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Although melanoma is amenable to early detection, there has been no decline in the mortality rate of this disease and the prognosis of patients with high-risk primary melanoma or with macroscopic nodal involvement remains poor. The best option for patients with higher-risk melanoma is to receive effective adjuvant therapy in order to reduce their chances of recurrence. Multiple systemic therapeutic agents have been tested as adjuvant therapy for melanoma with durable benefits seen only with interferon- to date. More recently ipilimumab at the high dose of 10 mg/kg has shown a significant improvement in terms of Relapse free survival and Overall survival for stage III melanoma patients but at a significant cost in terms of immune-related toxicities. More recently, novel treatment options have emerged. The results from the latest trials with immunotherapy (PD-1 inhibitors) and molecular targeted therapy (BRAF inhibitor + MEK inhibitor) have revolutionized the management of adjuvant treatment for melanoma. As the results from these trials will mature in the next years, a change in the landscape of adjuvant treatment for melanoma is expected, resulting in new challenges in treatment decisions such as optimizing patients' selection through predictive and prognostic biomarkers, and management of treatment related adverse events, in particular immune related toxicities. [ABSTRACT FROM AUTHOR]

A few months ago, results from two randomised phase III trials of total neoadjuvant therapy (TNT) in locally advanced rectal cancer were presented (RAPIDO and PRODIGE 23), consistently showing better short- and long-term outcomes with TNT as compared with standard neoadjuvant long-course chemoradiotherapy (CRT) or short-course radiotherapy (SCRT). These results represent corroborating evidence in support of a practice that many centres had already implemented based on promising preliminary data. Also, they provide new, high-level evidence to endorse TNT as a new management option in the treatment algorithm of stage II-III rectal cancer in those centres where CRT and SCRT have long remained the only accepted standard neoadjuvant treatments. Having two consistently positive trials is certainly reassuring regarding the potential of TNT as a general treatment approach. Nevertheless, substantial differences between these trials pose important challenges in relation to the generalisability and applicability of their results, and translation of the same into practical clinical recommendations. In this article, we address a number of key questions that the RAPIDO and PRODIGE 23 trials have raised among the broad community of gastrointestinal oncologists, proposing an interpretation of the data that may help the decision making, and highlighting grey areas that warrant further investigation. [ABSTRACT FROM AUTHOR]

Epidermal growth factor receptor (EGFR) inhibitors are valuable therapeutics in metastatic colorectal cancer (mCRC). Anti-EGFR monoclonal antibodies (MoAbs), such as cetuximab or panitumumab, in combination with chemotherapy are effective treatment options for patients with RAS and BRAF wild-type mCRC. Nevertheless, several issues are still open concerning the optimal use of anti-EGFR drugs in the continuum of care of mCRC. Novel approaches for increasing the efficacy of anti-EGFR therapies include better molecular selection of EGFR-dependent mCRC, intensification of chemotherapy, combination of anti-EGFR MoAbs and immune checkpoint inhibitors, and reintroduction of EGFR blockade or 'rechallenge' in selected patients who have previously responded to anti-EGFR MoAb therapy. An extensive translational research program was conducted in the Cetuximab After Progression in KRAS wIld-type colorectal cancer patients-Gruppo Oncologico dell' Italia Meridionale (CAPRI-GOIM) study with the aims of determining which subgroups of patients could benefit from the continuous inhibition of EGFR, from evaluating the role of liquid biopsy-based and its concordance with tissue-based