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Colorectal cancer is the third most common cancer worldwide, and the proportion of individuals diagnosed under the age of 50 years, referred to as early-onset colorectal cancer (EOCRC), is increasing. The aim of this study was to evaluate how the demographic and clinical features of EOCR in northern Sweden and Finland have changed over time. All patient data were extracted from local hospital surgical department databases between 1995 and 2022. Two CRC cohorts, Study Cohort I (1995-2005) 1237 patients and Study Cohort II (2006-2022) 4526 patients, were compared for age, sex, disease stage, tumour grade, tumour location, and mismatch repair status. EOCRC patients comprised 7% of all CRCs in Study Cohort I and 4% in Study Cohort II. The mean ages were 42 and 43 years respectively, and 55% of patients were female. The vast part of EOCRC tumours were left-sided stage III-IV cancers. Most tumours (n = 204, 73%) were low grade, and 10% showed mismatch repair deficiency. No significant differences in demographic or tumour characteristics were seen over time. EOCRC in northern Sweden and Finland is characterised by advanced-stage, low tumour grade, a slight female predominance, and stable clinical and pathological features. These findings partly contrast with reports on EOCRC from other high-income countries, highlighting the need for further research on advanced molecular characteristics and potential gender differences in incidence and survival of this population.

Recent studies have revealed that the long-recognized link between the historically defined Fusobacterium nucleatum group and colorectal cancer is largely driven by Fusobacterium animalis. This species, along with two others (Fusobacterium polymorphum and Fusobacterium vincentii), was recently reclassified as distinct from F. nucleatum, highlighting functional divergence within this group. Due to their close genetic relatedness, traditional partial 16S rRNA gene sequencing lacks the resolution to reliably distinguish these species. Nevertheless, accurate species-level identification remains essential in cancer-associated microbiome research. Here, we demonstrate that full-length 16S rRNA sequencing using Oxford Nanopore Technology, combined with a novel custom demultiplexing software, enables robust species-level discrimination within the Fusobacterium genus. Our approach accurately classified clinically relevant Fusobacterium species and recovered their expected proportions from whole cells, DNA mixtures, and clinical CRC specimens. This method provides high-resolution profiling to elucidate species-specific roles of Fusobacterium in colorectal cancer.

Background/Aim: Deficient mismatch repair (dMMR) colorectal cancer (CRC) arises from either sporadic epigenetic changes or hereditary Lynch syndrome. This retrospective multicenter cohort study is the first to evaluate the differences in risk for dMMR non-colorectal malignancy between patients with sporadic CRC and those with Lynch syndrome-associated CRC.

Patients and Methods: A cohort of 1,753 patients treated between 1996 and 2019 in Sweden, Finland, and the Czech Republic was evaluated for MMR status by immunohistochemistry and classified as either proficient (pMMR) or dMMR. The last one underwent BRAF V600E and MLH1 methylation testing to classify sporadic versus Lynch-associated cases. Non-CRC malignancies occurring within ±20 years of CRC diagnosis were identified via national cancer registries and medical records. Incidence rate ratios (IRRs) were estimated using Poisson regression adjusted for age, sex, tumor site, and stage.

Results: Among 277 dMMR cases (186 sporadic, 91 Lynch), 101 patients (36%) developed at least one non-CRC malignancy. Sporadic dMMR was associated with significantly lower risk compared to Lynch-associated dMMR [multivariable IRR=0.82; 95% confidence interval (CI)=0.51-0.91; p=0.014]. The reduced risk was consistent for malignancies occurring both before (IRR=0.48; p=0.047) and after CRC diagnosis (IRR=0.37; p=0.026). Age was an independent predictor of risk.

Conclusion: Sporadic dMMR CRC confers a substantially lower risk of non-colorectal malignancy than Lynch syndrome-associated CRC. These findings underscore the importance of incorporating MMR etiology into personalized surveillance strategies.

Colorectal cancer (CRC) represents a major global disease burden with nearly 1 million cancer-related deaths annually. TNM staging has served as the foundation for predicting patient prognosis, despite variation across staging groups. The consensus molecular subtype (CMS) is a transcriptome-based system classifying CRC tumors into four subtypes with different characteristics: CMS1 (immune), CMS2 (canonical), CMS3 (metabolic), and CMS4 (mesenchymal). Transcriptomics is too complex and expensive for clinical implementation; therefore, an immunohistochemical method is needed. The prognostic impact of the immunohistochemistry-based four CMS-like subtypes remains unclear. Due to the complexity and costs associated with transcriptomics, we developed an immunohistochemistry (IHC)-based method supported by convolutional neural networks (CNNs) to define subgroups that resemble CMS biological characteristics. Building on previous IHC-classifiers and incorporating β-catenin to refine differentiation between CMS2- and CMS3-like profiles, we categorized CRC tumors in a cohort of 538 patients. Classification was successful in 89.4% and 15.9% of tumors were classified as CMS1-like, 35.1% as CMS2-like, 38.7% as CMS3-like, and 11.7% as CMS4-like. CMS2-like patients exhibited the best overall survival (p = 0.018), including when local and metastasized disease were analyzed separately. Our method offers an accessible and clinically feasible CMS-inspired classification, although it does not serve as a replacement for transcriptomic CMS classification.

