In CRC, reports of CLDN1 expression have been contradictory. Pembrolizumab order For example, overexpression of CLDN1 in adenocarcinoma tissue in comparison to normal mucosa has been reported [32], [33] and [34], and more recently, Bezdekova et al. demonstrated elevated CLDN1 expression in a cohort of 42 adenomas relative to normal epithelium [35]. In these studies, cytoplasmic CLDN1 was correlated with disease progression. However, low CLDN1 tumor expression has also been observed and a link

between metastasis and poor patient prognosis has been proposed [36], [37] and [38]. These studies, however, did not report on molecular characterization of the patient samples tested, and it is possible that these opposing results can be explained by molecular features such as BRAF mutation status, MSI, or CIMP. Further studies on our patient cohort exploring the association signaling pathway between mutations in the BRAF gene, CLDN1 staining, and patient outcome are warranted to better understand their use for prognosis. The dysregulation of CLDN1 expression has also been postulated as a contributor to colon cancer progression and its up-regulation has been shown to be associated with the disorganization of tight junction

fibrils, leading to an increase in paracellular permeability [32]. CLDN1 expressing xenograft tumors have been demonstrated to have increased potential for invasion and metastatic behaviour [39]. In addition, a positive correlation of CLDN1 expressing CRC cells and their resistance

to anoikis also suggests that CLDN1 may influence tumor growth and evolution [40]. The role of CLDN1 in the progression of SSA to cancer has not been investigated and is unknown. However, the evolution of serrated lesions to CRC appears to be accelerated and faster than conventional adenomas [18] and [41] and may be related to resistance to anoikis and cellular discohesion. As CLDN1 is associated with both processes, the serrated polyps showing CLDN1 overexpression Meloxicam may have increased potential for progression to higher grade lesions through the serrated pathway neoplasia. In gastric epithelial cells, CLDN1 has also been described as a target of the RUNX3 transcription factor [42]. In intestinal tumors, RUNX3 can potentially inactivate Wnt signaling by interacting with the β-catenin/TCF4 complex [43]. RUNX3 is one of the core genes used to classify CIMP high CRC [5] and it is possible that in this subset of tumors, promoter hypermethylation and subsequent loss of RUNX3 expression can attenuate β-catenin/TCF signaling leading to elevated CLDN1 expression. Activation of Wnt signaling in SSA/P is controversial with evidence in the literature to both support and oppose this hypothesis. Abnormal β-catenin staining has been shown in a subset of SSA/P, and Yachida et al. have reported an association between nuclear β-catenin staining and BRAF V600E mutation [44], [45] and [46]).