molecular testing, and from investigating novel potential mechanisms of resistance to anti-EGFR therapies. In this review, we summarize the translational and clinical findings of the CAPRI-GOIM program in the context of the current knowledge of therapeutic strategies and of ongoing research on more appropriate uses of anti-EGFR therapies in RAS and BRAF wild-type mCRC patients. • The epidermal growth factor (EGFR) is a therapeutic option for patients with all RAS WT metastatic colorectal cancer (mCRC). • A better knowledge of the mechanism of primary or acquired resistance to EGFR-therapies can improve patient's selection. • Despite disease progression a subset of mCRC are still sensitive to EGFR inhibition. • Rechallenge strategies with anti-EGFR might represent a promising therapeutic option. [ABSTRACT FROM AUTHOR]

Background NTRK1 , NTRK2 and NTRK3 fusions are present in a plethora of malignancies across different histologies. These fusions represent the most frequent mechanism of oncogenic activation of these receptor tyrosine kinases, and biomarkers for the use of TRK small molecule inhibitors. Given the varying frequency of NTRK1/2/3 fusions, crucial to the administration of NTRK inhibitors is the development of optimal approaches for the detection of human cancers harbouring activating NTRK1/2/3 fusion genes. Materials and methods Experts from several Institutions were recruited by the European Society for Medical Oncology (ESMO) Translational Research and Precision Medicine Working Group (TR and PM WG) to review the available methods for the detection of NTRK gene fusions, their potential applications, and strategies for the implementation of a rational approach for the detection of NTRK1/2/3 fusion genes in human malignancies. A consensus on the most reasonable strategy to adopt when screening for NTRK fusions in oncologic patients was sought, and further reviewed and approved by the ESMO TR and PM WG and the ESMO leadership. Results The main techniques employed for NTRK fusion gene detection include immunohistochemistry, fluorescence in situ hybridization (FISH), RT-PCR, and both RNA-based and DNA-based next generation sequencing (NGS). Each technique has advantages and limitations, and the choice of assays for screening and final diagnosis should also take into account the resources and clinical context. Conclusion In tumours where NTRK fusions are highly recurrent, FISH, RT-PCR or RNA-based sequencing panels can be used as confirmatory techniques, whereas in the scenario of testing an unselected population where NTRK1/2/3 fusions are uncommon, either front-line sequencing (preferentially RNA-sequencing) or screening by immunohistochemistry followed by sequencing of positive cases should be pursued. [ABSTRACT FROM AUTHOR]

Background: Cetuximab plus chemotherapy is a first-line treatment option in metastatic KRAS and NRAS wild-type colorectal cancer (CRC) patients. No data are currently available on continuing anti-epidermal growth factor receptor (EGFR) therapy beyond progression. Patients and methods: We did this open-label, 1:1 randomized phase II trial at 25 hospitals in Italy to evaluate the efficacy of cetuximab plus 5-fluorouracil, folinic acid and oxaliplatin (FOLFOX) as second-line treatment of KRAS exon 2 wild-type metastatic CRC patients treated in first line with 5-fluorouracil, folinic acid and irinotecan (FOLFIRI) plus cetuximab. Patients received FOLFOX plus cetuximab (arm A) or FOLFOX (arm B). Primary end point was progressionfree survival (PFS). Tumour tissues were assessed by next-generation sequencing (NGS). This report is the final analysis. Results: Between 1 February 2010 and 28 September 2014, 153 patients were randomized (74 in arm A and 79 in arm B). Median PFS was 6.4 [95% confidence interval (CI) 4.7-8.0] versus 4.5 months (95% CI 3.3-5.7); [hazard ratio (HR), 0.81; 95% CI 0.58-1.12; P = 0.19], respectively. NGS was performed in 117/153 (76.5%) cases; 66/117 patients (34 in arm A and 32 in arm B) had KRAS, NRAS, BRAF and PIK3CA wild-type tumours. For these patients, PFS was longer in the FOLFOX plus cetuximab arm [median 6.9 (95% CI 5.5-8.2) versus 5.3 months (95% CI 3.7-6.9); HR, 0.56 (95% CI 0.33-0.94); P = 0.025]. There was a trend in better overall survival: median 23.7 [(95% CI 19.4-28.0) versus 19.8 months (95% CI 14.9-24.7); HR, 0.57 (95% CI 0.32-1.02); P = 0.056]. Conclusions: Continuing cetuximab treatment in combination with chemotherapy is of potential therapeutic efficacy in molecularly selected patients and should be validated in randomized phase III trials. [ABSTRACT FROM AUTHOR]

