Melanoma Cohort Research Articles

Abstract 397: ECM2 mutation can serve as a potential efficacious predictor of immunotherapy in melanoma patients

Abstract Background: Epithelial-mesenchymal transition (EMT) has been reported to play a pivotal role in tumor immunosuppression and immune evasion. In multiple solid tumors, PD-L1 expression was much higher in “mesenchymal” compared with that in “epithelial”, indicating patients with mesenchymal phenotypes are more likely to benefit from PD-1/PD-L1 immunotherapy. ECM2 encodes a putative extracellular matrix protein, which involves in cell-cell and/or cell ECM recognition processes, thereby may affecting EMT. However, the predictive value of ECM2 in cancer immunotherapy has not been revealed. Method: Seven independent public cohorts of NSCLC, melanoma, and pan-cancer, including Rizvi, Van Allen, MSKCC, OAK/POPLAR, Miao, and Samstein cohorts were used to investigate the correlation between ECM2 mutation and clinical events, such as objective response rate (ORR), overall survival (OS), and progression free survival (PFS). Result: Across all the analyzed cancer types, ECM2 mutation has a strong connection with better outcomes to immune checkpoint inhibitors only in melanoma cancer. ECM2-mutated group was significantly associated with higher ORR (75.0% vs 13.9%, P = 0.013), longer OS (35.9 months vs 8.5 months, 95% CI, 0.02-1.09, P = 0.032) than ECM2-wide-type group. PFS between these two groups was comparable (8.15 months vs 2.8 months, 95% CI, P = 0.25). Furthermore, melanoma patients harboring ECM2 mutation exhibited significantly higher TMB compared with ECM2-wide-type patients in Van Allen cohort (1279.5 mut/Mb vs 125.5 mut/Mb, P = 0.0056). Conclusion: This study demonstrated that ECM2 mutation can serve as a potential predictor for a favorable response to ICIs in melanoma patients. Citation Format: Qitao Yu, Aiping Zeng, Yun Zhao, Xiaochun Huang, Wenzhuan Xie, Mengli Huang, Ting Bei. ECM2 mutation can serve as a potential efficacious predictor of immunotherapy in melanoma patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 397.

Abstract CT035: Safety/tolerability and preliminary antitumor activity of sitravatinib plus tislelizumab in patients with PD-(L)1 refractory/resistant unresectable or metastatic melanoma from a phase 1b study

Abstract Background: While PD-(L)1 inhibitors have improved outcomes for melanoma, a substantial proportion of patients do not respond or develop resistance. Sitravatinib, a spectrum-selective TKI targeting TAM receptors (Tyro3/Axl/MerTK) and VEGFR2, reduces the number of myeloid-derived suppressor cells and regulatory T cells while increasing the ratio of M1/M2-polarized macrophages, which may overcome an immunosuppressive tumor microenvironment and augment antitumor immune responses. Tislelizumab, an anti-PD-1 antibody engineered to minimize binding to FcγR on macrophages to abrogate antibody-dependent phagocytosis, has shown clinical activity as a single agent and in combination with chemotherapy in patients with advanced solid tumors, including melanoma. Methods: We report results from the melanoma cohort of an ongoing multicohort phase 1b study (BGB-900-103; NCT03666143) assessing safety/tolerability and preliminary antitumor activity of sitravatinib + tislelizumab in advanced solid tumors. Eligible patients had unresectable or metastatic melanoma refractory/resistant to PD-(L)1 inhibitors and had not received other prior immunotherapy (eg, anti-CTLA-4, -OXO40, or -CD137) or anti-BRAF/MEK therapy. Patients received oral sitravatinib 120 mg once daily and tislelizumab 200 mg IV Q3W until a discontinuation criterion was met. The primary endpoint was safety/tolerability; key secondary endpoints included investigator-assessed objective response rate (ORR), disease control rate (DCR), and progression-free survival (PFS). Results: As of Oct 13, 2020, 25 patients were enrolled; 16 patients (64%) remained on treatment. All patients received 1 prior line of PD-(L)1 therapy, median age was 51 years (range: 23-79), and baseline histology included cutaneous (n=12; 48%), acral (n=7; 28%), and mucosal (n=4; 16%) subtypes. Median duration of study follow-up was 5.5 months (range: 1.5-13.3). Adverse events (AEs) were reported in 25 patients (100%); the most commonly reported grade ≥3 AE was hypertension (n=3; 12%). Serious AEs were reported in 4% (n=1/25) of patients. Dose reductions of sitravatinib due to AEs occurred in 13 patients. No AEs led to death. Six patients achieved a confirmed partial response. Confirmed ORR was 24.0% (95% CI: 9.36-45.13); DCR was 88.0% (95% CI: 68.78-97.45). Median PFS was 6.7 months (95% CI: 4.07, not evaluable). Conclusions: Sitravatinib + tislelizumab was generally well tolerated, had a manageable safety/tolerability profile, and demonstrated preliminary antitumor activity in patients with refractory/resistant unresectable or metastatic melanoma. Further investigation of sitravatinib + tislelizumab in these patients is warranted. Citation Format: Chuanliang Cui, Hongming Pan, Matteo Carlino, Jiuwei Cui, Xuan Wang, Cheng Chen, Xiao Xiang, Liu Yang, Jun Guo. Safety/tolerability and preliminary antitumor activity of sitravatinib plus tislelizumab in patients with PD-(L)1 refractory/resistant unresectable or metastatic melanoma from a phase 1b study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT035.

