The Day-To-Day Practice of MMR and MSI Assessment in Colorectal Adenocarcinoma: What We Know and What We Still Need to Explore.

BACKGROUND: The DNA mismatch repair (MMR) system is a highly preserved protein complex recognizing short insertions, short deletions, and single base mismatches during DNA replication and recombination. MMR protein status is identified using immunohistochemistry. Deficit in one or more MMR proteins, configuring deficient MMR status (dMMR), leads to frameshift mutations particularly clustered in microsatellite repeats. Thus, microsatellite instability (MSI) is the epiphenomenon of dMMR. In colorectal cancer (CRC), MMR/MSI status is a biomarker with prognostic and predictive value of resistance to 5-fluorouracil and response to immune checkpoint inhibitor therapy. SUMMARY: In this Review, we describe the challenges the practicing pathologist may face in relation to the assessment of MMR/MSI status and any open issues which still need to be addressed, focusing on pre-analytic issues, pitfalls in the interpretation, and technical aspects of the different assays. KEY MESSAGES: The current methods of detecting dMMR/MSI status have been optimized for CRCs, and whether these techniques can be applied to all tumor and specimen types is still not fully understood. Following the Food and Drug Administration (FDA), tissue/site agnostic drug approval of pembrolizumab for advanced/metastatic MSI tumors, MMR/MSI status in gastrointestinal tract is a common request from the oncologist. In this setting, several issues still need to be addressed, including criteria for sample adequacy.

Histopathology of inflammatory bowel disease - Position statement of the Pathologists of the Italian Group for the Study of Inflammatory Bowel Disease (IG-IBD) and Italian Group of Gastrointestinal Pathologists (GIPAD-SIAPEC).

Diagnosis of the inflammatory bowel diseases ulcerative colitis (UC) and Crohn's disease (CD) relies mainly on the histopathological examination of endoscopic biopsies of the gastrointestinal tract. To facilitate the accurate diagnosis of these two conditions, this paper addresses key issues on the: (A) gastrointestinal biopsy procedure, (B) histomorphological characteristics of UC and CD, and (C) diagnosis of dysplasia. The 13 statements presented here represent the consensus of two groups of Italian pathologists (IG-IBD and GIPAD).

Prognostic relevance of histopathological features in signet ring cell carcinoma of the colorectum.

Signet ring cell carcinoma (SRCC) is a rare variant of colorectal cancer (CRC), by definition composed of at least 50 % of neoplastic cells showing signet ring cell morphology. Colorectal SRCC is mainly characterized by aggressive clinical behavior, high pTNM stage and microsatellite instability (MSI). We assessed the prognostic value of several histopathological parameters (histological grade, venous invasion, lymphovascular invasion, MSI, mucin content, tumour budding, pTNM stage) in terms of disease free survival (DFS) and cancer specific survival (CSS) in a series of 32 SRCCs. We confirm that pTNM stage at diagnosis is relevant for predicting DFS and CSS in SRCC. In addition, we show on haematoxylin and eosin or immunohistochemically stained (CD34, podoplanin) sections that venous invasion and lymphovascular invasion are significantly associated with shorter DFS and CSS in SRCC. Notably, venous invasion assed by immunohistochemistry had the highest risk ratio and proved to be the only independent prognostic variable. Finally, we show that histological grade, as assessed on the percentage of formed glands, has prognostic relevance in SRCC as high-grade tumours (<50 % of glands) had significantly shorter CSS compared to low-grade tumours. This remained an independent variable at multivariate analysis. If our findings are confirmed in further studies, venous invasion as assessed by immunohistochemistry and histological Tgrade might be added to guidelines for SRCC reporting as significant prognostic factors.

Intestinal anisakidosis: histopathological findings and differential diagnosis.

Anisakidosis is a human zoonotic disease caused by the ingestion of raw or undercooked or not adequately salted, pickled, or smoked fish containing larval nematodes of the Anisakis species. The incidence of this infection is higher in geographical zones with traditional consumption of raw fish. However, in the last years, prevalence raised in low risk zones due to the increase popularity of Asian cuisine. According to where the larvae settle in the gastrointestinal tract, anisakidosis may have different clinical symptoms. In particular, intestinal anisakidosis may mimic several surgical conditions, including appendicitis, ileitis, diverticulitis or inflammatory bowel disease. For this reason, diagnosis is often histopathological. In the present paper, we describe the clinico-pathological findings of six novel cases of intestinal anisakidosis occurred in southern Italy, and provide clues for the differential diagnosis toward Crohn's disease and eosinophilic enteritis, which have similar histopathological characteristics. Awareness of the existence of intestinal anisakidosis may facilitate its recognition and correct diagnosis, which is of fundamental importance for appropriate therapeutic approach.

Poorly differentiated clusters (PDCs) as a novel histological predictor of nodal metastases in pT1 colorectal cancer.

The practical use of histological factors such as submucosal (SM) invasion depth, poor differentiation, presence of lymphovascular invasion (LVI) and tumour budding to establish the risk of nodal dissemination in pT1 colorectal cancer (CRC) is limited by their low standardization and high inter-observer variability. It was recently suggested that the presence in CRC histological sections of poorly differentiated clusters (PDCs), defined as ≥5 cancer cells with no gland formation, may predict the metastatic potential of CRC. In addition, PDC assessment was shown to be more reproducible than the evaluation of the other aforementioned histological predictors. Hence, in this study, we investigated and compared the predictive value of PDC and other histological parameters on the risk of nodal involvement in pT1 CRC. The presence of PDC, SM invasion depth ≥1,000 µm and LVI was significantly associated with N+ status in pT1 CRC (P < 0.0001). Among these parameters, SM invasion depth had the highest sensitivity to identify N+ pT1 CRC but with the lowest specificity. When the analysis was restricted to CRCs with SM invasion depth ≥1,000 µm, the presence of PDC was the only independent risk factor for nodal metastases and allowed the identification of 87.5 % of N+ cancers. In conclusion, in this study, we demonstrate that the presence of PDC is associated with the metastatic potential of pT1 CRC. The combination of this parameter with SM invasion depth may allow identifying most of the pT1 CRC with nodal metastases.

