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Abstract Intro: Multiple myeloma (MM) is an incurable malignancy that arises from MGUS, however the majority of patients with MGUS do not go on to develop MM. A deeper understanding of the biology of progression from MGUS to MM is needed to identify patients at higher risk of progression and identify potential strategies to prevent development of MM. Altered bone metabolism is common in MGUS with upregulation of the receptor-activator of nuclear kB ligand (RANKL) to osteoprotegrin (OPG) ratio. Vitamin D has a central role in bone metabolism and has recently been associated with progressive disease in several malignancies, including MM. We hypothesized that progressive alterations in the key molecules of bone remodeling would correlate with the risk group of MGUS and that correction of vitamin D deficiency would lead to improved equilibrium of selective cytokines involved in bone remodeling and metabolism. Methods: 43 patients with MGUS or smoldering myeloma were assigned to low (0 or 1 risk factor) or high (2 or 3 risk factors or smoldering multiple myeloma (SMM)) risk of progression to MM based on the IMWG consensus statement (Leukemia. 2010, June; 24(6); 1121-7). We measured 25 hydroxyvitamin D levels, IL-6, and the RANKL/OPG ratio via enzyme linked immunosorbent assay (ELISA). Patients with low levels of 25 hydroxyvitamin D were treated with 6,000 units of cholecalciferol daily for 8 weeks and then 2,000 units daily thereafter. Repeat levels of 25 hydroxyvitamin D, interleukin-6 (IL-6), and RANKL/OPG were repeated after three months of cholecalciferol therapy. Results: Total enrollment was 43 patients, with 26 patients with low risk disease and 17 patients with high risk disease. There was no significant difference in IL-6, OPG, RANKL, or the RANKL/OPG ratio levels between patients with low versus high risk disease. Patients with SMM versus patients with MGUS had higher levels of IL-6 RANKL and the RANKL/OPG ratio. 14 patients were found to have vitamin D deficiency with 25 hydroxyvitamin D <25ng/mL, 5 high risk and 9 low risk patients. There was no difference in IL-6 levels in patients with or without vitamin D deficiency. Patients with vitamin D deficiency had an increased RANKL and the RANKL/OPG ratio. With cholecalciferol supplementation in deficient patients, the average vitamin D level in deficient patients increased from 16.6 to 25.34 ng/mL while the RANKL/OPG ratio decreased (241.99 vs. 115.32, p-value .041) and the serum free light chain ratio improved (median improvement of 6, p-value=.013). Conclusions: These data provide clues that vitamin D deficiency is pervasive in MGUS . Additionally, hypovitaminosis D and its correction modulates the RANKL/OPG ratio that could play a pivotal role between osteoblasts and osteoclasts. Further study is required to determine if alterations in bone metabolism and the correction of abnormal metabolism can alter the disease course of patients with MGUS, especially serum free light chains and bone marrow plasma cells (PC) and the PC karyotype. This trial was conducted with IRB approval from the University of Kansas Medical Center. Table 1. RANKL, OPG, and RANKL/OPG ratios for SMM versus MGUS patients with 0,1, or two risk factors and patients with vitamin D deficiency versus those without vitamin D deficiency. SMM MGUS 0,1,2 p-value 25 hydroxyvitamin D<25 ng/mL 25 hydroxyvitamin D >25 p-value RANKL (pg/mL) 65500.76 13819.97 .041 50216.25 10387.77 .044 OPG (pg/mL) 180.59 164.81 .25 177.78 163.46 .60 RANKL/OPG 252.66 110.04 .06 241.99 73.25 .034 Disclosures Yacoub: seattle genetics: Membership on an entity's Board of Directors or advisory committees; sanofi: Membership on an entity's Board of Directors or advisory committees; alexion: Membership on an entity's Board of Directors or advisory committees. Mikhael:Onyx: Research Funding; Celgene: Research Funding; Sanofi: Research Funding; Novartis: Research Funding.