Abstract 2157: Potential correlations between PLK1, BRAF and MITF in melanoma

Abstract Melanoma is one of the most aggressive types of cancer and extremely difficult to treat after metastasis. BRAFV600E-activating mutations give rise to ∼80% of melanocytic nevi, yet only one-third of melanocytic nevi result in melanoma, suggesting the involvement of other factors. Polo-like kinase 1 (PLK1), an important regulator of cell cycle progression, is overexpressed in melanoma and its expression has been shown to correlate with patient prognosis. Microphthalmia-associated transcription factor (MITF) is a melanocytic lineage-specific transcription factor that regulates a variety of genes critical for melanin synthesis as well as melanoma progression. The goal of this study was to define potential interactions between PLK1, BRAFV600E, and MITF in human melanoma. First, we employed a commercially available human tissue microarray (TMA) coupled with high-throughput, multispectral Vectra scanning and inForm analysis to study a number of clinical tissue cores (nevus, malignant and metastatic melanoma). The TMA was simultaneously immunostained for PLK1, BRAFV600E, MITF, proliferation marker Ki67, melanoma biomarker S100 and DAPI, and was subjected to Vectra scanning and inForm analyses. Using Simple Linear Regression analyses, we found significant correlations among each pair of the selected four proteins (PLK1, BRAFV600E, MITF and Ki67) with correlation co-efficient ranging 0.24-0.84. To analyze if PLK1, and BRAFV600E are contributing to cell proliferation (Ki67 expression) or affecting MITF expression, we employed a Multiple Linear Regression analysis. Our data suggested that high expressions of both BRAFV600E and PLK1 are correlated positively with the expression of Ki67. However, when fitting both PLK1 and BRAFV600E versus MITF, only high PLK1 had significant positive correlation with MITF, while BRAFV600E did not show correlation with MITF. These results suggest that PLK1 and MITF could contribute to melanoma progression independent to BRAFV600E. To further validate our findings, we analyzed The Cancer Genome Atlas (TCGA) database containing a large melanoma cohort of 432 melanoma patients with information on overall survival (OS). To visualize the survival plots, the expression level of PLK1 and MITF was sorted and equally separated to two groups using the median value as a cutoff. Kaplan-Meier analyses showed that high mRNA expression of both PLK1 and MITF were individually associated with significant reductions in OS. Interestingly, when we sorted the data for both high PLK1 and high MITF in the same patient, the OS was shorter than that of patients with low PLK1 and low MITF. Overall, our study suggests an association between PLK1 and MITF pathways during melanoma progression, which may affect overall survival in melanoma patients. Thus, concomitant targeting of PLK1 and MITF could provide an advantage over monotherapy towards melanoma management. However, in-depth studies are required to validate our findings. Citation Format: Gagan Chhabra, Shengqin Su, Chandra K. Singh, Mary A. Ndiaye, Nihal Ahmad. Potential correlations between PLK1, BRAF and MITF in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2157.

Abstract 29: The recently approved high-TMB criteria may introduce a sex bias in response to PD1 inhibitors

Abstract Motivation and research question: The U.S. Food and Drug Administration recently approved treatment with pembrolizumab, an immune checkpoint inhibitor (ICI) targeting PD1 (anti-PD1), for all advanced solid tumors with high tumor mutational burden (TMB), defined as ≥10 mutations/Megabase (mut/Mb). Recent studies have suggested that strength of immune selection, biomarkers of outcome, TMB levels and response to ICI treatment may differ between male and female cancer patients in some tumor types. This motivated us to examine what are the sex-specific implications, if any, of the ≥10 mut/Mb threshold on selecting patients for ICI treatment. Data & Methods: We analyzed the largest ICI cohort publicly available to date (Samstein et al. 2019), including 1,070 patients treated with anti-PD1/PD-L1 monotherapy, 99 treated with anti-CTLA4 and 255 treated with an ICI combination. We focused on the nine solid tumor types with TMB and clinical response data (median follow-up of 19 months) for at least 50 patients. Results: 1.We observed a significant difference in the median TMB across sex among melanoma patients (n=130, female vs male median TMB=8.36 vs 11.81, P<0.02), in concordance with previous observations.2.Notably, we found that the FDA-approved threshold of ≥10 mut/Mb to select patients would result in an unwarranted sex bias in melanoma patients. This threshold successfully identifies female melanoma patients with better overall survival (hazard ratio (HR) =0.19, P<0.03) but fails to do so in male patients (HR=0.94, P<0.85), resulting in a five times higher HR in males vs females at that threshold level (interaction between sex and TMB P<0.03). This bias in effect size by sex is confirmed in two additional melanoma cohorts treated with anti-PD1 (Hugo et al. 2016, N=38, P<0.024; Liu et al. 2016, N=114, P<0.03; and P<0.01 for all three melanoma datasets combined, N=312). We do not observe this differential effect for anti-CTLA4 treatment (P<0.14, N=174) or for anti-PD1 + anti-CTLA4 combination (P<0.8, N=115) or for non-ICI treatments (P<0.4, N=322).3.Analysis of additional eight cancer types whose data are available in (Samstein et al 2019) points to glioblastoma (female vs male HR=0.87 vs 0.5) and cancer of unknown origin (female vs male HR= 1.03 vs 0.15), which show marked differences in the HR between male and female patients when applying the FDA threshold for TMB. However, despite these large effects, they do not achieve statistical significance, probably due to the small size of these datasets. Conclusions: The FDA-approved criteria of 10 mutations/Mb could serve as an informative biomarker for stratifying female melanoma patients but is inadequate for stratifying male patients for anti-PD1 treatment. Our results indicate that its usage is likely to introduce a sex bias in additional cancer types, which will be highly important to carefully test further in larger datasets. Citation Format: Neelam Sinha, Sanju Sinha, Kuoyuan Cheng, Sanna Madan, Alejandro Schaffer, Kenneth Aldape, Ayelet Erez, Brid M. Ryan, Eytan Ruppin. The recently approved high-TMB criteria may introduce a sex bias in response to PD1 inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 29.

De Novo Mutation in Non-Tyrosine Kinase Domain of ROS1 as a Potential Predictor of Immune Checkpoint Inhibitors in Melanoma.

PurposeDespite the success of targeted therapy in c-ros oncogene 1 (ROS1)-rearranged cancers, especially non-small cell lung cancer (NSCLC), the clinical significance of ROS1 de novo mutation has not yet been understood. We sought to elucidate the predictive effect of ROS1 mutation for immune checkpoint inhibitor (ICI) therapy in melanoma.MethodsThe Cancer Genome Atlas [TCGA (n = 10967)] and Memorial Sloan Kettering Cancer Center [MSK (n = 10,945)] datasets, as well as two clinical cohorts of melanoma received ICI [CA209-038 (n = 73) and MEL-IPI (n = 110)], were included to explore the prevalence, prognostic effect, and immunotherapeutic predictive effect of ROS1 mutation in melanoma. Overall survival (OS) was defined as the primary outcome.ResultsOverall, melanoma accounted for the highest proportion of ROS1 mutation (~20%) which made up the majority (~95%) of the ROS1-alterated cases. Remarkably, ROS1 mutation yielded longer OS from ICI than the wild-type counterpart in the MSK melanoma population [hazard ratio (HR) 0.47, 95% confidence interval (CI) 0.30–0.74], and two external melanoma cohorts (CA209-038: HR 0.42, 95% CI 0.20–0.89; MEL-IPI: HR 0.55, 95% CI 0.34–0.91), without affecting the prognosis of patients. Elevated tumor mutational burden and enrichment of DNA damage repair was observed in ROS1 mutated patients, providing an explanation for the favorable responses to ICI therapy. Precisely, ROS1 mutation in non-protein tyrosine kinase (PTK) domain but not PTK mutation was responsible for the immunotherapy-specific responses of the ROS1 mutated patients in melanoma.ConclusionsCollectively, ROS1 mutation, specifically the non-PTK mutation, is a potential predictor of ICI therapy in melanoma, which is distinct from the well-established role of ROS1 rearrangement for targeted therapy in NSCLC.

