Corinna Lang-Schwarz

Tumour‐infiltrating lymphocytes (TILs) are recognized as critical components of the colorectal cancer (CRC) immune microenvironment, demonstrating significant prognostic and predictive implications. However, a clear and widely accepted definition of colorectal TILs has not yet been established, and TILs are not systematically used as biomarkers in current oncology practice. This highlights the need for standardized assessment methods and a deeper understanding of the complex role of TILs in CRC, necessitating collaborative work to achieve clinical importance. This report, on behalf of the International Immuno‐Oncology Biomarker Working Group (ITWG), provides a comprehensive overview of TILs in CRC, including a TILs‐assessment method. It details their multifaceted role of TILs within the tumour microenvironment, details current and emerging methods for their assessment and reviews their prognostic and predictive importance. The report also explores the relationship of TILs to other established and emerging biomarkers in CRC. Emerging trends, including AI‐driven analysis for automated TIL quantification, and single‐cell and spatial technologies for in‐depth characterization of the tumour microenvironment (TME), are also highlighted. The report concludes with a discussion of future directions and the ongoing efforts of the ITWG to address the challenges and standardize and advance the clinical application of TIL assessment in CRC.

Zusammenfassung Infektiöse Kolitiden zeigen histologisch ein Spektrum von unauffällig bis hin zu ulzeröser Entzündung. Auch wenn die Diagnose häufig mikrobiologisch oder virologisch gestellt wird, kommt der Histologie wegen des möglichen Zeit- und Kostenvorteils sowie der Differenzialdiagnostik und der damit verbundenen therapeutischen Konsequenzen (Antiinfektivum vs. Operation oder Immunsuppression) nach wie vor eine große Bedeutung zu. Pathologinnen und Pathologen spielen vor allem bei 3 diagnostischen Szenarien eine Rolle: 1) Die Erreger sind direkt lichtmikroskopisch sichtbar. 2) Entzündungsmuster weisen auf bestimmte Infektionen hin. 3) Das histologische Bild ist unspezifisch und muss gegen wichtige Differenzialdiagnosen abgrenzt werden, allen voran gegen die chronisch-entzündlichen Darmerkrankungen (CED). Dieser Beitrag bespricht Beispiele aus allen 3 Diagnosegruppen, ihre diagnostischen Kriterien und Differenzialdiagnosen.

Aims Special histomorphological subtypes of colorectal low-grade intraepithelial neoplasia (LGIN) with variable prognostic impact were recently described in patients with inflammatory bowel disease (IBD) referred to as non-conventional dysplasia. However, they can also be found in patients without IBD. We aimed to analyse the reproducibility, frequency and prognostic impact of non-conventional colorectal LGIN in patients with and without IBD. Methods Six pathologists evaluated 500 specimens of five different LGIN-cohorts from patients with and without IBD. Non-conventional LGIN included hypermucinous, goblet cell-deficient, Paneth cell-rich and crypt cell dysplasia. A goblet cell-rich type and non-conventional LGIN, not otherwise specified were added. Results were compared with the original expert-consented diagnosis from archived pathology records. Results Four or more pathologists agreed in 86.0% of all cases. Non-conventional LGIN was seen in 44.4%, more frequently in patients with IBD (52%; non-IBD: 39.3%, p=0.005). In patients with IBD non-conventional LGIN associated with more frequent and earlier LGIN relapse (p=0.006, p=0.025), high-grade intraepithelial neoplasia (p=0.003), larger lesion size (p=0.001), non-polypoid lesions (p=0.019) and additional risk factors (p=0.034). Results were highly comparable with expert-consented diagnoses. In patients without IBD, non-conventional LGIN may indicate a higher risk for concurrent or subsequent colorectal carcinoma (CRC, p=0.056 and p=0.061, respectively). Frequencies and association with high-grade intraepithelial neoplasia or CRC varied between the different LGIN subtypes. Conclusions Non-conventional histomorphology in colorectal LGIN is frequent and highly reproducible. Our results indicate an increased risk for CRC in patients with non-conventional LGIN, probably independent of IBD. We recommend reporting non-conventional LGIN in routine pathology reports.