The recent introduction of immune checkpoint inhibitor therapy has significantly improved outcomes for patients with colorectal cancer (CRC). The most pronounced clinical benefits were observed in patients with immunogenic microsatellite instable (MSI)/deficient MMR (dMMR) tumors. However, emerging evidence indicates that a subset of patients with microsatellite stable tumors may also respond to therapy. Finding predictive markers to identify these patients is critical. In this study, we analyzed the immunohistochemical expression of immune checkpoints CTLA-4, PD-1, and PD-L1 using multispectral imaging in 151 CRC patients with defined molecular characteristics. Consistent with prior reports, MSI tumors had higher levels of all immune checkpoints analyzed than microsatellite stable tumors. Notably, distinct patterns of immune checkpoint expression were associated with KRAS and BRAF mutation status. KRAS-mutated tumors showed lower, and BRAF-mutated tumors higher, expression of immune checkpoints compared to wild-type/wild-type tumors. The strongest association with KRAS and BRAF mutations was observed for PD-L1 expression. The relationship between PD-L1 and KRAS/BRAF-mutational status was validated in a second cohort of 527 CRC patients, finding the association for PD-L1 expression in both stroma and in tumor cells. Furthermore, the role of BRAF mutation on immunity in CRC was found to be partly independent of MSI status. The strongest prognostic role was found for PD-L1 in stroma, underscoring the clinical significance of this marker. In conclusion, our findings suggest that KRAS and BRAF mutations, alongside MSI, may serve as valuable biomarkers for identifying CRC patient subgroups likely to benefit from immune checkpoint blockade in CRC.

Background: The immune response has important clinical value in colorectal cancer (CRC) in both prognosis and response to immunotherapy. This study aims to explore tumour immune cell infiltration in relation to clinically well-established molecular markers of CRC.

Methods: Multiplex immunohistochemistry and multispectral imaging was used to evaluate tumour infiltration of cytotoxic T cells (CD8+), Th1 cells (T-bet+), T regulatory cells (FoxP3+), B cells (CD20+), and macrophages (CD68+) in a cohort of 257 CRC patients.

Results: We found the expected association between higher immune-cell infiltration and microsatellite instability. Also, whereas BRAF-mutated tumours displayed increased immune-cell infiltration compared to BRAF wild-type tumours, the opposite was seen for KRAS-mutated tumours, differences that were most prominent for cytotoxic T cells and Th1 cells. The opposing relationships of BRAF and KRAS mutations with tumour infiltration of cytotoxic T cells was validated in an independent cohort of 608 CRC patients. A positive prognostic importance of cytotoxic T cells was found in wild-type as well as KRAS and BRAF-mutated CRCs in both cohorts.

Conclusion: A combined evaluation of MSI status, KRAS and BRAF mutational status, and immune infiltration (cytotoxic T cells) may provide important insights to prognosis and response to immunotherapy in CRC.

Background: Mounting evidence suggests a significant role of the gut microbiota in the development and progression of colorectal cancer (CRC). In particular, an over-representation of oral pathogens has been linked to CRC. The aim of this study was to further investigate the faecal microbial landscape of CRC patients, with a focus on the oral pathogens Parvimonas micra and Fusobacterium nucleatum.

Methods: In this study, 16S rRNA sequencing was conducted using faecal samples from CRC patients (n = 275) and controls without pathological findings (n = 95).

Results: We discovered a significant difference in microbial composition depending on tumour location and microsatellite instability (MSI) status, with P. micra, F. nucleatum, and Peptostreptococcus stomatis found to be more abundant in patients with MSI tumours. Moreover, P. micra and F. nucleatum were associated with a cluster of CRC-related bacteria including Bacteroides fragilis as well as with other oral pathogens such as P. stomatis and various Porphyromonas species. This cluster was distinctly different in the control group, suggesting its potential linkage with CRC.

Conclusions: Our results suggest a similar distribution of several CRC-associated bacteria within CRC patients, underscoring the importance of considering the concomitant presence of bacterial species in studies investigating the mechanisms of CRC development and progression.