Abstract BACKGROUND: Pomalidomide-dexamethasone (Pom-Dex) represents an important therapeutic advance for the treatment of patients with relapsed/refractory multiple myeloma (MM). Nonetheless, patients with lenalidomide (Len) and bortezomib (double) refractory disease have a median progression-free survival of only 3.7 months with the combination, thus highlighting the need for further progress. Ixazomib, a novel, oral proteasome inhibitor, has pharmacodynamic properties that may allow for improved proteasome inhibition at the tumoral level and has synergistic activity in combination with IMiDs in preclinical MM models. Clinical studies have demonstrated activity as a single agent in relapsed/refractory MM and in combination with Len-Dex in newly diagnosed patients. We therefore evaluated the safety and preliminary efficacy of the combination of Pom, ixazomib and Dex in patients with Len and proteasome inhibitor (PI) refractory MM in the phase I portion of Alliance study A061202. METHODS: Key eligibility criteria included: relapsed or relapsed/refractory disease; ≥2 prior lines of therapy; double refractory disease (progression on or ≤60 days from the last dose of a Len- and PI-based therapy); ECOG performance status (PS) ≤2; absolute neutrophil count ≥1.0 x 109/L, platelets ≥50 x 109/L, creatinine clearance ≥50 mL/min; and ≤grade 2 peripheral neuropathy. Patients were treated with escalating doses of Pom and ixazomib utilizing a standard 3 + 3 dose escalation design in combination with standard dose Dex (Table 1). Patients received 2 - 4 mg of Pom on days 1 - 21; ixazomib 3 - 4 mg on days 1, 8 and 15; and Dex 40 mg (20 mg for those >75 years of age) on days 1, 8, 15 and 22 of a 28-day cycle. Patients were treated until disease progression or the development of unacceptable toxicity. RESULTS: Out of 17 evaluable patients, the median age was 64 (range 47 - 77) and the median time from diagnosis 5.5 years (range 3.3 - 8.3). Sixty-five percent, 24% and 12% had ISS stage 1, 2 and 3 disease at the start of treatment, respectively, and 65% had high-risk cytogenetics (gain of 1q, del[17p] and/or high-risk IgH translocation). All patients had an ECOG PS of 0 or 1 (59% and 41%, respectively). Of 14 patients with complete prior treatment data available, 100% had received prior Len, bortezomib and Dex, 71% alkylating agents (cyclophosphamide or low dose melphalan), 71% autologous stem cell transplant and 29% carfilzomib. Eighty-two percent were refractory to sequential Len- and bortezomib regimens, whereas 6% were refractory to a prior Len/proteasome inhibitor combination (12% not reported). Two dose limiting toxicities have occurred to date, 1 each at dose levels 3 and 4 (Table 1). Grade 3 and 4 neutropenia, thrombocytopenia and lymphopenia attributable to protocol therapy have been seen in 29%/6%, 12%/6% and 29%/0% of patients, respectively. Twelve percent of patients have experienced grade 3 infection, regardless of attribution, but none have experienced ≥grade 4 infection. The incidence of therapy-related peripheral neuropathy was 24%, none of which was ≥grade 3 in severity. Other common, therapy-related adverse events have included fatigue (53%), nausea (24%), constipation (18%), diarrhea (29%), rash (18%), tremor (24%), anxiety (18%), insomnia (29%) and edema (24%), all of which were ≤grade 2 in severity. Fifty-three percent of patients had at least 1 of the 3 medications dose reduced, and 35% experienced dose delays. To date, 1 patient has discontinued therapy due to adverse events and 1 due to refusal of further therapy. Of 13 patients receiving >1 cycle of therapy, the best overall response rate was 62% (7 partial responses, 1 very good partial response). CONCLUSIONS: The Pom, ixazomib and Dex combination has demonstrated an acceptable toxicity profile thus far with encouraging preliminary efficacy. Updated results of the phase I portion of the study will be presented at the meeting, including the maximum tolerated dose that will be used in the randomized, phase II portion of the study, in which the 3-drug combination will be compared with Pom-Dex in double refractory MM patients. ClinicalTrials.gov Identifier: NCT02004275. Supported by U10CA180821, U10CA180882. Table 1. Dose Level Pomalidomide Dose (mg) Ixazomib Dose (mg) DLT Evaluable DLTs 1 2 3 3 None 2 3 3 3 None 3 4 3 6 1 febrile neutropenia 4‡ 4 4 4 1 grade 4 thrombocytopenia lasting 8 days ‡enrollment into dose level 4 is complete. Disclosures Voorhees: Janssen, Celgene, GlaxoSmithKline, Onyx Pharmaceuticals and Oncopeptides: Consultancy, Research Funding; Array BioPharma, Celgene, GlaxoSmithKline, and Oncopeptides: Consultancy; Millennium/Takeda and Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Off Label Use: We will discuss the use of Ixazomib, an agent that is not FDA approved, in combination with pomalidomide and dexamethasone for the treatment of multiple myeloma.. Richardson:Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Gentium S.p.A.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Millennium Takeda: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees.