Silencing PEX26 as an unconventional mode to kill drug-resistant cancer cells and forestall drug resistance

ABSTRACT Promoting the macroautophagy/autophagy-mediated degradation of specific proteins and organelles can potentially be utilized to induce apoptosis in cancer cells or sensitize tumor cells to therapy. To examine this concept, we enriched for autophagosomes from histone deacetylase inhibitor (HDACi)-sensitive U937 lymphoma cells and isogenic HDACi-resistant cells. Mass spectrometry on autophagosome-enriched fractions revealed that HDACi-resistant cells undergo elevated pexophagy, or autophagy of the peroxisome, an organelle that supports tumor growth. To disturb peroxisome homeostasis, we enhanced pexophagy in HDACi-resistant cells via genetic silencing of peroxisome exportomer complex components (PEX1, PEX6, or PEX26). This consequently sensitized resistant cells to HDACi-mediated apoptosis, which was rescued by inhibiting ATM/ataxia-telangiectasia mutated (ATM serine/threonine kinase), a mediator of pexophagy. We subsequently engineered melanoma cells to stably repress PEX26 using CRISPR interference (CRISPRi). Melanoma cells with repressed PEX26 expression showed evidence of both increased pexophagy and peroxisomal matrix protein import defects versus single guide scrambled (sgSCR) controls. In vivo studies showed that sgPEX26 melanoma xenografts recurred less compared to sgSCR xenografts, following the development of resistance to mitogen-activated protein kinase (MAPK)-targeted therapy. Finally, prognostic analysis of publicly available datasets showed that low expression levels of PEX26, PEX6 and MTOR, were significantly associated with prolonged patient survival in lymphoma, lung cancer and melanoma cohorts. Our work highlighted that drugs designed to disrupt peroxisome homeostasis may serve as unconventional therapies to combat therapy resistance in cancer. Abbreviations: ABCD3/PMP70: ATP binding cassette subfamily D member 3; ACOX1: acyl-CoA oxidase 1; AP: autophagosome; COX: cytochrome c oxidase; CQ: chloroquine; CRISPRi: clustered regularly interspaced short palindromic repeats interference; DLBCL: diffuse large B-cell lymphoma; GO: gene ontology; dCas9: Cas9 endonuclease dead, or dead Cas9; HDACi: histone deacetylase inhibitors; IHC: Immunohistochemistry; LAMP2: lysosomal associated membrane protein 2; LCFAs: long-chain fatty acids; LFQ-MS: label-free quantitation mass spectrometry; LPC: lysophoshatidylcholine; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; PBD: peroxisome biogenesis disorders; PTS1: peroxisomal targeting signal 1; ROS: reactive oxygen species; sgRNA: single guide RNA; VLCFAs: very-long chain fatty acids; Vor: vorinostat; WO: wash-off.

Immune Monitoring in Melanoma and Urothelial Cancer Patients Treated with Anti-PD-1 Immunotherapy and SBRT Discloses Tumor Specific Immune Signatures.

Simple SummaryCurrently available biomarkers for response to checkpoint inhibitors are incomplete and predominantly focus on tumor tissue analysis e.g., tumor mutational burden, programmed cell death-ligand 1 (PD-L1) expression. Biomarkers in peripheral blood would allow a more dynamic monitoring and could offer a way for sequential adaptation of treatment strategy. We conducted an in-depth analysis of baseline and on-treatment systemic immune features in a cohort of stage III/IV melanoma and stage IV urothelial cancer (UC) patients treated with anti-programmed cell death-1 (anti-PD-1) therapy combined with stereotactic body radiotherapy (SBRT) in a similar regimen/schedule. Baseline immunity was clearly different between these two cohorts, indicating a less active immune landscape in UC patients. This study also detected signatures of proliferation in the CD8+ T-cell compartment pre-treatment and early after anti-PD-1 initiation that were positively correlated with clinical outcome in both tumor types. In addition our data support the biological relevance of PD-1/PD-L1 expression on circulating immune cell subsets, especially in melanoma.(1) Background: Blockade of the PD-1/PD-L1 pathway has revolutionized the oncology field in the last decade. However, the proportion of patients experiencing a durable response is still limited. In the current study, we performed an extensive immune monitoring in patients with stage III/IV melanoma and stage IV UC who received anti-PD-1 immunotherapy with SBRT. (2) Methods: In total 145 blood samples from 38 patients, collected at fixed time points before and during treatment, were phenotyped via high-parameter flow cytometry, luminex assay and UPLC-MS/MS. (3) Results: Baseline systemic immunity in melanoma and UC patients was different with a more prominent myeloid compartment and a higher neutrophil to lymphocyte ratio in UC. Proliferation (Ki67+) of CD8+ T-cells and of the PD-1+/PD-L1+ CD8+ subset at baseline correlated with progression free survival in melanoma. In contrast a higher frequency of PD-1/PD-L1 expressing non-proliferating (Ki67−) CD8+ and CD4+ T-cells before treatment was associated with worse outcome in melanoma. In UC, the expansion of Ki67+ CD8+ T-cells and of the PD-L1+ subset relative to tumor burden correlated with clinical outcome. (4) Conclusion: This study reveals a clearly different immune landscape in melanoma and UC at baseline, which may impact immunotherapy response. Signatures of proliferation in the CD8+ T-cell compartment prior to and early after anti-PD-1 initiation were positively correlated with clinical outcome in both cohorts. PD-1/PD-L1 expression on circulating immune cell subsets seems of clinical relevance in the melanoma cohort.

