3512 Background: The combination of S and T is hypothesized to maximize pathway inhibition by concurrently targeting parallel signaling mechanisms and will abrogate potential resistance mechanisms directed towards the MAPK pathway through increased signaling via the survival pathway involving PI3K/Akt. Methods: Eligible patients (pts) were treated with escalating continuous oral doses of S (200 and 400 mg BID) and weekly T IV (15 mg, 25 mg). S began on day 8 of course 1 to permit PK evaluations of T. PD studies in PBMCs were performed serially in pts. Results: To date, 24 evaluable pts have received 85 courses [median 3;range1–12] in the following S/T dose cohorts; cohort 1: 200 mg/15 mg (n=6), cohort 2: 400 mg/15 mg (n=11), cohort 3: 400 mg/25 mg (n=6), and cohort 4: 200 mg/25 mg (n=1). Patients demographics were males/female 11/13, median age 54.5 [range 27–71] and PS of 0/1/2 : n=9/13/2. Dose limiting toxicities (DLT) were grade 3 typhlitis in 1/6 pts in cohort 1, and mucositis in 1/6 pts in cohort 2. Expansion of cohort 2 to 11 patients resulted in 4 additional DLTs (hand foot syndrome (HFS) x 2 pts, thrombycytopenia/rash x 1 pt, creatinine elevation x 1 pt). 3 of 6 pts in cohort 3 experienced DLT (HFS x 2 pts, thrombocytopenia x 1 pt). PK analyses show no evidence of S effect on T kinetics while Css,min values of S are consistent with those reported in single-agent studies (S 200mg BID median Css,min 4.42 μg/mL [SD 3.05], S 400 mg BID median Css,min 5.11 μg/mL [SD 4.35]). Apparent downregulation of 4E-BP1 and activated forms of p70S6 kinase and ERK was observed in some patients following treatment. Partial responses have occurred in NHL (1 pt) and papillary thyroid cancer (1 pt) and prolonged SD (> 12 mo) has been observed in RCC (1 pt). Conclusions: The combination of S and T demonstrate significant mucocutaneous toxicity at full doses of S, however preliminary PK analyses show no evidence of drug-drug interactions. Characterization of an intermediate dose of S 200 mg BID/T 25 mg IV is ongoing. [Table: see text]

Biomarkers have improved the clinical application of numerous targeted agents used to treat solid tumors. In melanoma, the finding that approximately 60% of tumor cells harbor specific Val600 mutations of BRAF has increased the likelihood of response to certain agents aimed at inhibiting the mutant kinase. While dabrafenib is an effective anti-tumor agent with acceptable tolerability in patients with BRAF-mutated melanoma, we report the development (and outcome) of a previously unpublished acute toxic reaction observed in a patient receiving the drug.