500 Exosomal microRNAs as putative predictive biomarkers for targeted therapy in stage IV cutaneous malignant melanoma

495 Hyperactive NRAS downstream signaling induces specific transcriptome changes eesiRNA based identification of new therapeutic targets in NRAS mutant melanoma identifies the noncoding RNA 7SL as a major proliferation enhancer I Vujic, M Vujic, M Sanlorenzo, C Posch, A Preschitz, R Esteve-Puig, K Lai, W Ho, K Rappersberger and S Ortiz-Urda 1 Dermatology, KA Rudolfstiftung, Vienna, Austria and 2 Dermatology, University of California, San Francisco, San Francisco, CA Benign naevi and malignant melanomas both can have oncogenic mutations in the NRAS gene but naevi only rarely progress to cancer. Such NRAS mutations should lead to specific transcriptome changes. The knowledge of these changes can A) identify new therapeutic targets and B) explain why some naevi have NRAS mutations but stay benign. Here, we introduce NRAS(Q61) mutant plasmids in a pool of human melanocytes to overactivate NRAS downstream pathways. We perform deep RNASeq and compare transcriptome changes in melanocytes with and without NRAS mutation. We list differentially expressed coding and noncoding transcripts by filtering our results with transcriptomes from 2 NRAS mutant melanoma cell lines and 89 NRAS mutant patient tumors. Next we use esiRNA (Endoribonuclease-prepared siRNA) libraries to knock down these transcripts and perform proliferation assays to identify potential targets. For most promising candidates we perform further siRNA knockdowns, cell based assays and take a closer look at their mechanistics. Our approach identified 237 transcripts, of which 2 coding and 6 noncoding transcripts played an important role in the proliferation of NRAS mutant melanoma. The knockdown of each of these transcripts led to cell proliferation decreases of 30-60%. We focused on the noncoding RNA RN7SL1 and identified its up-stream regulation (MAPK pathway) and its downstream effectors (p53). In conclusion, we identify new therapeutic targets which might be used in the battle against NRAS mutant melanoma. 496 Radiation therapy in melanoma patients with poor clinical characteristics e a collaborative experience with 107 patients C Posch, C Steffal, A Haider, B Flechl, T Kann, F Weihsengruber, A Schratter-Sehn and K Rappersberger 1 Dermatology, The Rudolfstiftung Hospital, Vienna, Austria and 2 Radiooncology, Kaiser-Franz-JOsef Hospital, Vienna, Austria Radiation therapy (RTX) is an important part of melanoma management. Even though it is effective for local disease control, the lack of improved overall survival often dampens enthusiasm for this therapeutic modality. We describe our collaborative experience treating 107 stage III and stage IV melanoma patients managed at a dermatology department and a radio-oncology center using therapeutic or adjuvant radiation. Our cohort comprised a subset of melanoma patients with unfavorable clinical characteristics (median Breslow thickness: 2.8mm (range 0.5-18mm); clinical stage at diagnosis: III+IV n1⁄495). The median age at diagnosis was 60.3 (13.6-90.0) years the median age at start of irradiation was 66.2 (20.691.5) years. The axillary area was the most frequent anatomical site for irradiation (n1⁄430) followed by bone irradiation (n1⁄420). The majority of patients received additional systemic therapy including immunotherapy (n1⁄460), chemotherapy (n1⁄450) and targeted therapy (n1⁄47). Average overall survival (OS) was calculated with 57.3 (SD 52.1) months. Average overall survival after RTX (OSaRTX) was 17.1 (SD 18.7) months. Loco-regional recurrence (LRR) of melanoma was observed in 17 irradiated areas. No difference in OS or OSaRTX and locoregional recurrence was found: OS without LRR 57.6 (SEM 5.7) years; OS with LRR 55.6 (SEM 9.2) years; OSaRTX without LRR 16.2 (SEM 1.8) years, OSaRTX with LRR 20.6 (SEM 3.8) years (all p>0.05). LDH serum levels did not correlate with local recurrence (r1⁄40.07). Subgroup analyses revealed that OSaRTX for axillary irradiation was 26.3 (SD 24.6) months. RTX was well tolerated with the majority of acute adverse events being grade 1 (CTCAE v4.02). 11 patients experienced late irradiation adverse effects (all grade 1; RTOG/EORTC score). From our data we conclude that RTX is a well-tolerated therapeutic modality with the potential for high local disease control, particularly in the axillary region.