PREX2 mutation serves as a novel predictor of response to anti-PD-1/PD-L1 treatment in melanoma.

e21504 Background: Melanoma is notable for its metastatic propensity, lethality in the advanced setting and association with ultraviolet exposure early in life. Analysis of whole-genome sequence data identified PREX2 (phosphatidylinositol-3,4,5-trisphosphate-dependent Rac exchange factor 2)-a PTEN-interacting protein and negative regulator of PTEN in breast cancer--as a significantly mutated gene with a mutation frequency of approximately 14% in an independent extension cohort of 107 human melanomas. PREX2 mutations are biologically relevant, as ectopic expression of mutant PREX2 accelerated tumour formation of immortalized human melanocytes. Previous work suggested that PREX2 alterations may enrich for responses to immune checkpoint inhibitors (ICI), validation of function in melanoma is needed. Methods: Using 539-gene target-capture next generation sequencing, we analyzed the PREX2 mutation in 3547 tumor tissue or plasma ctDNA samples (including 122 melanoma) from different patients, and the public database of TACG was also compared. Data from Snyder-64 study (n = 64, anti- CTLA-4 therapy) was retrieved and analysed. In survival analysis, Kaplan-Meier curves were compared by log-rank test, and the hazard ratio (HR) was determined through a multivariable Cox regression model. Results: In clinical cohort, the frequency of PREX2 mutation in 3547 tumor tissue or plasma ctDNA samples from different patients was 5.94 % (211 in 3547). Meanwhile, the frequency of PREX2 mutation in TCGA cohort was 5.06 % (555 in 10953). In melanoma datebase, the frequency of PREX2 mutation in 122 melanoma tumor tissue or plasma ctDNA samples from different patients was 6.55 % (78 in 122). Meanwhile, the frequency of PREX2 mutation in melanoma in TCGA cohort was 25.56 % (113 in 422). We further analyzed Kaplan-Meier curves from Snyder-64 study (n = 64, anti- CTLA-4 therapy). In Snyder-64 study melanoma cohort, mutation of PREX2 was associated with higher neoantigen load (P = 0.02) and higher mutation count (P = 0.0027) in melanoma. PREX2 mutation was associated with prolonged overall survival (OS) trend compared with PREX2 wt in melanoma cohort (P = 0.09). Conclusions: In our study, the frequency of PREX2 mutation in pan cancers and melanoma was investigated in clinical and TCGA cohort, which might provide useful information to guide precision medicine. PREX2 mutation may serve as a novel predictor of response to anti-PD-1/PD-L1 treatment in melanoma via upregulating neoantigen load and mutation count.

Preliminary results of a phase II study of alrizomadlin (APG-115), a novel, small-molecule MDM2 inhibitor, in combination with pembrolizumab in patients (pts) with unresectable or metastatic melanoma or advanced solid tumors that have failed immuno-oncologic (I-O) drugs.

2506 Background: Alrizomadlin (APG-115) restores TP53 function, activating p53-mediated apoptosis in tumor cells with wild-type TP53 and/or MDM2 amplification. Alrizomadlin also functions as a host immunomodulator and hence may restore antitumor activity in pts with cancers failing PD-1/PD-L1 blockade. Methods: This US multicenter trial assessed alrizomadlin combined with pembrolizumab in pts with unresectable/metastatic melanoma or advanced solid tumors that had failed I-O drugs; or pts with malignant peripheral nerve sheath tumor (MPNST), liposarcoma, or ATM mutant solid tumors that had failed any standard therapy. Eligible pts had ECOG performance status of 0-2 and no CNS metastases. The phase II study cohorts included pts with melanoma, NSCLC, solid tumor with ATM mutation, well-differentiated/dedifferentiated liposarcoma, urothelial carcinoma, and MPNST. Alrizomadlin was administered orally at 150 mg once every other day for 2 consecutive weeks with 1 week off and pembrolizumab at 200 mg via IV infusion for 30 minutes on Day 1 of a 21-day cycle. Results: As of December 25, 2020, 84 pts had been treated in 6 cohorts: melanoma (n = 26), NSCLC (n = 23), ATM mutation (n = 9), liposarcoma (n = 14), urothelial (n = 9), and MPNST (n = 3). In the PD-1/PD-L1 inhibitor-failed melanoma cohort, there was 1 confirmed partial response (PR) out of 5 pts with uveal melanoma, 2 PR (1 confirmed and 1 unconfirmed) of 5 pts with mucosal melanoma, and 1 confirmed PR of 11 pts with cutaneous melanoma. ORR in the melanoma cohort was 17.4% (4/23 evaluable pts), and the disease control rate was 60.9% (14/23). In the MPNST cohort, 1 of 3 pts had an unconfirmed ongoing PR. In I-O drug-failed NSCLC (n = 14 evaluable) and urothelial (n = 5 evaluable) cohorts, each reported 1 confirmed PR. Common treatment (alrizomadlin or pembrolizumab)-related adverse events (TRAEs) (≥ 10%) were nausea (63.1%), thrombocytopenia (36.9%), vomiting (33.3%), fatigue (31.0%), decreased appetite (27.4%), diarrhea (21.4%), neutropenia (15.4%), and anemia (11.9%). Grade ≥ 3 TRAEs (≥ 5%) included thrombocytopenia (20.2%), neutropenia (14.2%), and anemia (8.3%). Eleven pts discontinued treatment due to AEs: 5 were treatment related, including 2 grade 4 thrombocytopenia, and 1 each of grade 2 vomiting, grade 2 fatigue, and grade 2 posterior reversible encephalopathy syndrome (PRES). Three treatment-related SAEs were PRES, pyrexia, and asthenia. Conclusions: Alrizomadlin combined with pembrolizumab is well tolerated and may restore antitumor effects in pts with cancer resistant to or intolerant of I-O drugs, as suggested by preliminary antitumor activities in multiple tumor types. Internal study identifiers: APG-115-US-002; Keynote MK-3475-B66. Clinical trial information: NCT03611868.

Comparing the clinical efficacies of anti-PD-1 antibody monotherapy and anti-PD-1 and anti-CTLA-4 combination therapy as first-line immunotherapy in Japanese advanced acral melanoma: A retrospective, multicenter study (JAMP-neo study).