Abstract Background: No approved treatment options are available to HR-MDS pts after HMA therapy. Study 04-21 (“ONTIME” trial) was a Phase III, randomized, controlled study of the efficacy and safety of rigosertib, a novel small molecule inhibitor of PI3-kinase and PLK pathways, in a heterogeneous population of MDS pts who had relapsed after, failed to respond to, or progressed during administration of HMAs. The study was conducted at 87 sites in the United States and 5 European countries. Methods:From Dec 2010 to Aug 2013, 299 HR-MDS pts [<30% bone marrow blasts (BMBL)] who had progressed on (37% of total enrollment), failed to respond to (25%), or relapsed after (38%) HMA treatment were stratified on BMBL count and randomized 2:1 to receive rigosertib (199 pts) or BSC (100 pts). Rigosertib was administered at 1800 mg/24 hr for 72-hr as a continuous intravenous (CIV) ambulatory infusion, every 2 weeks for the first 16 weeks, and then every 4 weeks. The primary endpoint was overall survival (OS), analyzed on an intention-to-treat (ITT) basis using the Kaplan-Meier method stratified on BMBL (5% to 19% vs. 20% to 30%). The trial had a 95% power to detect a 13-wk increase in median OS from 17 wks on BSC, with a 2-sided alpha = 0.05. The following results are based on 242 deaths: 161 in the rigosertib arm and 81 in the BSC arm. Results : Overall, the 2 arms were balanced in terms of baseline characteristics, with the majority of pts being male (66%), and White (82%). Age ranged from 50-90 yrs in the rigosertib arm and 55-86 years in the BSC arm (median, 74 yrs). The majority of pts (85%) had an Eastern Cooperative Oncology Group (ECOG) score of 0 or 1. The median duration of the last HMA therapy was 8.8 months (mo) in the rigosertib arm and 10.3 mo in the BSC arm; 127 (64%) of rigosertib pts and 57% of BSC pts were classified as “primary HMA failure” (ie, they failed to respond to or progressed during HMA therapy, as defined by Prebet et al, J Clin Oncol, 2011). A 2.3-mo improvement in median OS was found in the overall (ITT) population (8.2 mo rigosertib vs. 5.9 mo BSC) (Figure 1). The ITT survival for rigosertib was similar to that noted in Phase I/II studies (35 weeks). The stratified log-rank p-value was 0.33. The stratified hazard ratio was 0.87, which was quite different from the ratio of medians (5.9/8.2 = 0.72), due to the fact that the 2 survival curves converged at 15 mo. Notably, among the 184 patients with primary HMA failure, the median OS was 8.6 mo in the rigosertib arm (N = 127) vs. 5.3 mo in the BSC arm (N = 57), HR= 0.69, p= 0.040 (Figure 2). Multivariate Cox regression, adjusting for pretreatment prognostic factors, showed little change in the treatment effect. The following subgroups were correlated with better OS: pts with failure of/progression on HMA treatment, pts with duration of HMA treatment ≤ 9 mo, pts < 75 years of age, and pts with very high risk per IPSS-R (Figure 3). Rigosertib was well tolerated, with a median dose intensity of 92%. There were no significant compliance or operations issues related to ambulatory continuous infusion. Protocol-defined dose reductions were reported in 5% of pts, with 24% experiencing dose delays of >7 days, mostly due to unrelated adverse events (AEs). No obvious differences between rigosertib and BSC were found in the incidence of AEs (rigosertib, 99%; BSC, 85%) or of ≥ Grade 3 AEs (rigosertib, 79%; BSC, 68%). In the rigosertib arm, AEs reported by ≥ 20% of pts, irrespective of severity or causality, were nausea (35%), diarrhea (33%), constipation (31%), fatigue (30%), fever (27%), anemia (22%), and peripheral edema (21%). Rigosertib had low myelotoxicity, consistent with previous clinical experience. Conclusions:Although the primary endpoint in this Phase III study of rigosertib vs BSC in pts with HR-MDS did not reach statistical significance in the ITT population, encouraging rigosertib treatment-related improvement in OS was noted in several subgroups of MDS pts, including those with “primary HMA failure and in patients in the IPSS-R Very High Risk category. CIV therapy with rigosertib had a favorable safety profile in this orphan population of elderly pts with MDS. Figure 1 Figure 1. Figure 2 Figure 2. Figure 3 Figure 3. Disclosures Fenaux: Celgene: Research Funding; Janssen: Research Funding; Novartis: Research Funding. Sekeres:Celgene Corp.: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Boehringer Ingelheim: Membership on an entity's Board of Directors or advisory committees. Roboz:Novartis: Consultancy; Agios: Consultancy; Celgene: Consultancy; Glaxo SmithKline: Consultancy; Astra Zeneca: Consultancy; Sunesis: Consultancy; Teva Oncology: Consultancy; Astex: Consultancy. Wilhelm:Onconova Therapeutics, Inc: Employment, Equity Ownership. Wilhelm:Onconova Therapeutics, Inc: Employment. Azarnia:Onconova Therapeutics, Inc: Employment. Maniar:Onconova Therapeutics, Inc: Employment.