Histologic grading based on counting poorly differentiated clusters in preoperative biopsy predicts nodal involvement and pTNM stage in colorectal cancer patients.

Histologic grading is commonly assessed in colorectal cancer preoperative biopsies. Nevertheless, its clinical impact is limited by low interobserver reproducibility and poor concordance with grading found in the final resection specimen. In the present study, we aimed to investigate the reproducibility, accuracy, and predictive value on lymph node status or pTNM stage of a novel grading system based on the number of poorly differentiated clusters in colorectal cancer preoperative endoscopic biopsies. Grading based on counting poorly differentiated clusters was assessed in 163 colorectal cancer endoscopic biopsies and corresponding surgical specimens. With this system, 152 biopsies could be graded with good interobserver agreement (κ = 0.735). In comparison with the surgical specimens, 75% of colorectal cancers were correctly graded in the biopsy, and 81% of poorly differentiated colorectal cancers were identified at initial biopsy. High poorly differentiated clusters grade in the biopsy was significantly associated with nodal metastasis, high pTNM stage (P < .0001), or histologic features suggestive of more aggressive behavior (tumor budding, perineural invasion, vascular invasion, and infiltrating tumor border) in the surgical specimen. Furthermore, this system identified colorectal cancer with nodal involvement or high pTNM stage with a 78% positive predictive value and 71% and 69% negative predictive values, respectively. Our findings suggest that a grading system based on the quantification of poorly differentiated clusters is feasible in most colorectal cancer endoscopic biopsies. In view of its good reproducibility, accuracy, and predictive value on the anatomical extent of the disease, it may be taken into account for decision-making in colorectal cancer treatment.

Detection of KRAS mutations in colorectal cancer with Fast COLD-PCR.

Patients with metastatic colorectal carcinoma (mCRC) carrying activating mutations of the KRAS gene do not benefit from treatment with anti-epidermal growth factor receptor (EGFR) monoclonal antibodies. Therefore, KRAS mutation testing of mCRC patients is mandatory in the clinical setting for the choice of the most appropriate therapy. Co-amplification-at-lower denaturation-temperature PCR (COLD-PCR) is a novel modification of the conventional PCR method that selectively amplifies minority alleles from a mixture of wild-type and mutant sequences irrespective of the mutation type or position within the sequence. In this study, we compared the sensitivity of a COLD-PCR method with conventional PCR/sequencing and the real-time PCR-based Therascreen kit to detect KRAS mutations. By using dilutions of KRAS mutant DNA in wild-type DNA from colon cancer cell lines with known KRAS status, we found that Fast COLD-PCR is more sensitive than the conventional PCR method, showing a sensitivity of 2.5% in detecting G>A and G>T mutations. The detection of G>C transversions was not improved by either Fast COLD-PCR or Full COLD-PCR. We next analyzed by COLD-PCR, conventional PCR and Therascreen 52 formalin-fixed paraffin-embedded samples from mCRC patients. Among 36 samples with >30% tumor cells, 8 samples were negative by conventional PCR, Therascreen and Fast COLD-PCR; 20 mutations identified by conventional PCR were confirmed by Therascreen and Fast COLD-PCR; 8 cases undetermined by conventional PCR were all confirmed to carry KRAS G>A or G>T mutations by using either Therascreen or Fast COLD-PCR. Conventional PCR was able to detect only 2 KRAS mutations among 16 samples with <30% tumor cells (12.5%), whereas Therascreen and Fast COLD-PCR identified 6 mutants (37.5%). These data suggest that Fast COLD-PCR has a higher clinical sensitivity as compared with conventional PCR in detecting G>C to A>T changes in the KRAS gene, which represent >90% of the mutations of this oncogene in CRC.

Enteric neuropathology of the terminal ileum in patients with intractable slow-transit constipation.

Slow-transit constipation is usually considered a colonic motor disorder. However, there is some evidence that abnormalities may be present in locations other than the colon. In particular, several studies have reported abnormal motor activity of the small bowel in these patients. We evaluated the neuropathological aspects of the terminal ileum in patients with slow-transit constipation to see whether abnormalities are present that may explain an abnormal motility of the small intestine. Specimens of the terminal ileum were obtained from 16 female patients (age range, 42-76 years) with slow-transit constipation undergoing surgery for intractable symptoms. Fifteen age- and sex-matched controls were used for comparison. Histologic and immunohistochemical evaluation of the myenteric plexus and the smooth muscle of the proximal ileal resection margin was carried out by means of hematoxylin and eosin, trichrome and periodic acid-Schiff stain, neuron-specific enolase, S-100, CD117, CD34, anti-alpha-actin, desmin, and vimentin antibodies. The patient group displayed a significantly reduced number of glial cells, compared with controls, in both the submucosal and the myenteric plexus. Only 1 of the 3 populations of interstitial cells of Cajal (that associated with the deep muscular plexus) was decreased in patients. No differences were found between patients and controls concerning ganglia neurons, fibroblast-like cells, enteric neurons, apoptotic phenomena, and smooth muscle. Patients with slow-transit constipation display neuropathological abnormalities of the terminal ileum to a lesser extent than those we previously found in the colon, which might explain the abnormal motor aspects sometimes found in these patients.