9542 Background: Anti-PD-1 antibody monotherapy (PD1) has been commonly used for patients with advanced acral melanoma (AM). However, recent studies have demonstrated the limited clinical efficacy of PD1 in AM compared to non-acral cutaneous melanoma, particularly in nail apparatus melanoma. Although advanced AM patients are strong candidates for first-line anti-PD-1 and anti-CTLA-4 combination therapy (PD1+CTLA4), data on the clinical efficacy of PD1+CTLA4 in AM are lacking. Thus, we aimed to compare the clinical efficacies of PD1+CTLA4 and PD1 in Japanese advanced AM patients. Methods: We retrospectively reviewed the clinical records of advanced AM patients treated with PD1+CTLA4 or PD1 as first-line immunotherapy at 23 Japanese institutions. Clinical response was assessed using the Response Evaluation Criteria in Solid Tumors (RECIST) criteria. Survival was estimated using Kaplan-Meier analysis. Toxicity was assessed according to CTCAE 4.0. Results: A total of 192 patients (median age, 72 years) with advanced AM (palm and sole melanoma, 135; nail apparatus melanoma, 57) were included in the study. PD1+CTLA4 and PD1 were used as first-line immunotherapy in 39 and 153 patients, respectively. The baseline demographics and characteristics were similar between the PD1+CTLA4 and PD1 groups, except for age (median age 67.3 vs. 73.2; P = 0.005). The objective response rate (ORR) in PD1+CTLA4 was significantly higher than that of the PD1 group (38.5% vs. 16.3%; P = 0.047). The median progression-free survival (PFS) and overall survival (OS) in the PD1+CTLA4 group tended to be longer than those of the PD1 group, but the differences were not significant (median PFS 7.3 months vs. 4.5 months; P = 0.19, median OS 43.6 months vs. 18.2 months; P = 0.19). In the subgroup analysis of the palm and sole melanoma cohorts, no significant differences in ORR, PFS, and OS were observed between the PD1+CTLA4 and PD1 groups (ORR 31% vs. 20.8%; P = 0.67, median PFS 5.3 months vs. 5.9 months; P = 0.87, median OS not reached vs. 22.3 months; P = 0.66). Meanwhile, the nail apparatus melanoma cohort in the PD1+CTLA4 group exhibited significantly higher ORR, and longer PFS and OS than the PD1 group (ORR 60% vs 6.1%; P < 0.001; median PFS 19.6 months vs 3.8 months; P = 0.008, median OS 43.6 months vs 13.5 months; P = 0.049). Due to immune-related adverse events in all cohorts, the treatment cessation rate was higher in the PD1+CTLA4 group than the PD1 group (59% vs. 11.8%). Conclusions: PD1+CTLA4 was clinically more efficacious than PD 1 in advanced AM patients. Notably, advanced nail apparatus melanoma patients were strong candidates for first-line PD1+CTLA4.

RECQL5 mutations as a potential efficacious predictor of immunotherapy in melanoma patients.

e21547 Background: Gene mutations in DNA damage repair (DDR) pathway were reported to affect the clinical response to immune checkpoint inhibitors (ICIs) by driving mutagenicity. Previous studies showed that RECQL5 is involved in RAD51-mediated strand invasion for homologous recombination DNA damage repair (HR-DDR). RECQL5 encoding RecQ protein-like 5 (RECQL5) is a member of RecQ helicase family and was discovered to play a tumor-suppressive or oncogenic role in various cancers. However, the association between RECQL5 mutation and ICI efficacy has not been revealed. Methods: Data of nine publicly independent cohorts of NSCLC, melanoma, and pan-cancer were retrieved (Rizvi, MSKCC, OAK/POPLAR, Van Allen, Hugo, Synder, Miao and Samstein cohorts) to investigate the correlation between RECQL5 mutations and clinical events including overall survival (OS), progression-free survival (PFS), objective response rate (ORR), and clinical benefit rate (CBR). Wilcoxon test was used for comparing tumor mutational burden (TMB) between RECQL5-mutated patients and their wild-type counterparts. In addition, the correlation between infiltration of immune cells and RECQL5 mutation status was also analyzed by QUANTISEO using data of SKCM cohort (n=466) from TCGA database. Statistical significance was set at P = 0.05. Results: RECQL5 mutations were most commonly seen in melanoma patients and the detection rate was 4%-8% in melanoma patients from cohort Van Allen, Hugo, Synder, and Miao. RECQL5 mutation was not detected in other cancers except for one lung cancer case. In the three melanoma cohorts (Van Allen, Synder, Miao) with OS data available, the OS of the RECQL5-mutated patients was 2 to 3 times longer than that of the RECQL5-wt patients. In Synder cohort, the difference in OS between these two subsets was statistically significant (53.9 months vs 25.0 months, P = 0.045). In addition, the occurrence of RECQL5 mutations was correlated with higher CBR both in Miao ( P = 0.017) and Synder cohorts ( P = 0.011). No difference was observed in the PFS or ORR between these two subsets. Notably, RECQL5 mutations were associated with higher TMB levels both in Miao (32.6 mut/Mb vs 7.9 mut/Mb, P = 0.016) and Synder cohorts (1124 mut/Mb vs 358 mut/Mb, P = 0.033). Moreover, RECQL5 mutations were found to be correlated with increased infiltration of CD4+ T cells (no-regulatory) ( P = 0.037), B cells ( P = 0.13) and decreased infiltration of regulatory CD4+ T cells ( P = 0.02) in RECQL5-mutated tumors over RECQL5-wt tumors. Conclusions: RECQL5 mutations can serve as a potential predictor for a durable response to ICIs in melanoma. Moreover, the occurrence of RECQL5 mutations was correlated with higher TMB level as well as infiltration of immune cells, indicating the underlying mechanism of its predictive effect.

Increased risk of immune-related hepatitis among adolescent and young adults (AYAs) with melanoma during immunotherapy with checkpoint inhibitors (ICIs).