Background: Evidence suggests that metastatic colorectal carcinoma (mCRC) has a high level of intratumor heterogeneity. We carried out a quantitative assessment of tumor heterogeneity for KRAS, NRAS, BRAF and PIK3CA mutations, in order to assess potential clinical implications. Patients and methods: Tumor samples (n = 182) from the CAPRI-GOIM trial of first-line cetuximab + FOLFIRI in KRAS exon-2 wild-type mCRC patients were assessed by next-generation sequencing that allows quantitative assessment of mutant genes. Mutant allelic frequency was normalized for the neoplastic cell content and, assuming that somatic mutations usually affect one allele, the Heterogeneity Score (HS) was calculated by multiplying by 2 the frequency of mutant alleles in neoplastic cells. Therefore, HS virtually corresponds to the fraction of neoplastic cells carrying a specific mutation. Results: The KRAS HS ranged between 12 and 260 with mean value of 87.1 and median value of 84.4, suggesting that in most CRC, the majority of neoplastic cells carry mutant KRAS. Similar findings were observed for NRAS (HS range 35.5-146.7; mean 102.8; median 117.1). In contrast, in BRAF (HS range 17.1-120; mean 54.8; median 54.3) and PIK3CA (HS range 14.3-120; mean 59.5; median 47.3) mutant cases, only a fraction of neoplastic cells seem to carry the mutant allele. The response rate was 70% in KRAS mutant patients with an HS <33 (low KRAS; n = 10) and 45.7% in KRAS HS >33 patients (high KRAS; n = 35); median progression-free survival were 7.97 and 8.37 months, respectively. Low-KRAS tumors had a higher frequency of additional mutations in PIK3CA when compared with high-KRAS (6/10 versus 8/35). Conclusions: KRAS and NRAS mutations are usually present in the majority of neoplastic cells, whereas BRAF and PIK3CA mutations often affect a limited fraction of transformed cells. Resistance to cetuximab in low-KRAS patients might be driven by the complex mutational profile rather than KRAS mutation load. [ABSTRACT FROM AUTHOR]

In this study, we developed and validated a next-generation sequencing gene panel covering 22 different genes that have been fully sequenced in multiple exons to cover >500 potential mutation sites. The results show that the technique is feasible, reproducible and could be done with a high efficiency in FFPE archival material (100% of success in the analysis in the 182 cases that were available).Background Treatment with antiepidermal growth factor receptor (anti-EGFR) monoclonal antibodies has been restricted to metastatic colorectal cancer (mCRC) patients with RAS wild-type tumors. Next-generation sequencing (NGS) allows the assessment in a single analysis of a large number of gene alterations and might provide important predictive and prognostic information. Patients and methods In the CAPRI-GOIM trial, 340 KRAS exon 2 wild-type mCRC patients received first-line FOLFIRI plus cetuximab. Tumor samples (182/340, 53.5%) were assessed by NGS to search for mutations in 22 genes involved in colon cancer. Results Objective responses in the NGS cohort were observed in 104/182 patients [overall response rate (ORR) 57.1%; 95% confidence interval (95% CI) 52% to 66.4%] with a median progression-free survival (mPFS) of 9.8 (95% CI 8.7–11.5) months. NGS analysis was successfully completed in all 182 samples. One or more gene mutations (up to five) were detected in 124/182 (68.1%) tumors within 14/22 genes for a total of 206 mutations. KRAS exon 2 mutations were identified in 29/182 (15.9%) samples, defined as wild