Purpose: No biomarker to personalize treatment in locally advanced rectal cancer (LARC) is currently available. We assessed in LARC whether a diagnostic biopsy-adapted immunoscore (IS B) could predict response to neoadjuvant treatment (nT) and better define patients eligible to an organ preservation strategy ("Watchand-Wait"). Experimental Design: Biopsies from two independent cohorts (n 1 ¼ 131, n 2 ¼ 118) of patients with LARC treated with nT followed by radical surgery were immunostained for CD3 þ and CD8 þ T cells and quantified by digital pathology to determine IS B. The expression of immune-related genes post-nT was investigated (n ¼ 64 patients). Results were correlated with response to nT and disease-free survival (DFS). The IS B prognostic performance was further assessed in a multicentric cohort (n ¼ 73 patients) treated by Watch-and-Wait. Results: IS B positively correlated with the degree of histologic response (P < 0.001) and gene expression levels for Th1 orientation and cytotoxic immune response, post-nT (P ¼ 0.006). IS B high identified patients at lower risk of relapse or death compared with IS B low [HR, 0.21; 95% confidence interval (CI), 0.06-0.78; P ¼ 0.009]. Prognostic performance of IS B for DFS was confirmed in a validation cohort. IS B was an independent parameter, more informative than pre-(P < 0.001) and post-nT (P < 0.05) imaging to predict DFS. IS B combined with imaging post-nT discriminated very good responders that could benefit from organ preservation strategy. In the "Watch-and-Wait" cohort (n ¼ 73), no relapse was observed in patients with IS B high (23.3%). Conclusions: IS B predicts response to nT and survival in patients with LARC treated by surgery. Its usefulness in the selection of patients eligible for a Watch-and-Wait strategy is strongly suggested.

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.

Colorectal cancer (CRC) is the third most commonly diagnosed cancer worldwide and clinical outcome has improved substantially during the last two decades with targeted therapies. The immune system has a major role in cancers, especially the CD8 + T cells specific to tumor antigens. However, tumors can escape immune response by different mechanisms including upregulation of inhibitory immune checkpoint receptors, such as well-known Programmed cell Death protein-1 (PD-1)/Programmed cell Death Ligand 1 (PD-L1) interaction, leading CD8 + T cells to a state of anergy. Immunotherapy, with the so-called immune checkpoint inhibitors (CPIs), has recently been approved in treatment of multiple cancers due to its prolonged disease control and acceptable toxicities. The recent groundbreaking success involving anti-PD-1 CPIs in metastatic CRC with deficient mismatch repair system (dMMR) is promising, with several trials ongoing. Major challenges are ahead in order to determine how, when and for which patients we should use these CPIs in CRC. Areas covered: This review highlights some promises and challenges concerning personalized immunotherapy in CRC. First results and ongoing breakthrough trials are presented. The crucial role of biomarkers in selecting patient is also discussed. Expert opinion: As of now, dMMR and POLE mutations (DNA polymerase ε) with ultramutator phenotype are the most powerful predictive biomarkers of CPI efficacy. The most challenging issue is pMMR mCRC and determination of how to convert a 'nonimmunogenic' neoplasm into an 'immunogenic' neoplasm, a combination of CPIs with radiation or MEK inhibitor probably being the most relevant strategy. Next-generation sequencing (NGS) assays to quantify mutational load could be more reliable predictive biomarkers of CPIs efficacy than PD-L1 expression or immune scores.

Background: DNA mismatch repair system deficiency (dMMR) is found in 15% of colorectal cancers (CRCs). Two methods are used to determine dMMR, immunohistochemistry (IHC) of MMR proteins and molecular testing of microsatellite instability (MSI). Only studies with a low number of patients have reported rates of discordance between these two methods, ranging from 1% to 10%. Materials and methods: Overall, 3228 consecutive patients with CRCs from two centers were included. Molecular testing was carried out using the Pentaplex panel and IHC evaluated four (MLH1, MSH2, MSH6, and PMS2; cohort 1; n ¼ 1085) or two MMR proteins (MLH1 and MSH2; cohort 2; n ¼ 2143). The primary endpoint was the rate of discordance between MSI and MMR IHC tests.Results: Fifty-one discordant cases (1.6%) were initially observed. Twenty-nine out of 51 discordant cases were related to IHC misclassifications. In cohort 1, after re-reading IHC and/or carrying out new IHC, 16 discordant cases were reclassified as nondiscordant. In cohort 2, after the addition of MSH6/PMS2 IHC and re-examination, 13 were reclassified as nondiscordant. In addition, 10 misclassifications of molecular tests were identified. Finally, only 12 discordant cases (0.4%) remained: 5 were proficient MMR/MSI and 7 were dMMR/microsatellite stable. Conclusions: Our study confirmed the high degree of concordance between MSI and MMR IHC tests. Discordant cases must be reviewed, and if needed, tests must be repeated and analyzed by an expert team.

Background: In most countries, participation in colorectal cancer (CRC) screening programs with the immunological fecal occult blood test (iFOBT) is low. Mutations of RAS and BRAF occur early in colorectal carcinogenesis and “liquid biopsy” allows detection of mutated circulating tumor DNA (ctDNA). This prospective study aims to evaluate the performance of RAS and BRAF-mutated ctDNA in detecting CRC and advanced adenomas (AA). Methods: One hundred and thirty patients who underwent colonoscopy for suspicion of colorectal lesion were included and divided into four groups: 20 CRC, 39 AA, 31 non-advanced adenoma and/or hyperplastic polyp(s) (NAA) and 40 with no lesion. Mutated ctDNA was analyzed by droplet digital PCR. Results: ctDNA was detected in 45.0% of CRC, in 2.6% of AA and none of the NAA and “no-lesion” groups. All patients with stage II to IV mutated CRC had detectable ctDNA (n = 8/8). Among the mutated AA, only one patient had detectable ctDNA (4.3%), maybe due to limited technical sensitivity or to a low rate of ctDNA or even the absence ctDNA in plasma. Specificity and sensitivity of KRAS- and BRAF-mutated ctDNA for the detection of all CRC and AA were 100% and 16.9%, respectively. Conclusions: ctDNA had high sensitivity in detection of advanced mutated CRC but was unable to sensitively detect AA. ctDNA analysis was easy to perform and readily accepted by the population but requires combination with other circulating biomarkers before replacing iFOBT.