9584 Background: Melanoma is the second most common malignancy affecting AYA patients after lymphoma. Nevertheless, AYA melanoma does constitute a minority of all melanoma cases. Additionally, the AYA population is not well represented in prospective clinical trials, including immunotherapy trials. While previous research has demonstrated the efficacy of ICIs across age groups, it remains unclear if toxicity profiles will be similar. In the general population, age-related changes in the immune milieu result in differential incidences of autoimmune diseases by age. This study aims to compare the toxicity profile between a cohort of AYA melanoma versus elderly melanoma patients receiving ICI therapy. Methods: In this single NCCN institutional study, electronic medical records of melanoma patients treated with ICIs between 01/2007-01/2019 were reviewed. Subjects receiving concurrent investigational agents or chemotherapy were excluded. The AYA cohort included those aged 15-40 years. The elderly cohort included those aged ≥65 years. Adverse events were coded according to CTC-AE version 5.0. Multivariable logistic regression analyses were performed. Results: Analyses included 184 treatment courses. In the AYA cohort (N = 57), median age at ICI initiation was 28.8 years (range: 17.9-39.3). In the Elderly cohort (N = 127), median age at ICI initiation was 72.3 years. More AYA patients (28.1% AYA vs. 7.9% Elderly) received ICI combination regimens. The most common adverse events amongst both cohorts were transaminitis (23.4%), rashes (49.5%), and diarrhea/colitis (20%). Incidences of pneumonitis, colitis, hypothyroidism, and hypophysitis did not differ significantly between cohorts. However, the AYA cohort experienced a higher incidence of transaminitis (38.6% AYA vs. 16.5% Elderly, p =0.001 ) and increased occurrence of treatment related hospitalization (26.3% AYA vs. 7.1% Elderly, p <0.001 ). Moreover, a higher proportion of severe grade ≥3 transaminitis occurred in the AYA group (27.3% AYA vs. 9.5% Elderly, p =0.004). While occurrence of transaminitis was significantly associated with combination ICIs, the association between AYA status and transaminitis remained significant after adjusting for ICI regimen (OR 2.75, 95% CI: 1.3-5.8). There was a trend toward shorter time to transaminitis onset among the AYA than Elderly cohort (median 53.0 vs. 74.5 days [non-parametric p= 0.28]). To date, median survival has not been reached in both groups ( p= 0.09). Conclusions: In this large cohort of AYA melanoma patients treated with ICI, we found a significantly higher incidence of immune-related transaminitis than in the Elderly cohort. Other immune-related AEs were comparable between cohorts. This finding was independent of ICI regimen. Further investigation will be needed to understand these differences between the AYA and Elderly cohorts.

Association of LRP1B mutants with immune biomarkers in Chinese non-small cell lung cancer patients.

e21060 Background: LRP1B (low-density lipoprotein receptor-related protein 1B) is frequently mutated in non-small cell lung cancer (NSCLC). Previous studies showed LRP1B mutations were associated with prolonged survival in melanoma and NSCLC immunotherapy cohort. Higher tumor mutation burden was found in LRP1B mutated patients, suggesting potential benefit of immunotherapy. Herein, we investigate the relationship of LRP1B and immunotherapy biomarker in lager cohort of Chinese and Western NSCLC patients. Methods: Next-generation sequencing data and clinical data were collected from 1053 TCGA NSCLC patients (Western cohort). A 539-gene panel targeted sequencing assay was performed on FFPE tumor samples from 1056 Chinese pan-cancer patients (Chinese cohort). Both LRP1B mutation ratio and TMB were calculated on the two cohorts following the same criteria. TMB-H was defined as the top quartile of all TMB values. Results: In total, 208 (20%) of the 1056 Chinese patients and 385 (37%) of the 1053 Western patients had at least one mutation of LRP1B genes (LRP1B mutant group). The frequency of LRP1B mutation between Western cohort and Chinese cohort had significant difference (20% vs. 37%, p＜0.001). In both cohorts, TMB was higher in the LRP1B mutant group compared to non-LRP1B mutant group. In Chinese cohort, PD-L1 positive was not associated with LRP1B mutation. Patients with LRP1B mutation were associated with prolonged survival in Western immunotherapy cohort. Conclusions: Our study provided a landscape of LRP1B mutations in a much larger Chinese NSCLC group, which could be a valuable complement to TCGA dataset and previous study. Results of our study was consistent with previous studies. Both in Chinese and Western cohorts, the higher TMB in LRP1B mutant patients suggested potential efficacy from immunotherapy of LRP1B mutant group. This result and the potential predictive value of LRP1B in immunotherapy should be validation in a larger Chinese LRP1B mutant cohort in the further.

Identification of a microbiome signature predicting immune checkpoint inhibitor outcomes across multiple cancer types in the MITRE study.

TPS2665 Background: The gut microbiome is implicated as a biomarker of response to immune checkpoint inhibitors (ICIs), based on preclinical mouse models and preliminary observations in limited patient series. Furthermore, early reports suggest faecal microbial transfer may have therapeutic potential, converting ICI non-responders to responders. So far, identification of specific responsible bacterial taxa has been inconsistent between published studies, which limits future application. By culturing and metagenomic sequencing of stool sample bacteria, our group has identified a unique microbiome signature, which appears to be predictive of response to ICIs across all key published series as well as our own melanoma patient series (Robinson M et al, J Immunother Cancer 2020;8(suppl 3):A404). Because the patient numbers in all published series remain low, we are now further exploring and validating this microbiome signature in a larger scale study across several different cancer types. Methods: MITRE (Microbiome Immunotherapy Toxicity and Response Evaluation) is a UK NIHR portfolio multi-centre prospective study funded jointly by Cancer Research UK and Microbiotica (NCT04107168). Up to 1800 patients receiving ICIs will be recruited over a 5-year period. In the first stage, 300 patients with advanced melanoma (cohort 1: anti-PD1 monotherapy, cohort 2: anti-PD1+anti-CTLA-4 combination), renal cancer (cohort 3: anti-PD(L)1+kinase inhibitor, cohort 4: anti-PD1+anti-CTLA-4 combination) and non-small cell lung cancer (cohort 5: anti-PD(L)1 monotherapy, cohort 6: anti-PD(L)1+chemotherapy+anti-angiogenic) are being recruited, 50 patients to each cohort. A cohort-specific, simulation-based power calculation will then be performed, guiding subsequent recruitment. Stool and blood are collected prior to treatment, at 3, 6 and 12 months, or disease progression (whichever is sooner), as well as after any grade >3 immune-related adverse events. Patients collect and freeze their own stool samples which are cultured and subjected to shotgun metagenomic sequencing. Plasma, whole blood, buffy coat, RNA and PBMCs are being stored, for correlative studies. Any tumour, or organ biopsies, taken prior to and during treatment are also being collected. Clinical data collection includes treatment, disease response (using RECIST criteria) and toxicity. The primary outcome measure is 1 year progression-free survival. Patients are also asked to invite a household member to be part of the study control group. Recruitment started in July 2020. The Covid-19 pandemic hindered recruitment last year, but the protocol was amended to incorporate a Covid-19 substudy (to document testing, infection and vaccination) and adapt processes for remote trial delivery as much as possible. As of February 2021, 7 sites have opened, 17 patients and 5 household controls have been recruited. Clinical trial information: NCT04107168.

ARTISTRY-1: Nemvaleukin alfa monotherapy and in combination with pembrolizumab in patients (pts) with advanced solid tumors.

