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Colorectal Cancer (C18.9)

Over the past decade, mechanistic dissection of colorectal cancer (CRC) has evolved from a linear adenoma–carcinoma sequence model to a multidimensional systems view integrating genomics, epigenomics, tumor microenvironmental signaling, and immune contexture. Large-scale efforts such as The Cancer Genome Atlas have stratified CRC into molecular subsets characterized by canonical WNT/APC dysregulation, MAPK pathway activation (KRAS, NRAS, BRAF), PI3K–AKT signaling, TGF-β pathway alterations, and DNA mismatch repair deficiency (dMMR/MSI-H). This refined architecture has revealed druggable nodes including mutant BRAF V600E (targeted with BRAF/EGFR combinations), KRAS G12C (direct covalent inhibitors), HER2 amplification (dual HER2 blockade), and NTRK fusions (TRK inhibitors). Immune checkpoint blockade has transformed outcomes in dMMR/MSI-H disease via PD-1 axis inhibition, while resistance mechanisms—adaptive RTK feedback, pathway reactivation, and tumor–stroma crosstalk—are driving rational combination strategies. Emerging frontiers include targeting the WNT pathway via porcupine inhibitors, exploiting synthetic lethality in homologous recombination deficiency, modulating tumor metabolism, and leveraging bispecific antibodies and cellular therapies in microsatellite stable (MSS) tumors. Increasingly, CRC is being approached as a temporo-spatially dynamic signaling network rather than a static mutational catalog, enabling precision regimens that align therapeutic timing and pathway dependency with tumor state.

Causes

Colorectal cancer (CRC) arises through a multifactorial interplay of inherited susceptibility, acquired somatic mutations, environmental exposures, and chronic inflammatory signaling. Approximately 5–10% of cases are driven by high-penetrance germline syndromes such as Lynch syndrome (germline defects in MLH1, MSH2, MSH6, PMS2 leading to microsatellite instability) and Familial adenomatous polyposis (APC loss initiating constitutive WNT activation). The majority of CRC, however, is sporadic and reflects cumulative mutational burden influenced by aging, diet (high red/processed meat intake, low fiber), obesity, insulin resistance, alcohol consumption, and smoking. Chronic inflammatory states—particularly Ulcerative colitis and Crohn's disease—create a pro-tumorigenic microenvironment characterized by sustained NF-κB activation, oxidative stress, and cytokine-mediated epithelial proliferation. Epigenetic dysregulation, including CpG island methylator phenotype (CIMP), and microbiome alterations (e.g., enrichment of pro-oncogenic bacteria such as Fusobacterium nucleatum) further contribute to malignant transformation. Thus, CRC etiology reflects convergent genetic vulnerability and environmentally modulated inflammatory and metabolic stressors that progressively destabilize colonic epithelial homeostasis.

Pathophysiology

The pathophysiology of colorectal cancer (CRC) reflects stepwise disruption of epithelial homeostasis within the colonic crypt, driven by cumulative genetic and epigenetic alterations that reprogram proliferation, differentiation, apoptosis, and immune surveillance. In the canonical adenoma–carcinoma sequence, early loss of APC function results in constitutive WNT/β-catenin signaling, expansion of stem-like progenitor populations, and crypt hyperplasia. Subsequent activation of MAPK signaling through KRAS or BRAF mutations amplifies proliferative drive, while PI3K–AKT pathway engagement enhances survival and metabolic adaptation. Loss of tumor suppressors such as TP53 and SMAD4 impairs genomic integrity and TGF-β–mediated growth inhibition, facilitating invasion and metastatic competence. Parallel to this chromosomal instability pathway, mismatch repair deficiency produces a hypermutated phenotype with high neoantigen load, altering tumor–immune dynamics. The tumor microenvironment further reinforces progression via cancer-associated fibroblasts, angiogenic signaling (VEGF axis), immune checkpoint engagement (PD-1/PD-L1), and metabolic reprogramming toward glycolysis and glutamine dependence. Collectively, CRC pathophysiology is not a static accumulation of mutations but a dynamically evolving signaling network in which epithelial intrinsic alterations and stromal–immune crosstalk cooperatively drive malignant transformation, local invasion, and distant dissemination—most commonly to the liver through portal venous spread.