Abstract Abstract 424 Background: Azacitidine for injection has been shown to prolong overall survival in patients (pts) with higher-risk myelodysplastic syndromes (MDS) compared with conventional care regimens (CCR) (Lancet Oncol, 2009). An oral formulation of azacitidine (CC-486) is in development. Oral azacitidine may maximize convenience, eliminate injection-site reactions, and if administered in extended dosing schedules, may enhance and prolong the therapeutic effects of azacitidine. Oral azacitidine administered once-daily (QD) for 7 days (d) of repeated 28d cycles has been shown to be bioavailable, biologically and clinically active, and well-tolerated in pts with MDS and acute myeloid leukemia (Garcia-Manero, J Clin Oncol, 2011). Preliminary evidence suggests that extending oral azacitidine dosing to 14d or 21d of the 28d cycle may enhance pharmacodynamic and epigenetic activity (Laille, Leuk Res, 2011). Purpose: To evaluate hematologic response and safety associated with extended dosing regimens of oral azacitidine in pts with lower-risk MDS. Methods: This ongoing, multicenter, phase 1 study, enrolled pts with lower-risk (IPSS Low or INT-1) MDS who were RBC transfusion dependent (TD) and/or thrombocytopenic (average platelet count ≤50,000 within 56d prior to the first dose) at baseline. Pts were sequentially assigned to receive oral azacitidine 300mg QD for either 14d or 21d of repeated 28d cycles. Hematologic assessments were made every 2 weeks. Hematologic response was assessed using IWG 2006 criteria (Cheson, Blood, 2006). Adverse events (AEs) were graded using NCI-CTCAE version 3.0. Results: At data cut-off (May 18, 2012), 53 pts with lower-risk MDS had enrolled (300mg oral azacitidine QDx14d, n=26; QDx21d, n=27). Demographic and disease characteristics at baseline were similar in the 14d and 21d treatment cohorts (Table 1). Median (range) hematology counts at baseline were Hgb 8.7 g/L (6.0–13.0), ANC 1.6×109/L (0–30.3), and platelets 56.0×109/L (6.0–564.0). At study entry, 40% of pts had received no prior MDS treatment (except transfusions), 45% had received erythropoiesis-stimulating agents, and 15% had received WBC growth factors. The number of oral azacitidine treatment cycles received ranged from 1 to 12 (median numbers of oral azacitidine cycles were 6 in the QDx14d and 4 in the QDx21d cohorts). Four pts in the 21d cohort and 1 pt in the 14d cohort received reduced oral azacitidine doses (200mg QD). Overall, 10 pts discontinued the study, including 6 pts (3 pts in each cohort) who discontinued due to AEs that may have been treatment-related (gastrointestinal [n=2] or intracranial [n=1] hemorrhage, febrile neutropenia [n=1], pneumonia [n=1], thrombocytopenia [n=1]). Overall response rates (ORR), which included complete (CR) and partial remission (PR), any hematologic improvement (HI), and transfusion independence (TI), ranged from 38.5% in the QDx14d cohort to 29.6% in the QDx21d cohort, and RBC TI was achieved by 47% and 33%, respectively, of pts who were RBC TD at baseline (Table 2). For pts who received at least 4 cycles of oral azacitidine (14d, n=19; 21d, n=14), ORR was 47.4% in the 14d and 50.0% in the 21d cohorts, and RBC TI rates in RBC TD pts (n=16) were 67% in the 14d and 57% in the 21d cohorts. The most frequent (≥5%) grade 3/4 hematologic AEs in the QDx14d cohort were anemia (11.5%), thrombocytopenia (11.5%), and neutropenia (7.7%); and in the QDx21d cohort were neutropenia (14.8%), anemia (7.4%), and febrile neutropenia (7.4%). Most frequent grade 3/4 non-hematologic AEs were gastrointestinal, including vomiting (7.7%) in the QDx14d cohort, and diarrhea (11.1%) and vomiting (7.4%) in the QDx21d cohort. Conclusions: Oral azacitidine 300mg QD administered in extended dosing schedules of 14d or 21d of repeated 28d cycles was effective and well-tolerated in these pts with lower-risk MDS. Beside hematologic AEs, the most frequently observed AEs with oral