Tumor DNA mismatch repair (MMR) deficiency testing is important to the identification of Lynch syndrome and decision making regarding adjuvant chemotherapy in stage II colorectal cancer (CRC) and has become an indispensable test in metastatic tumors due to the high efficacy of immune checkpoint inhibitor (ICI) in deficient MMR (dMMR) tumors. CRCs greatly benefit from this testing as approximately 15% of them are dMMR but only 3% to 5% are at a metastatic stage. MMR status can be determined by two different methods, microsatellite instability (MSI) testing on tumor DNA, and immunohistochemistry of the MMR proteins on tumor tissue. Recent studies have reported a rate of 3% to 10% of discordance between these two tests. Moreover, some reports suggest possible intra- and inter-tumoral heterogeneity of MMR and MSI status. These issues are important to know and to clarify in order to define therapeutic strategy in CRC. This review aims to detail the standard techniques used for the determination of MMR and MSI status, along with their advantages and limits. We review the discordances that may arise between these two tests, tumor heterogeneity of MMR and MSI status, and possible explanations. We also discuss the strategies designed to distinguish sporadic versus germline dMMR/MSI CRC. Finally, we present new and accurate methods aimed at determining MMR/MSI status.

In colorectal cancer, KRAS (exons 2, 3, and 4) and NRAS (exons 2, 3, and 4) mutations are associated with resistance to antiepidermal growth factor receptor monoclonal antibodies, and BRAF mutation is a molecular marker of poor prognosis. KRAS exon 2 and BRAF-mutated colorectal cancers have well-known distinct clinicopathological characteristics. Comparison of tumors with different RAS status (exons 2, 3, and 4 of KRAS and NRAS) based on their clinicopathological characteristics has never been established. All colorectal cancer patients with RAS and BRAF testing from 2011 to 2015 were included in this observational retrospective study. Patient and tumor characteristics were collected and correlation with RAS and BRAF status was evaluated. A total of 1735 patients with colorectal cancer were included. RAS-mutated colorectal cancers (n=1002), compared with RAS wild-type colorectal cancers (n=733), were significantly associated with male gender, classical adenocarcinoma subtype, well/moderately differentiated tumors, and microsatellite stable phenotype. KRAS codon 13-mutated colorectal cancers (n=171), compared with RAS wild-type colorectal cancers, more frequently presented classical adenocarcinoma subtype and microsatellite stable phenotype. In comparison with other RAS mutations, KRAS exon 3-mutated colorectal cancers (n=23) were associated with mucinous/rare histological subtypes and, most likely to located in the rectum. KRAS exon 4-mutated colorectal cancers (n=33) were more frequently associated with mucinous/rare histological subtypes. There was no significant association between NRAS mutation (n=37) and clinicopathological features. Colorectal cancers are associated with different clinicopathological features according to the type of RAS mutation. Consequently, these particular characteristics must be considered when assessing the prognostic value of RAS status in colorectal cancer.

Organic cation/carnitine transporters (OCT/N) mediate uptake of positively charged molecules. Their role in lung epithelium, however, is not well understood. OCT/N expression and activity was studied in cell lines of human alveolar (A549), bronchial (16HBE14o-and Calu-3) and intestinal (Caco-2) epithelium. Protein levels were largely comparable for all OCT/Ns in the respiratory epithelial cell lines studied, however, OCT2 was exclusively observed in A549 cells. OCT1 and -2 were present at significantly higher levels in Caco-2 cells, compared with the pulmonary epithelial cell types. OCTN1 and -2 were also more abundant in Caco-2. Only OCT3 was expressed evenly across all cell lines investigated. .5 μM, respectively. This uptake was sensitive to organic cations, but insensitive to carnitine and lysine. We conclude that uptake of organic cations is facilitated by distinct pathways in different regions of lung mucosa. Luminally localised OCT2 appears to be exclusively involved in the alveolar epithelium, whereas basolateral localised OCT3 might play a role in alveolar as well as in bronchial epithelial cells.