prior systemic therapy (70%) including ipilimumab (14%), MEK and BRAF inhibitors (2%). At data cut-off (Sep 30, 2011), median treatment duration was 68 days (1–223 days) with 87% of pts still on treatment. Of 834 pts, 553 (66%) to date have reported AEs. Of 553 pts reporting AEs, 88% were related to vemurafenib, 33% Grade 3, and 1.9% Grade 4. The most common (>1%) Grade 3/4 AEs were rash (3.6%), arthralgia (3.1%), and cutaneous squamous cell carcinoma/keratoacanthoma (4.3%). Most common AEs (>10%) of any grade were arthralgia (31%), rash (29%), fatigue (22%), photosensitivity (21%), nausea (15%), and were similar irrespective of brain metastases and ECOG PS. AEs caused treatment interruption in 141 (17%) pts. Of 109 pts who discontinued treatment (13%), main reasons for withdrawal were progressive disease (60%), death (20%), AEs (6%; most commonly arthritis and abdominal pain). Tumor assessments at Week 8 of treatment were available for 302/834 (36%) pts, 61% pts achieved CR or PR, and 29% had SD. Conclusions: In a setting representative of routine clinical practice, vemurafenib is seen to be well tolerated and both safety profile and activity resemble the phase I–III data although this analysis is limited by the study duration.