azacitidine were gastrointestinal and were manageable. Efficacy and safety outcomes with 300mg QD oral azacitidine were generally comparable between the 14d and 21d extended dosing regimens. Based on these data, oral azacitidine administered once-daily in extended dosing schedules is active and well-tolerated and warrants further investigation in randomized, controlled trials. Disclosures: Garcia-Manero: Celgene: Research Funding, Speakers Bureau. Gore:Celgene Corporation: Consultancy, Research Funding. Scott:Celgene Corporation: Honoraria, Research Funding, Speakers Bureau. Hetzer:Celgene Corporation: Employment, Equity Ownership. Kumar:Celgene Corporation: Employment, Equity Ownership. Skikne:Celgene: Employment, Equity Ownership.

Abstract Background: Standard treatment for stage III melanoma is surgery followed by consideration of adjuvant therapy. This strategy is inadequate for high-risk stage III patients who have a substantial risk of subsequent relapse and distant metastasis. The goals of this trial are to improve oncologic outcomes, assess treatment response and spare patients with poorly responsive, rapidly metastatic disease from a futile operation. This protocol based on the hypothesis that treatment before surgery will immunize patients against his or her own unique tumor. While new drugs are now FDA-approved for adjuvant treatment of stage III melanoma, outcomes are still suboptimal in high-risk patients. The neoadjuvant approach is largely untested and preclinical data suggest neoadjuvant therapy is more effective than adjuvant immunotherapy. While targeted therapies can be rapidly effective, immunotherapy responses, when they occur, tend to be much more durable, prompting this study. Our specific strategy is based on the fact that BRAFm melanoma patients benefit both from BRAF/MEK inhibition (vemurafenib/cobimetinib) and PD-1 axis inhibition (atezolizumab) while patients with BRAFwt melanoma benefit from PD-1 axis inhibition (atezolizumab) and intermittent MEKi (cobimetinib) may increase effector function in tumor-infiltrating T cells. A second component of the study is robust evaluation of biomarkers of response, toxicity and outcome. Specific correlatives include assessment of the predictive value of Bim levels in tumor-related T cells, correlation of sPD-L1 with efficacy and toxicity, correlation of PD-L1 expression with efficacy, and determination of key relationships between tumor and immune cells via mIHC spatial analysis, gene expression profiles and microbiome associations with clinical response. Methods: The NeoACTIVATE trial enrolls melanoma patients with resectable clinically detectable nodal metastases (by physical examination or imaging), dual nodal basin disease or nodal recurrence of melanoma. Neoadjuvant systemic therapy is based on BRAF mutation status; participants receive either vemurafenib, cobimetinib and atezolizumab (vem/cobi/atezo), or cobimetinib and atezolizumab (cobi/atezo) before surgery. Following surgery, all patients receive atezo immunotherapy. The primary aim of the study is RFS estimates for each cohort. Secondary aims are safety/toxicity, pathologic complete response rate and prospective evaluation of biomarkers of treatment response and toxicity. This study is significant in that it is the first to test 1) combined of targeted and immunotherapy in the neoadjuvant setting for patients with resectable Stage III melanoma and 2) the novel combination of MEK-inhibition with immunotherapy in the neoadjuvant setting for resectable Stage III melanoma. As of January 1, 2019, 10% of planned patients have been enrolled and enrollment continues. Citation Format: Tina J. Hieken, Vera J. Suman, Shernan G. Holtan, Thomas J. Flotte, Lisa A. Kottschade, Matthew S. Block. Neoadjuvant combination targeted and immunotherapy for high-risk resectable stage III melanoma (NeoACTIVATE), NCT03554083 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT121.