Clinical features

Clinical presentation of colorectal cancer varies by tumor location, stage, and molecular phenotype. Right-sided (proximal) tumors often manifest insidiously with occult gastrointestinal bleeding, fatigue, and iron deficiency anemia, whereas left-sided (distal) lesions more commonly produce changes in bowel habits (new-onset constipation or diarrhea), hematochezia, tenesmus, or obstructive symptoms due to luminal narrowing. Rectal tumors may present with rectal bleeding, urgency, or a sensation of incomplete evacuation. Advanced disease can produce systemic features such as unintentional weight loss, anorexia, and fatigue. Metastatic spread most frequently involves the liver, leading to hepatomegaly, right upper quadrant discomfort, or abnormal liver function tests, and less commonly the lungs or peritoneum. Paraneoplastic phenomena are uncommon but may include hypercoagulability. Notably, early-stage disease is often asymptomatic, which underpins the critical importance of screening strategies to detect premalignant adenomas or early invasive lesions before clinical manifestation.

Diagnosis

Diagnosis of colorectal cancer (CRC) integrates structural visualization, histopathologic confirmation, and molecular characterization. Screening and diagnostic evaluation most commonly begin with colonoscopy, which allows direct visualization of mucosal lesions, polypectomy, and biopsy for definitive histology. Alternative detection modalities include fecal immunochemical testing (FIT), multitarget stool DNA assays, CT colonography, and flexible sigmoidoscopy, though positive noninvasive tests require confirmatory colonoscopy. Tissue diagnosis establishes adenocarcinoma in the majority of cases and enables grading and assessment of lymphovascular invasion. Staging is performed using contrast-enhanced CT of the chest, abdomen, and pelvis to evaluate regional nodal involvement and distant metastases—particularly hepatic spread—and rectal cancers additionally require pelvic MRI for local staging and circumferential resection margin assessment. Serum carcinoembryonic antigen (CEA) serves as a prognostic and surveillance biomarker rather than a primary diagnostic test. Increasingly, comprehensive molecular profiling—testing for mismatch repair deficiency (MMR/MSI status), KRAS/NRAS mutations, BRAF V600E, HER2 amplification, and NTRK fusions—has become standard at diagnosis of advanced disease, as these biomarkers directly inform therapeutic selection and prognostic stratification within a precision oncology framework.

