An everyday clinical practice dilemma in the 20–30% of metastatic colorectal cancer (CRC) patients that have not been operated on their primary tumour, is, under which specific histopathology and molecular circumstances, an endoscopic biopsy could be considered adequate to provide a representative RAS/BRAF molecular status to guide treatment. A consecutive series of 193 paired biopsy and primary CRC tumour samples between August 2008 and 2010 available in the Department of Pathology archives, University Hospitals, KU Leuven were retrieved. For a pair to be included, in the endoscopic biopsy, 20% of invasive adenocarcinoma cells should be present and enough slides to yield an extracted DNA concentration of ⩾5 ng μl−1, and no <2 ng μl−1 should be available for cutting. Exons 2–4 KRAS/NRAS, BRAF, PIK3CA molecular evaluation was performed with RT–PCR and Sequenom. From 165 deemed adequate by the pathologist pairs, 85 (51.5%) were concordantly mutated in at least one of the tested genes, 70 (42.5%) were wt and 10 (6%) were discordant, harbouring a mutation in the primary and not in the endoscopic biopsy. In the re-evaluation, when more slides were cut per discordant pair, mutational status changed in two of the six discordantly KRAS-mutated pairs. A strong strength of agreement for both runs was observed (Cohen's kappa, k=0.877, P<0.001 and k=0.901, P<0.001, respectively) between the surgically acquired and the endoscopic biopsy specimens’ evaluation. Based on our results, an endoscopic biopsy could provide an accurate mutational profile and become a justified alternative to a surgically removed primary tumour specimen, as long as specific histopathology criteria are met.

ABSTRACT Background The RAS/RAF/MEK/MAPK and the PTEN/PI3K/AKT/mTOR pathways are key intracellular signal transduction pathways for the control of survival and proliferation in human cancer cells. Selective inhibitors of different transducer molecules in these pathways have being developed as molecular targeted anti-cancer therapies. Methods The in vitro and in vivo antitumor activity of pimasertib, a selective MEK ½ inhibitor, alone or in combination with a PI3K inhibitor (PI3Ki), a mTOR inhibitor (everolimus), or with multitargeted kinase inhibitors (sorafenib and regorafenib) were tested in a panel of eleven human lung and colon cancer cell lines. Results Following pimasertib treatment, the cancer cell lines were classified as pimasertib-sensitive (IC50 for cell growth inhibition of approximately 0.001 µM) or pimasertib-resistant (IC50 for cell growth inhibition above 3 µM). Evaluation of basal gene expression profiles by microarrays identified a series of genes that were up-regulated in pimasertib-resistant cancer cells and that were involved in both RAS/RAF/MEK/MAPK and PTEN/PI3K/AKT/mTOR pathways. Therefore, a series of combination experiments with pimasertib and either PI3Ki, everolimus, sorafenib or regorafenib were conducted, demonstrating a synergistic effect in cell growth inhibition, G1 phase arrest and induction of apoptosis with a sustained blockade in MAPK- and AKT-dependent signaling pathways in pimasertib-resistant human colon carcinoma (HCT15) and lung adenocarcinoma (H1975) cells. Finally, in nude mice bearing established HCT15 and H1975 subcutaneous tumor xenografts, the combination treatment with pimasertib and BEZ235 (a dual PI3K/mTOR inhibitor) or with sorafenib caused significant tumor growth delays and increase in mice survival as compared to single agent treatment. Conclusion These results suggest that it is possible to overcome intrinsic resistance to MEK inhibition by the dual blockade of MAPK and PI3K pathways. Disclosure All authors have declared no conflicts of interest.

ABSTRACT Introduction Previous analysis of the gene expression data of mutational subgroups in the PETACC3 trial, revealed a very homogenous gene expression pattern in BRAF mutant CRC patients; while KRAS mutant CRC contain at least three different patient groups in terms of gene expression. One of these KRAS mutant groups together with 10% of KRAS/BRAF WT (WT2) patients, resembled the gene expression found in the BRAF mutants. This BRAF-like subgroup is characterized by poor prognosis. In this article we investigate, if heterogeneity in CRC patients can be partly explained by diverse signaling downstream of KRAS, to which the DUSPs take part. Material and methods The expression of DUSP1, DUSP4 and DUSP6, DUSPs previously shown to be induced by mutations in genes of the MAPK pathway, was analyzed in 4 different CRC patient microarray datasets (PETACC3, cetuximab, TCGA and Agendia dataset). We investigated, if patients with low and high DUSP expression behave differently in terms of response, OS, PFS and differ in clinical characteristics both in PETACC3 and TCGA dataset. Findings Unlike DUSP1, DUSP4 and DUSP6 were differentially overexpressed between BRAF mutants and KRAS mutants on one side and between BRAF mutants and WT2 patients on the other side. When we subdivided the patients into low and high DUSP expression within KRAS mutant and WT2 patients, we found a significant difference in OS in both mutational subgroups with high DUSP4 expression in KRAS mutants associated with a better OS and in WT2 associated with a worse OS. Multivariate analysis in the BRAF WT patients in both PETACC3 and cetuximab dataset showed that high DUSP4 expression was still associated with a worse OS (HR = 1.23; p Conclusions DUSP4 is predictive for OS in CRC patients with KRAS mutations. Interestingly, within KRAS mutant and WT2 patients high DUSP4 expression correlates with clinical characteristics that are typical for BRAF mutant CRC patients. If DUSP4 may represent a novel biomarker for a subset of CRC patients needs further research. Download : Download full-size image Fig. 1 . Box plots with DUSP4 expression according to different mutational groups in PETACC3 dataset. Download : Download full-size image Fig. 2 . Kaplan-Meier curve for overall survival according to DUSP4 expression (low and high) in KRAS WT patients.