The tumor–stroma ratio (TSR) has been repeatedly shown to be a prognostic factor for survival prediction of different cancer types. However, an objective and reliable determination of the tumor–stroma ratio remains challenging. We present an easily adaptable deep learning model for accurately segmenting tumor regions in hematoxylin and eosin (H&E)-stained whole slide images (WSIs) of colon cancer patients into five distinct classes (tumor, stroma, necrosis, mucus, and background). The tumor–stroma ratio can be determined in the presence of necrotic or mucinous areas. We employ a few-shot model, eventually aiming for the easy adaptability of our approach to related segmentation tasks or other primaries, and compare the results to a well-established state-of-the art approach (U-Net). Both models achieve similar results with an overall accuracy of 86.5% and 86.7%, respectively, indicating that the adaptability does not lead to a significant decrease in accuracy. Moreover, we comprehensively compare with TSR estimates of human observers and examine in detail discrepancies and inter-rater reliability. Adding a second survey for segmentation quality on top of a first survey for TSR estimation, we found that TSR estimations of human observers are not as reliable a ground truth as previously thought.

Background/Aim: Crypt branching in inflammatory bowel diseases (IBD) was previously classified into symmetric (CSB) and asymmetric branching (CAB). We aimed to validate the inter-rater agreement of the assessment of crypt branching (also called crypt fission) in patients with Crohn’s disease (CD) and to elucidate its potential diagnostic impact. Patients and Methods: A total of 100 colon biopsies from patients with active CD were analyzed. Two cohorts of patients with ulcerative colitis (UC) and infectious colitis, respectively, served as controls (UC-controls/infectious controls). Three pathologists scored the total number of branching crypts (TBC) as well as the number of CSB and CAB. Results: Inter-rater agreement ranged from moderate to good for TBC and CAB in the study cohort. The study cohort showed significantly higher counts of TBC, CSB, and CAB than the infectious controls (p<0.001 for TBC, p=0.008 for CSB, and p<0.001 for CAB). Cases with CD showed more TBC and CAB compared to cases with UC (p=0.001 each). Conclusion: Inter-rater agreement for crypt branching is reliable in patients with CD. Crypt branching was shown to be an additional histologic feature to distinguish active CD from infectious colitis. Additionally, it could be helpful in the distinction between CD and UC.

Aims Studying crypt branching in ulcerative colitis (UC) and in infectious colitis (IC), we detected previously unreported crypt-associated anomalies (CAAs). The objective was to describe, illustrate and assess the frequency of CAAs in inflamed colon mucosa in patients with UC and IC. Methods Sections from 100 consecutive biopsies with UC, in 50 with IC and in 27 with UC in remission (UCR) were reviewed. The following CAAs were identified: crypt eosinophilia, intracryptal epithelial hyperplasia, intracryptal epithelial budding, intracryptal supernumerary crypts, intracryptal epithelial bridges, crypt rings in rows and off-centre epithelial budding. Results The frequency of crypts with extensive crypt eosinophilia and with intracryptal epithelial budding was significantly higher in UC than in IC and UCR (pConclusions CAAs were found interspersed with branching crypts. CAAs persisted in long-lasting UC mucosal inflammation, but declined when the inflammation waned. Since similar anomalies are not present in normal colon mucosa, the results suggest that CAAs had been boosted by the ongoing mucosal inflammation. The development of these previously unreported CAAs in the colon mucosa with inflammation might embody pathological aberrations of cryptogenesis.

Background/Aim: This study aimed to validate the inter-rater agreement of the assessment of crypt branching (also called crypt fission) in patients with ulcerative colitis (UC) and to elucidate its potential diagnostic and prognostic impact. Patients and Methods: A total of 100 biopsies from patients with UC were analyzed. Two cohorts of 50 patients each served as controls [infectious controls/controls with low grade intraepithelial neoplasia (LGIN) in UC alio loco]. Three pathologists scored the number of total crypts in fission as well as the number of crypts in symmetric (CSF) and asymmetric fission (CAF). Results: Inter-rater agreement ranged from good to excellent in the study cohort. The number of crypts in fission correlated significantly with UC-activity (p=0.001; p<0.001). The study cohort showed higher mean counts of crypts in fission and significant more total and CAF than the infectious controls (p=0.007 and p=0.008), especially in male patients (p<0.001) The LGIN-control cohort showed significant more CSF (p=0.012). Conclusion: Inter-rater agreement for crypt branching was reliable in the study cohort. Crypt branching proved as an additional histologic feature to distinguish active UC against infectious colitis. Higher amounts of CSF may help identifying patients at higher risk for neoplasia.