type by local laboratory assessment. Frequently mutated genes were: TP53 (39.6%), KRAS exons 3/4 (8.8%), NRAS exons 2/3 (7.1%), PIK3CA exons 9/20 (13.2%), BRAF (8.2%). FOLFIRI plus cetuximab treatment determined ORR of 62.0% (95% CI 55.5% to 74.6%) with mPFS of 11.1 (95% CI 9.2–12.8) months in patients with KRAS and NRAS wild-type tumors. Conversely, ORR was 46.6% (95% CI 39.9–57.5%) with mPFS of 8.9 (95% CI 7.4–9.6) months in patients with KRAS or NRAS mutations. Similarly, the subgroup of patients carrying KRAS, NRAS, BRAF, or PIK3CA mutations showed a worse outcome, although this might be due to a prognostic effect. Conclusions This study demonstrates that NGS analysis in mCRC is feasible, reveals high level of intra and intertumor heterogeneity, and identifies patients that might benefit of FOLFIRI plus cetuximab treatment. [ABSTRACT FROM AUTHOR]

AXL and transforming growth factor β (TGF-β) signalling pathways play a key role in modulating tumour microenvironment by promoting epithelial to mesenchymal transition (EMT), stromal activation and regulating immune response in colorectal cancer (CRC). Here we have evaluated the effect of double blockade of TGF-β and AXL receptors, as an innovative therapeutic strategy for CRC. We assessed the correlation of TGF-β and AXL by an in silico analysis of a human CRC gene expression profile database. Afterwards, an evaluation of AXL expression of in a panel of human CRC cell lines by Western Blot (WB) and Real time PCR was performed. The sensitivity of HCT116 and LOVO cells to treatment with galunisertib (LY21209761), a TGF-β R1 inhibitor, and R428, an AXL inhibitor, was assessed by MTT, cell migration, and colony forming assays. Furthermore we generated patient derived 3D spheroid cultures from primary CRC, and tested their susceptibility to galunisertib and R428 by MTT assay. Finally, in vivo experiments were done with HCT116 and LOVO tumour xenografts in immunodeficient mice. In silico analysis showed an association between high expression levels of AXL and TGF-β R1 in CMS4 CRC. AXL was differently expressed on cell lines, and interestingly it resulted increased in HCT116 and LOVO after TGF-β inhibition, probably representing a mechanism of cancer cell escape. Dual blockade with galunisertib and R428 determined a reduction in cell migration of 50% in HCT116 and 37% in LOVO cells, respectively, and colony formation of approximately 90 % in both cell lines. Moreover, combined treatment displayed a strong synergistic activity in 3D cultures derived from five human CRC samples, resulting in the inhibition of proliferation ranging from 80 to 90%. The in vivo experiments of HCT116 and LOVO subcutaneous xenograft models are currently on going and results will be presented. Combined TGF-β and AXL inhibition showed a promising activity in preclinical models of CRC and could represent a novel potential therapeutic strategy for patients with CRC. Università degli studi della Campania "Luigi Vanvitelli". ICURE project, Università degli studi della Campania "Luigi Vanvitelli". D. Melisi: Research grant/Funding (self): Lilly. [ABSTRACT FROM AUTHOR]

Poly-ADP-Ribose Polymerase inhibitors (PARPi) constitute a class of drugs that interfere with DNA damage response and are already available or in current advanced development either alone or in combination with DNA damaging agents such as chemotherapeutics. Some features of colorectal cancer (CRC), like microsatellite instability and MAPK-induced replication stress, make it a good candidate for exploring the combination of PARPi with chemotherapeutics. Previous data have evidenced how PARPi/chemotherapy combinations are effective in various cancers, albeit early clinical trials showed only modest activity in unselected CRC patients. We tested the activity of the PARPi niraparib (MK-4827) used alone or in combination with either 5-fluorouracil, oxaliplatin or irinotecan (SN38) in a panel of 12 CRC cell lines with known molecular characteristics. Proliferation, cell cycle and apoptosis assays were performed. A correlation