e21039 Background: Tumor-infiltrating neutrophils (TINs) and their myeloid precursors play an important role in cancer biology. While activated neutrophils have been shown to kill tumor cells, there is growing evidence that neutrophils may also support tumor progression by impairing T cell-dependent anti-tumor immunity. We hypothesized that low TINs would be associated with better responses to immunotherapy (IO). Methods: Pretreatment biopsies from 15 metastatic melanoma (MM) pts treated with anti-CTL4 and anti-PD-1 therapy from 2012-17 were collected and stained with myeloperoxidase (MPO). Slides were scanned at 40x magnification on the Aperio ScanScope AT Turbo brightfield instrument (Leica Biosystems) at a resolution of 0.25 microns per pixel. To indicate the region of analysis, the digital pen tool was used to trace a minimum 85% of tumor. Ten fixed-sized boxes were placed on the hottest staining region in a second annotation layer on the image. The boxes equaled 1mm2 in total area. If the tumor tracing had an area of 1mm2, or less, boxes were not placed on the image. The selected tissue was analyzed using an Aperio imaging quatification algorithm . The number of 3+ cells were considered positive for neutrophils and used in subsequent calculations. Quality control review was performed on a subset of cases by Anatomic Pathologists. Response to therapy was assessed using the Response Evaluation Criteria In Solid Tumors (RECIST). Overall survival (OS) was calculated using the Kaplan Meier method. Results: The median number of treatment lines before the biopsy was 1 (range 0-2). The treatment immediately following the biopsy consisted of ipilimumab (n = 10, 66.6%), pembrolizumab (n = 4, 26.6%), ipilimumab/nivolumab (n = 1, 6.6%). The median number of neutrophils in the biopsy hotspot was 92/mm2 (range 6-219) for the entire cohort. For patients achieving PR and CR after 4 cycles of therapy, the median neutrophils were 36/mm2 (IQ 14-78) while the median was 106/mm2 (IQ 60-138) for patients who had progressive disease,( p = 0.04). There was no correlation between the numbers of neutrophils in the biopsy with the absolute neutrophil count in the peripheral blood (R value: 0.012). Conclusions: Decreased TINs are significantly associated with better responses to IO in MM pts. Measurements of TINs may help to select patients who are likely to benefit from anti-CTL4 and anti-PD-1 therapy. Additionally, exploration of whether combining therapies that decrease neutrophils intratumorally should be explored.

9535 Background: A broad understanding of baseline immunity is needed in order to predict responses to PD-1 blockade. We previously reported in a preclinical model that elevated Th1 signature cytokines are present after successful therapy with PD-1 blockade. In this study we evaluated serum cytokines as biomarkers of response in a cohort of patients with metastatic melanoma undergoing anti-PD1 therapy. Methods: 27 pts diagnosed with metastatic melanoma (MM) received anti-PD-1 therapy and had peripheral blood collected prior to anti-PD-1 therapy start and 12 weeks after; 55 proinflammatory-related serum cytokines were analyzed at both times using the Meso Scale Discovery (MSD) assay. At week 12, we identified 15 pts who had radiographic complete or partial response (TR) and 12 had progressive disease (PD) using RECIST criteria. Spearman rank correlation coefficients (rho) were used to assess association between pre-treatment serum cytokine levels. For each cytokine, differences in pretreatment serum levels and the ratio of the 12 week to pre-treatment serum levels between TR and PD groups were assessed using Wilcoxon rank sum tests. Results: Pretreatment serum IL-12p40 and MIP3a (CCL20) were moderately correlated (rho=0.3944). Pretreatment IL-12p40 and was found to be significantly higher (p=0.0025) in the TR group (median=48.5; 25th to 75th percentile [IQR]:25.3-63.8) relative to the PD group (median=17.3; IQR: 8.6-30.3). Pretreatment MIP3a was also found to be significantly higher (p=0.0359) in the TR group (median=1.72; IQR: 1.41-2.65) relative to the PD group (median=1.33; IQR: 1.09-1.98). The 12th week pretreatment IL-12p40 ratio (median=1.98; IQR: 1.4-11.3) in the TR group was greater than that (median=0.64; IQR: 0.23-1.61) in the PD group (p=0.0029); we identified that baseline serum levels >15pg/ml of IL12p40 prior to immunotherapy were associated with significantly prolonged event free survival (p=0.001). Conclusions: Measurements of IL-12p40 and MIP-3a levels before immunotherapy may help to select patients who are likely to benefit from anti-PD1 therapy. Additionally, exploration of combination therapies that increase IL-12P40 and MIP3 prior or during immunotherapy should be undertaken.