Colorectal cancer is caused by a sequence of somatic genomic alterations affecting driver genes in core cancer pathways1. Here, to understand the functional and prognostic impact of cancer-causing somatic mutations, we analysed the whole genomes and transcriptomes of 1,063 primary colorectal cancers in a population-based cohort with long-term follow-up. From the 96 mutated driver genes, 9 were not previously implicated in colorectal cancer and 24 had not been linked to any cancer. Two distinct patterns of pathway co-mutations were observed, timing analyses identified nine early and three late driver gene mutations, and several signatures of colorectal-cancer-specific mutational processes were identified. Mutations in WNT, EGFR and TGFβ pathway genes, the mitochondrial CYB gene and 3 regulatory elements along with 21 copy-number variations and the COSMIC SBS44 signature correlated with survival. Gene expression classification yielded five prognostic subtypes with distinct molecular features, in part explained by underlying genomic alterations. Microsatellite-instable tumours divided into two classes with different levels of hypoxia and infiltration of immune and stromal cells. To our knowledge, this study constitutes the largest integrated genome and transcriptome analysis of colorectal cancer, and interlinks mutations, gene expression and patient outcomes. The identification of prognostic mutations and expression subtypes can guide future efforts to individualize colorectal cancer therapy.

Background and Objectives: Disparities between tumors arising via different sporadic carcinogenetic pathways have not been studied systematically. This retrospective multicenter cohort study evaluated the differences in the risk for non-colorectal malignancy between sporadic colorectal cancer (CRC) patients from different DNA mismatch repair status.

Methods: A retrospective European multicenter cohort study including in total of 1706 CRC patients treated between 1996 and 2019 in three different countries. The proficiency (pMMR) or deficiency (dMMR) of mismatch repair was determined by immunohistochemistry. Cases were analyzed for tumor BRAFV600E mutation, and BRAF mutated tumors were further analyzed for hypermethylation status in the promoter region of MLH1 to distinguish between sporadic and hereditary cases. Swedish and Finish patients were matched with their respective National Cancer Registries. For the Czech cohort, thorough scrutiny of medical files was performed to identify any non-colorectal malignancy within 20 years before or after the diagnosis of CRC. Poisson regression analysis was performed to identify the incidence rates of non-colorectal malignancies. For validation purposes, standardized incidence ratios were calculated for the Swedish cases adjusted for age, year, and sex.

Results: Of the 1706 CRC patients included in the analysis, 819 were female [48%], median age at surgery was 67 years [interquartile range: 60–75], and sporadic dMMR was found in 188 patients (11%). Patients with sporadic dMMR CRC had a higher incidence rate ratio (IRR) for non-colorectal malignancy before and after diagnosis compared to patients with a pMMR tumor, in both uni- (IRR = 2.49, 95% confidence interval [CI] = 1.89–3.31, p = 0.003) and multivariable analysis (IRR = 2.24, 95% CI = 1.67–3.01, p = 0.004). This association applied whether or not the non-colorectal tumor developed before or after the diagnosis of CRC in both uni- (IRR = 1.91, 95% CI = 1.28–2.98, p = 0.004), (IRR = 2.45, 95% CI = 1.72–3.49, p = 0.004) and multivariable analysis (IRR = 1.67,95% CI = 1.05–2.65, p = 0.029), (IRR = 2.35, 95% CI = 1.63–3.42, p = 0.005), respectively.

Conclusion: In this retrospective European multicenter cohort study, patients with sporadic dMMR CRC had a higher risk for non-colorectal malignancy than those with pMMR CRC. These findings indicate the need for further studies to establish the need for and design of surveillance strategies for patients with dMMR CRC.

The systemic inflammatory response (SIR), defined as elevated levels of circulating C-reactive protein (CRP), is an important predictor of impaired survival in colorectal cancer. The aim of this study was to explore the prognostic role of SIR and its association with tumour mismatch repair status and the immune response. Immune activity profiles of mononuclear cells isolated from CRC tissues and blood in the U-CAN exploration cohort (n = 69), were analysed by flow cytometry. In the U-CAN validation cohort (n = 257), T-helper cells (T-bet⁺), cytotoxic T cells (CD8⁺), regulatory T cells (FoxP3⁺), B cells (CD20⁺), and macrophages (CD68⁺) were analysed by multispectral imaging. Microsatellite instability was determined using five mononucleotide-repeat microsatellite markers. Patients with high CRP levels (> 10 mg/l) were significantly more often diagnosed with high-grade tumours and tumours exhibiting microsatellite instability. However, some patients with high CRP levels were found to have microsatellite-stable tumours. Furthermore, high CRP levels were associated with specific tumour immune traits including an augmented macrophage response and were significantly linked to poorer cancer-specific survival, particularly in patients with microsatellite-stable tumours. In conclusion, our findings suggest an interplay between SIR and mismatch repair status in CRC prognosis which needs to be further explored.