between combination synergism and the following molecular features was obtained: RAS/BRAF mutation, HER2 amplification, microsatellite status, mutational and transcriptomic profiles from the Cancer Cell Line Encyclopedia (CCLE) database. Mice xenografts using the most representative cell lines are ongoing. Patient-derived 3D primary cultures (PDPCs) are being used to confirm the data obtained in vitro. Niraparib is synergistic with the investigated chemotherapeutics in most of the cell lines explored. The best candidate for combination is SN38, which is synergistic in 9/12 cell lines analysed. MAPK activation, microsatellite instability (MSI) and mutations in genes involved in homologous recombination repair (HRR) are good predictors of synergism. Transcriptomic analysis is ongoing. Mice xenografts and PDPCs models are in progress and will be presented at the Congress. The combination of niraparib and irinotecan/SN38 is effective in an in vitro model of CRC. MAPK activation, MSI and mutation in HRR-associated genes are predictors of synergism and are currently being validated in in vivo and ex vivo models. These findings could lead to a better patient selection for this combination in CRC. The authors. Università della Campania Luigi Vanvitelli; Associazione Italiana per la Ricerca sul Cancro (AIRC). P.P. Vitiello: Research grant/Funding (institution), Travel/Accommodation/Expenses: Amgen; Research grant/Funding (institution): Bayer; Research grant/Funding (institution): Ipsen; Research grant/Funding (institution): Merck; Research grant/Funding (institution): Roche; Travel/Accommodation/Expenses: BMS; Travel/Accommodation/Expenses: Sanofi-Genzyme. D. Ciardiello: Travel/Accommodation/Expenses: Sanofi. C. Cardone: Research grant/Funding (institution): Ipsen; Research grant/Funding (institution): Roche; Research grant/Funding (institution): Merck; Research grant/Funding (institution): Amgen; Research grant/Funding (institution): Bayer. G. Martini: Research grant/Funding (self): Amgen. C. Borrelli: Travel/Accommodation/Expenses: BMS. L. Poliero: Travel/Accommodation/Expenses: BMS. V. De Falco: Travel/Accommodation/Expenses: BMS; Travel/Accommodation/Expenses: Novartis. E.F. Giunta: Travel/Accommodation/Expenses: Novartis; Travel/Accommodation/Expenses: BMS. M. Terminiello: Travel/Accommodation/Expenses: BMS. T. Troiani: Research grant/Funding (institution): Roche; Research grant/Funding (institution): Merck; Research grant/Funding (institution): Bayer; Travel/Accommodation/Expenses: Servier; Travel/Accommodation/Expenses: Amgen; Travel/Accommodation/Expenses: Sanofi; Travel/Accommodation/Expenses: Novartis. F. Ciardiello: Advisory/Consultancy, Research grant/Funding (institution): Merck; Advisory/Consultancy, Research grant/Funding (institution): Bayer; Advisory/Consultancy, Research grant/Funding (institution): Amgen; Advisory/Consultancy, Research grant/Funding (institution): Roche; Advisory/Consultancy: Servier; Advisory/Consultancy: Pfizer; Research grant/Funding (institution): Ipsen. E. Martinelli: Honoraria (self), Research grant/Funding (institution): Amgen; Honoraria (self), Research grant/Funding (institution): Bayer; Honoraria (self), Research grant/Funding (institution): Merck; Research grant/Funding (institution): Roche; Honoraria (self), Research grant/Funding (institution): Servier. All other authors have declared no conflicts of interest. [ABSTRACT FROM AUTHOR]

EPHA2 tyrosine kinase receptor is implicated in tumor progression, stemness phenotype and resistance to treatment in a wide range of cancers. We investigated the effects of GLPG1790, a new selective Eph receptor inhibitor, in colorectal cancer (CRC) across the 4 consensus molecular subtypes (CMS). We tested the antiproliferative effect of GLPG 1790 used alone or in combination with either 5-fluorouracil, oxaliplatin or SN38 (the active metabolite of irinotecan) in a panel of 11 CRC cell lines encompassing the 4 consensus molecular subtypes (CMS). Cell cycle analysis was performed in order to understand possible cell cycle perturbation