The cellular prion protein controls the mesenchymal-like molecular subtype and predicts disease outcome in colorectal cancer.

BACKGROUND: Comprehensive transcriptomic analyses have shown that colorectal cancer (CRC) is heterogeneous and have led to the definition of molecular subtypes among which the stem-cell, mesenchymal-like group is associated with poor prognosis. The molecular pathways orchestrating the emergence of this subtype are incompletely understood. In line with the contribution of the cellular prion protein PrPC to stemness, we hypothesize that deregulation of this protein could lead to a stem-cell, mesenchymal-like phenotype in CRC. METHODS: We assessed the distribution of the PrPC-encoding PRNP mRNA in two large CRC cohorts according to molecular classification and its association with patient survival. We developed cell-based assays to explore the impact of gain and loss of PrPC function on markers of the mesenchymal subtype and to delineate the signalling pathways recruited by PrPC. We measured soluble PrPC in the plasmas of 325 patients with metastatic CRC and probed associations with disease outcome. FINDINGS: We found that PRNP gene expression is enriched in tumours of the mesenchymal subtype and is associated with poor survival. Our in vitro analyses revealed that PrPC controls the expression of genes that specify the mesenchymal subtype through the recruitment of the Hippo pathway effectors YAP and TAZ and the TGFß pathway. We showed that plasma levels of PrPC are elevated in metastatic CRC and are associated with poor disease control. INTERPRETATION: Our findings define PrPC as a candidate driver of the poor-prognosis mesenchymal subtype of CRC. They suggest that PrPC may serve as a potential biomarker for patient stratification in CRC. FUNDING: Grant support was provided by the following: Cancéropôle Ile de France (grant number 2016-1-EMERG-36-UP 5-1), Association pour la Recherche sur le Cancer (grant number PJA 20171206220), SATT Ile de France Innov (grant number 415) as well as INSERM.

Association of Prognostic Value of Primary Tumor Location in Stage III Colon Cancer With RAS and BRAF Mutational Status.

Importance: We know of no data on the prognostic value of primary tumor location (PTL) according to BRAF, RAS, and microsatellite instability (MSI) status in patients who have undergone resection for colon cancer (CC) and have been treated with current standard adjuvant chemotherapy. Objective: To determine the prognostic and predictive value of PTL according to BRAF, RAS, and MSI status in patients with stage III CC receiving adjuvant treatment with FOLFOX (folinic acid [leucovorin calcium], fluorouracil, and oxaliplatin) with or without cetuximab. Design, Setting, and Participants: This post hoc analysis included patients with available tumor blocks of resected stage III colon adenocarcinoma who participated in the Pan-European Trials in Alimentary Tract Cancer (PETACC)-8 phase 3 randomized trial. Among the 2559 patients who underwent randomization, 1900 were screened by next-generation sequencing, which showed that 1869 had full information concerning PTL. We categorized primary tumor site as located proximal (right) or distal (left) to the splenic flexure. Main Outcomes and Measures: The associations between PTL (right- vs left-sided) and disease-free survival (DFS), survival after relapse (SAR), and overall survival (OS) were assessed by Cox models and adjusted for clinical and pathological features, treatment, and MSI, BRAF, and RAS status. Results: Among the 1869 patients (1056 [57%] male; mean [SD] age, 59.4 [9.5] years) with full molecular data analyzed, 755 (40%) had a right-sided tumor, 164 (10%) had MSI, 942 (50%) had RAS mutations, and 212 (11%) had BRAF mutations. Right-sided tumor location was not prognostic for DFS in the whole population but was associated with a shorter SAR (hazard ratio [HR], 1.54; 95% CI, 1.23-1.93; P = .001) and OS (HR, 1.25; 95% CI, 1.02-1.54; P = .03). When looking at DFS in the different molecular subgroups, we found similar results for microsatellite-stable tumors and tumors with MSI; a better DFS in right-sided vs left-sided tumors in patients with RAS mutations (HR, 0.80; 95% CI, 0.64-1.00; P = .046); and a worse DFS in right-sided vs left-sided tumors in patients with RAS and BRAF double wild type (HR, 1.39; 95% CI, 1.01-1.92; P = .04). These results were found independently of the treatment received, and no beneficial effect of cetuximab on DFS or OS was observed in left-sided tumors. Conclusions and Relevance: Although right-sided tumor location is associated with poor survival in patients with metastatic CC as previously reported, the association with disease recurrence appears to vary for patients with stage III CC and RAS or BRAF mutations vs those with double wild type.