2513 Background: Nemvaleukin alfa (nemvaleukin, ALKS 4230) is a novel, engineered cytokine that selectively binds the intermediate-affinity interleukin-2 (IL-2) receptor complex to preferentially activate CD8+ T cells and natural killer cells with minimal expansion of regulatory T cells, designed to leverage antitumor effects of the IL-2 pathwaywhile mitigating potential toxicity that would limit use. Methods: ARTISTRY-1 (NCT02799095) is a phase 1/2 study. Parts A (dose escalation 0.1-10 µg/kg) and B (6 µg/kg [recommended phase 2 dose]) are monotherapy; pts receive intravenous nemvaleukin for 5 days every 14 or 21 days. In Part C, pts receive nemvaleukin (3 or 6 µg/kg) every 21 days in combination with pembrolizumab (200 mg on day 1). We present safety and antitumor activity (RECIST v1.1, iRECIST) data as of 12/02/2020. Results: In Part A, 39 pts received nemvaleukin. No dose-limiting toxicities were observed; maximum tolerated dose was not reached. Part B enrolled immune checkpoint inhibitor–pretreated pts into melanoma or renal cell carcinoma (RCC) cohorts. 18 pts with melanoma enrolled; 10 were evaluable, 2 (both with metastatic mucosal melanoma) achieved a partial response (PR; 1 unconfirmed). 24 pts with RCC enrolled; 1 of 16 evaluable pts achieved a PR (awaiting confirmation). 12 pts in each cohort continue on study. In Parts A and B, treatment-related adverse events in ≥40% included chills (74.4% and 52.4%, respectively) and pyrexia (74.4% and 47.6%, respectively). In Part C (83 evaluable pts), 12 objective responses (OR) were observed; an additional 5 pts had stable disease (SD) >6 months (1 pt with breast cancer, 2 with ovarian cancer, and 2 with non-small-cell lung cancer). Nemvaleukin did not demonstrate any additive toxicity to that already established with pembrolizumab alone. OR data are summarized in the table. Conclusions: Nemvaleukin was generally well tolerated and demonstrated antitumor activity as monotherapy and in combination with pembrolizumab. Pharmacodynamic studies to identify biomarkers are ongoing. Future research of monotherapy and combination therapy with nemvaleukin is warranted. Clinical trial information: NCT02799095. [Table: see text]

Clinicopathologic and molecular characterization of melanomas mutated for CTNNB1 and MAPK.

Wnt/β-catenin signaling plays crucial roles in melanocyte biology and may be implicated in melanoma progression. In this study, we retrospectively examined a real-life cohort of melanomas mutated for β-catenin (CTNNB1), in association or not with a MAPK mutation (of BRAF or NRAS), and analyzed their clinical, histopathological, and molecular characteristics. Our results indicate that, regardless of the presence of a concurrent MAPK mutation, CTNNB1mut cutaneous primary melanomas display more proliferative hallmarks (increased Breslow thickness, mitotic index, and ulceration) than their CTNNB1 wild-type counterparts. Accordingly, they often progress to the metastatic stage. Furthermore, concurrent CTNNB1 and MAPK mutations do not necessarily confer a deep penetrating nevi phenotype. Altogether, this study provides evidence that CTNNB1 mutations in melanomas are associated with specific clinical and pathological features.

Molecular markers of response to anti-PD1 therapy in advanced hepatocellular carcinoma.

4100 Background: Checkpoint inhibition with anti-PD1 is able to elicit objective response rates (ORR) of ̃ 20% in patients with advanced hepatocellular carcinoma (aHCC) but molecular biomarkers predicting response remain unknown. Here, we define biomarkers of response and primary resistance to anti-PD1 in aHCC by analyzing molecular features prior to systemic therapy. Methods: Through an international consortium of 13 referral centers, we gathered 111 fresh and archived tumor samples from patients with advanced HCC treated with single agent anti- PD1 therapy. Genomic analysis was performed with whole genome expression arrays, CTNNB1 exon 3 mutation assessment and histological evaluation. Results: Overall, we performed transcriptomic analysis in 83 patients, 28 of which were treated in first-line (ORR: 42.9%) while the remaining 55 patients were treated either in 2nd (41 patients, ORR 29.3%) or 3rd line (14 patients, ORR 7.1%) after prior therapy with tyrosine- kinase inhibitors (TKI) sorafenib or lenvatinib. In patients treated in frontline, response was associated with a significant upregulation in Interferon-γ signaling (IFNγ) and genesets relatedto the antigen presentation machinery (FDR < 0.05). Through differential expression analysis we defined an 11-gene signature that was significantly associated with both major pathways (FDR < 0.01) and was capable of predicting OR as well as progression-free- (PFS) and overall survival (OS) in patients with aHCC. The signature was validated in three independent cohorts of melanoma, lung cancer, and head and neck squamous cell cancer patients were high expression was associated with a significant increase in ORR and longer PFS. In HCC, high expression of the signature was associated with a distinct profile in the immune infiltrate, where an increase in M1 macrophages (p = 0.003), CD4 memory T cell (p < 0.01) and CD4 naïve T cell-infiltration (p = 0.026) was observed. Conversely, low expression of the signature was associated with a marked upregulation of regulatory T cells (p < 0.001). No association was found, however, between either the overall immune infiltrate or CTNNB1 mutations and response. In patients that were treated with TKIs in frontline before receiving subsequent anti-PD1 therapy, the signature was no longer able to predict either OR or PFS/OS, suggesting that TKIs may reshape the microenvironment in a way that renders previously inflamed tumors no longer amenable to anti-PD1. Conclusions: Here, we define an 11-gene signature of response to anti-PD1 in first line aHCC. The signature was validated in patients with other solid cancer types, where it retained its predictive ability. Of note, the signature was not able to identify responders among HCC patients that were treated with TKIs prior to anti-PD1 therapy. The molecular changes induced by different treatment lines would, thus, require fresh biopsies prior to anti-PD1to enable biomarker-driven treatment.