after treatment. Pathway analysis using western blot (WB) was also performed. We then evaluated the expression of stemness genes upon treatment using qRT-PCR. GLPG 1790 is active in CRC cell lines, with the strongest activity in the cell lines from the CMS4/mesenchymal-like cluster. Combination with chemotherapeutics is not synergistic according to Chou-Talalay model. The selective inhibitor elicits a persistent inactivation of EPHA2 receptor, associated to G0-G1 cell cycle block in the sensitive cell lines. Furthermore, GLPG 1790 is able to decrease the expression of cancer stem cell genes in cell lines belonging to the CMS4 group. EPHA2 blockade using the selective inhibitor GLPG 1790 has a strong antiproliferative effect in the chemorefractory subgroup of CMS4/mesenchymal-like CRC cell lines, associated to a G0-G1 cell cycle arrest. The stronger efficacy of GLPG1790 on the mesenchymal-like subtype is probably due to the impairment of cancer cell stemness and induction of cell differentiation after treatment. The authors. Università della Campania "Luigi Vanvitelli"; Galapagos NV (drug supply); Associazione Italiana per la Ricerca sul Cancro (AIRC). P.P. Vitiello: Travel/Accommodation/Expenses: Amgen; Research grant/Funding (institution): Bayer; Research grant/Funding (institution): Merck; Research grant/Funding (institution): Roche; Research grant/Funding (institution): Servier; Research grant/Funding (institution): Ipsen; Travel/Accommodation/Expenses: BMS; Travel/Accommodation/Expenses: Sanofi. C. Cardone: Research grant/Funding (institution): Amgen; Research grant/Funding (institution): Bayer; Research grant/Funding (institution): Ipsen; Research grant/Funding (institution): Merck; Research grant/Funding (institution): Roche. D. Ciardiello: Travel/Accommodation/Expenses: Sanofi. L. Poliero: Travel/Accommodation/Expenses: BMS. C. Borrelli: Travel/Accommodation/Expenses: BMS. N. Zanaletti: Travel/Accommodation/Expenses: BMS. P. Vitale: Travel/Accommodation/Expenses: BMS. T. Troiani: Honoraria (self), Research grant/Funding (institution): Roche; Honoraria (self), Research grant/Funding (institution): Merck; Honoraria (self), Research grant/Funding (institution): Bayer; Honoraria (self), Travel/Accommodation/Expenses: Amgen; Travel/Accommodation/Expenses: Servier; Travel/Accommodation/Expenses: Sanofi; Travel/Accommodation/Expenses: Novartis. F. Ciardiello: Advisory/Consultancy, Research grant/Funding (institution): Amgen; Advisory/Consultancy, Research grant/Funding (institution): Bayer; Advisory/Consultancy, Research grant/Funding (institution): Roche; Advisory/Consultancy, Research grant/Funding (institution): Merck; Advisory/Consultancy: Servier; Advisory/Consultancy: Pfizer; Research grant/Funding (institution): Ipsen. E. Martinelli: Honoraria (self), Research grant/Funding (institution): Amgen; Honoraria (self), Research grant/Funding (institution): Merck; Honoraria (self), Research grant/Funding (institution): Bayer; Honoraria (self), Research grant/Funding (institution): Roche; Honoraria (self), Honoraria (institution): Servier. All other authors have declared no conflicts of interest. [ABSTRACT FROM AUTHOR]

Anti-PD-1 antibodies represent nowadays a first-choice therapy for metastatic melanoma patients. Despite impressive results in terms of PFS and OS, a proportion of patients does not respond to anti-PD-1 therapy with an overall poor prognosis. Identification of predictive biomarkers is considered an important unmet clinical need to avoid expensive and potentially harmful drugs in patients who will not respond to them. In the last years, many studies have evaluated the role of cytokines on both blood and tissue samples as predictive biomarkers for immunotherapy, with encouraging results. Blood samples from 18 patients with metastatic melanoma treated with anti-PD-1 antibodies as first line therapy were collected at baseline. 