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9019 Background: NRAS mutant (mut) MM comprises a distinct, molecularly defined cohort of this disease that appears to have a poor prognosis compared to other genetic subsets. In contrast to BRAF mut MM, there are no effective small molecule inhibitors specifically targeting NRAS. Immune based therapy (IT) has become a mainstay in MM treatment, especially in BRAF wild type (WT) patients (pts). Biomarkers to predict which pts will benefit from IT have not been validated. The goal of this study was to evaluate whether genetic subtype (specifically NRAS) has a role in predicting benefit from IT in BRAF WT MM. Methods: We identified 173 pts from 3 institutions who underwent clinical genotyping (exome or PCR based) for NRAS and BRAF mutation from 1/09 – 8/12 and were treated with IT (defined as IL-2, ipilimumab (ipi), or anti-PD-1 (nivolumab, MK3475)/ PD-L1 (MPDL3280A)). Only BRAF WT pts were included. Primary endpoints were response rate (RR) and clinical benefit rate (CBR), defined as RR + stable disease lasting >24 wks to IT (best response as assessed by treating clinicians in any line of IT). Secondary endpoints were overall survival (OS) and progression-free survival (PFS) from first line IT. Results: Of the 173 pts, 59 had NRAS mut MM compared to 114 WT/WT (no mutation in NRAS or BRAF). Improved clinical outcomes were seen in the NRAS mut compared to WT/WT cohort in terms of RR (32% vs. 18%, p=0.042), and CBR (49% vs. 30%, p=0.012). Improvements in PFS and OS did not reach statistical significance. By specific IT, NRAS mutation predicted benefit compared to WT/WT for anti-PD-1/PD-L1 (RR 78% vs. 19%, p=0.002; CBR 78% vs. 29%, p=0.013, n=30) and ipi (RR 18% vs. 12%, p=0.315; CBR 41% vs. 22%, p=0.018, n=137). No significant differences were observed with IL-2 (RR 33% vs. 28%, p=0.730; CBR 33% vs. 39%, p=0.741, n=33). Conclusions: This study demonstrates that pts with NRAS mut MM achieve increased clinical benefit from IT compared to pts with BRAF/NRAS WT MM. A larger, prospective analysis is necessary to validate and expand on these results, including those with BRAF mut and KIT mut MM. However, our data suggest that NRAS mutation status may be a biomarker of response to IT in MM and that molecularly targeted immunotherapy may be feasible.