FAT4 mutation serve as a novel predictor of response to anti-PD-1/PD-L1 treatment in melanoma.

e21553 Background: FAT4 functions as a tumor suppressor, and previous findings have demonstrated that FAT4 can inhibit the epithelial-to-mesenchymal transition (EMT) and the proliferation of gastric cancer cells. FAT4 is involved in the maintenance of PCP and inhibition of cell proliferation. FAT4 mRNA is repressed in breast cancer and lung cancer due to promoter hypermethylation. FAT4 gene is recurrently mutated in several types. Previous work suggested that FAT4 alterations may enrich for responses to immune checkpoint inhibitors (ICI), validation of function in melanoma is needed. Methods: Using 539-gene target-capture next generation sequencing, we analyzed the FAT4 mutation in 3547 tumor tissue or plasma ctDNA samples (including 122 melanoma) from different patients, and the public database of TACG was also compared. Data from Miao-249 study (n = 151, anti-PD-(L)1/CTLA-4 mono/ combined therapy) was retrieved and analysed. In survival analysis, Kaplan-Meier curves were compared by log-rank test, and the hazard ratio (HR) was determined through a multivariable Cox regression model. Results: In clinical cohort, the frequency of FAT4 mutation in 3547 tumor tissue or plasma ctDNA samples from different patients was 8.11 % (288 in 3547). Meanwhile, the frequency of FAT4 mutation in TCGA cohort was 10.08 % (1105 in 10953). In melanoma datebase, the frequency of FAT4 mutation in 122 melanoma tumor tissue or plasma ctDNA samples from different patients was 5.73 % (7 in 122). Meanwhile, the frequency of FAT4 mutation in melanoma in TCGA cohort was 38.2 % (169 in 422) We further analyzed Kaplan-Meier curves from Miao-249 study (n = 151, anti-PD-(L)1/CTLA-4 mono/ combined therapy). In Miao-249 melanoma cohort, mutation of FAT4 was associated with higher TMB (P = 0.032) and higher mutation count (P = 0.003) in melanoma. FAT4 mutation was associated with prolonged overall survival (OS) compared with FAT4 wt in melanoma (P = 0.0478). Conclusions: In our study, the frequency of FAT4 mutation in pan cancers and melanoma was investigated in clinical and TCGA cohort, which might provide useful information to guide precision medicine. FAT4 mutation may serve as a novel predictor of response to anti-PD-1/PD-L1 treatment in melanoma via upregulating TMB and mutation count.

Using precision microbiome profiling to develop a biomarker for immune checkpoint inhibitor response and a novel therapeutic.

e21546 Background: Four independent groups have demonstrated that the pre-treatment gut microbiome of cancer patients impacts the subsequent response to Immune Checkpoint Inhibitor (ICIs) therapy [1-4]. However, the patient’s outcome was linked to different bacteria in each study, which has limited the development of drug response biomarkers and clinic-first design of novel microbiome-based therapeutics. Methods: The Cambridge (UK) MELRESIST study includes a cohort of advanced melanoma patients receiving approved ICIs. Pretreatment stool samples from MELRESIST were analysed by Microbiotica using shotgun metagenomic sequencing. Microbiotica’s platform comprises the world’s leading Reference Genome Database to give the most comprehensive and precise mapping of the gut microbiome. Results: MELRESIST samples showed an overall difference in the microbiome composition between advanced melanoma patients and healthy donors, but not between patients who did or did not respond to ICIs. However, we did identify a discrete microbiome signature that differentiated responders and non-responders with an accuracy of 93%. We extended this signature by reanalysing three published melanoma cohorts [1-3] using the Microbiotica platform, and a propriety bioinformatic model. The resultant bacterial signature was very accurate at predicting response in all 4 published studies combined (91%), and each cohort individually (82-100%). We validated the model using independent validation cohorts and the signature using lung and renal cancer studies [4]. At the core of our microbiome signature was 9 bacteria most significantly associated with ICI efficacy. All 9 were overrepresented in patients who responded to immunotherapy suggesting high abundance of these bacteria is a central driver of ICI response. A consortium comprised of all 9 strains had very potent anti-tumor efficacy in a cancer syngeneic mouse model. The bacteria also demonstrate multiple interactions with primary human immune cells in vitro leading to dendritic cells activation, Cytotoxic T lymphocyte activation and tumor cell killing. These validate the potential of this consortium as a novel therapy for use in combination with ICIs. Conclusions: We have identified a unique microbiome signature predictive of ICI response in 4 independent melanoma cancer cohorts. This removes a major challenge to the field, and could represent a new highly accurate biomarker with clinical application. Nine core bacteria appear to be driving response, and demonstrate anti-tumor activity in vivo and in vitro. This consortium holds great potential as a co-therapy with ICIs.

The predictive value of MAP2K1/2 mutations for efficiency of immunotherapy in melanoma.

e21587 Background: Immunotherapies targeting immune checkpoint receptors have become the cornerstone of systemic treatment options for malignant melanoma. The response to these immunotherapies may correlate with driver mutations. MAP2K1/2 genes are mutated in approximately 10% of melanomas, however, the impact of MAP2K1/2 gene alterations on the efficiency of immunotherapy has not been clarified. Methods: Six metastatic melanoma clinical cohorts treated with ICIs were included to investigate the association between clinical efficacy of immunotherapy and MAP2K1/2 mutations. Survival analyses were conducted in cohorts receiving two kinds of ICB agents, namely anti-CTLA-4 or anti-PD-1. RNA expression profiling from these cohorts and from the TCGA melanoma cohort were used to explore the potential mechanism related to immune activation. Results: In an independent anti-CTLA-4-treated cohort (n = 110), we found that MAP2K1/2 mutations are predictive of high objective response rate (17.6% vs 1.3%, p = 0.0185) and long progression-free survival [median OS, 49.2 months vs 8.3 months; hazard ratio (HR) = 0.37; 95% CI, 0.15–0.91; p = 0.0307] and overall survival (median PFS, 19.4 months vs 2.8 months; HR = 0.2; 95% CI, 0.05–0.83; p = 0.0262). This predictive value was further validated in a pooled anti-CTLA-4-treated cohort (n = 235) in terms of overall survival (median OS, 49.3 months vs 22.0 months; HR = 0.44; 95% CI, 0.22–0.91; p = 0.0255). However, no correlation between MAP2K1/2 mutations and overall survival was observed in the anti-PD-1-treated cohort (n = 285). Subgroup Cox regression analysis indicated that MAP2K-mutated patients receive less benefit from the anti-PD-1 monotherapy than from the anti-CTLA-4 treatment (median OS, 27.0 months vs 49.3 months; HR = 3.26; 95% CI, 1.18–9.02; p = 0.0225), which was contrary to the result obtained for the total population. Furthermore, transcriptome profiling analysis revealed that MAP2K-mutated tumors are enriched in CD8+ T cells, B cells, and neutrophil cells and also express high levels of CD33 and IL10, which might be the underlying mechanism for melanoma patients with MAP2K1/2-mutated benefit more from anti-CTLA-4 treatment. Conclusions: We identified mutations in MAP2K1/2 genes as the independent predictive factors for anti-CTLA-4 therapy in melanoma patients and found that anti-CTLA-4 treatment in patient harbouring MAP2K1/2 mutations might be more effective than the anti-PD-1 therapy.