8 patients were classified as non-responders (best response: PD excluding pseudo-progression with median PFS of 2 months) and 10 patients as responders (best response: PR or CR, with median PFS of 17 months). mRNA expression levels of the main pro- and anti-inflammatory cytokines were evaluated by Real time quantitative PCR in PBMCs obtained from baseline blood samples. Unpaired two-tailed t-test was used for statistical analysis. IFN-γ mRNA expression levels were higher in responder patients (p < 0.01) whereas IL-10 levels tended to be higher in non-responders (p > 0.05). Combining data for each patient, we noticed a correlation between higher levels of IFN-γ and lower levels of IL-10 for responders and vice versa. Starting from these findings, we observed that the IFN-γ/IL-10 ratio was higher (median: 43,3 vs 5,2) in responders (p < 0.01), with high negative and positive predictive value (NPV:100% and PPV:91% using a threshold of 18). The main lymphocyte subpopulations producing these cytokines were also identified. Our data suggest an interesting correlation between IFN-γ/IL-10 ratio and response to anti-PD-1 therapy in melanoma patients. This correlation seems to be stronger than using IFN-γ expression levels alone probably because of the influence of anti-inflammatory cytokines. Since this is an exploratory and retrospective analysis of 18 patients, a larger population should be tested to validate our results. Dipartimento di Medicina di Precisione, Università degli studi della Campania Luigi Vanvitelli. Has not received any funding. F. Ciardiello: Advisory / Consultancy: Roche; Advisory / Consultancy: Amgen; Advisory / Consultancy: Merck; Advisory / Consultancy: Sanofi; Advisory / Consultancy: Bayer; Advisory / Consultancy: Pfizer; Advisory / Consultancy: Servier; Advisory / Consultancy: BMS; Advisory / Consultancy: Cellgene; Advisory / Consultancy: Lilly; Research grant / Funding (institution): Bayer; Research grant / Funding (institution): Roche; Research grant / Funding (institution): Merck; Research grant / Funding (institution): AstraZeneca; Research grant / Funding (institution): Amgen; Research grant / Funding (institution): Takeda. T. Troiani: Research grant / Funding (institution): Roche; Research grant / Funding (institution): Sanofi; Research grant / Funding (institution): Merck; Research grant / Funding (institution): Amgen; Research grant / Funding (institution): Servier; Research grant / Funding (institution): Novartis; Research grant / Funding (institution): Bayer. All other authors have declared no conflicts of interest. [ABSTRACT FROM AUTHOR]

Molecular mechanisms driving acquired resistance to anti-EGFR therapies in metastatic Colorectal Cancer (mCRC) are complex but generally involve the activation of the downstream RAS-RAF-MEK-MAPK pathway. In order to understand the mechanism underlying MEK inhibitor (MEKi) resistance, we generated three different MEKi resistant models, two all RAS WT (SW48-MR and LIM1215-MR) and one mutated in RAS (HCT116-MR). These models showed features related to the gene signature of Colorectal Cancer CMS4 with upregulation of immune pathway as confirmed by Microarray and Western blot analysis. In particular, moving forward the MEKi phenotype we assisted to the loss of epithelial features and acquisition of mesenchymal markers and morphology. Moreover, this change in the morphology is accompanied by up-regulation of PD-L1 expression and activation of EGFR and its downstream pathway, independently of cell line status mutation. To extend these in vitro findings, we performed an in vivo study using MC38 and CT26 MEKi resistant syngeneic models that we have previously generated. Combined treatment of MEKi, EGFR inhibitor (EGFRi) and PD-L1inhibitor (PD-L1i) resulted in a marked inhibition of tumor growth in both MC38–MR and CT26-MR xenograft model. These results suggest a strategy to potentially overcome immunotherapy resistance in CMS4-like tumors and to improve the efficacy of MEK inhibition by co-treatment with other agents providing an additional therapeutic strategy via modulation of host immune responses. The authors. Has not received any funding. All authors have declared no conflicts of interest. [ABSTRACT FROM AUTHOR]