Mechanism of action videos

Clinical trials

  • Phase I Trial of ZEN003694 (ZEN-3694) in Combination With Capecitabine in Patients With Solid Tumors
  • Cancer Moonshot Biobank Research Protocol
  • A Safety and Preliminary Efficacy Trial of Pembrolizumab (MK-3475) in Children With Recurrent, Progressive or Refractory Diffuse Intrinsic Pontine Glioma (DIPG), Non-Brainstem High-Grade Gliomas (NB-HGG), Ependymoma, Medulloblastoma or Hypermutated Brain Tumors
  • Early Phase II Exploratory, Open-Label, Non-Randomized Study of Neoadjuvant Dostarlimab Monotherapy in Participants With Untreated T3-4N0-2 or Stage III pMMR/MSS Resectable Colon Cancer
  • Lubiprostone Combined With Maintenance Therapy for Prevention of Postoperative Recurrence in Peritoneal Metastatic Colorectal Cancer, A Randomized Controlled Phase II Study
  • MATCH Treatment Subprotocol H: Phase II Study of Dabrafenib and Trametinib in Patients With Tumors With BRAF V600E or V600K Mutations (Excluding Melanoma, Thyroid Cancer, Colorectal Adenocarcinoma, and Non-Small Cell Lung Cancer)
  • A Phase 1 Study of 5-Fluorouracil in Combination With Abemaciclib in Metastatic, Refractory CRC
  • A Phase 2, Randomized, Open-Label Study Comparing Telisotuzumab Adizutecan (ABBV-400) Monotherapy to the Current Standard of Care in Subjects With Post Adjuvant ctDNA Positive Colorectal Cancer and No Radiographic Evidence of Disease (NED)
  • A Phase Ia/Ib Dose-Escalation and Dose-Expansion Study Evaluating the Safety, Pharmacokinetics, and Activity of GDC-6036 as a Single Agent and in Combination With Other Anti-cancer Therapies in Patients With Advanced or Metastatic Solid Tumors With a KRAS G12C Mutation
  • A Multicenter, Randomized Controlled Trial of Preoperative Sequential Short-course Radiation Therapy and Oxaliplatin-based Consolidation Chemotherapy for Locally Advanced Rectal Cancer
  • Coproducing Personalised Care in a Digital Age: Using the Adversity, Restoration and Compatibility (ARC) Framework to Inform the Co-design of a Digital Care Planning Tool for People With Colorectal Cancer.
  • Y90 Radioembolization as Neoadjuvant Therapy for Potentially Resectable Patients With Colorectal Liver Metastases: Immune Markers Evaluation, Impact on Circulating Tumor DNA and Personalized Dosimetry Approach
  • Diagnosis and Risk Assessment of Locally Advanced Rectal Cancer Using Co-registered Ultrasound and Photoacoustic Imaging
  • DART: Dual Anti-CTLA-4 and Anti-PD-1 Blockade in Rare Tumors
  • A Phase 1 Study of ZEN003694 (ZEN-3694) in Combination With Cetuximab and Encorafenib in Patients With Refractory BRAF V600E Metastatic Colorectal Cancer
  • Advanced Classification of Colon Tumors From CT Scans Using Deep Learning for Optimized Treatment Decision-making : a Multicenter Study
  • Phase 1/1B Study of DS-8201a in Combination With ATR Inhibition (AZD6738) in Advanced Solid Tumors With HER2 Expression (DASH Trial)
  • Phase 3 Multicenter, Randomized, Open-label, Active-controlled Study of Sotorasib, Panitumumab and FOLFIRI Versus FOLFIRI With or Without Bevacizumab-awwb for Treatment-naïve Subjects With Metastatic Colorectal Cancer With KRAS p.G12C Mutation (CodeBreaK 301)
  • Adaptation and Implementation of an Evidence-Based Patient Navigation Intervention for Adolescent and Young Adult Cancer Survivors
  • An Open-label, Randomized, Multi-Center Study to Evaluate the Efficacy and Safety of Induction Treatment With Melphalan/HDS Followed by Consolidation Treatment With Trifluridine-Tipiracil Plus Bevacizumab Versus Trifluridine-Tipiracil Plus Bevacizumab Alone in Patients With Refractory Metastatic Colorectal Cancer With Liver Dominant Disease
  • A Randomized Phase III Study of Immune Checkpoint Inhibition With Chemotherapy in Treatment-Naive Metastatic Anal Cancer Patients
  • Early Commencement of Adjuvant Chemotherapy for Stage III Colon Cancer: a Multicenter Randomized Trial
  • A Multi-site, Open-label, Phase II, Randomized, Controlled Trial to Compare the Efficacy of RO7198457 Versus Watchful Waiting in Resected, Stage II (High Risk) and Stage III Colorectal Cancer Patients Who Are ctDNA Positive Following Resection
  • A Phase 1B/2 Pan-Tumor, Open-Label Study To Evaluate The Efficacy And Safety Of Ifinatamab Deruxtecan (I-DXd) In Subjects With Recurrent Or Metastatic Solid Tumors (IDeate-PanTumor02)
  • A Phase 1 Trial of MK-3475 Plus Ziv-Aflibercept in Patients With Advanced Solid Tumors
  • A Randomized Controlled Trial of Needle Ablation With 3D Verification vs Surgical Resection of Colorectal Cancer Liver Metastases
  • Understanding the Human Papillomavirus Genotype Attribution and Disease Burden of Anal Cancer in China: A Multicenter Hospital-based Study
  • Risk-Adapted Therapy for HIV-Associated Anal Cancer
  • Evaluation of the Effectiveness of Managing Chemotherapy Side Effects Using ePRO and a Standardized Telenursing Program for Cancer Patients
  • A Dose-Escalation and Expansion Study of the Safety and Efficacy of XL092 in Combination With Immuno-Oncology Agents in Subjects With Unresectable Advanced or Metastatic Solid Tumors
  • Colorectal Cancer Legal and Administrative Burden Support: A Pilot Clinical Trial
  • Phase 1 Trial of ONC201 for Chemoprevention in Colorectal Cancer
  • A Phase 1/1b Study Evaluating the Safety, Tolerability, Pharmacokinetics, Pharmacodynamics, and Efficacy of AMG 410 Alone and in Combination With Other Agents in Participants With KRAS Altered Advanced or Metastatic Solid Tumors
  • A Phase 1 and Randomized Phase 2 Trial of Pidnarulex (CX-5461) and Cemiplimab (REGN2810) in Refractory Microsatellite Stable Colorectal Cancer
  • Phase 2 Study to Evaluate the Efficacy and Safety of TPST-1495 in Patients With Familial Adenomatous Polyposis (FAP)
  • The Vanguard Study: Testing a New Way to Screen for Cancer
  • A Randomized Phase III Study of Nivolumab After Combined Modality Therapy (CMT) in High Risk Anal Cancer
  • Vaginal DHEA for Women With Gynecologic and Gastrointestinal Cancer After Radiation
  • A Randomized, Double-Blind, Phase 3 Study of Standard-of-Care Chemotherapy and Bevacizumab With or Without INCA33890 in the First-Line Treatment of Metastatic Microsatellite Stable Colorectal Cancer
  • Molecular Analysis for Therapy Choice (MATCH)

Therapeutic area: Oncology