colon cancer

Overview of Colorectal Cancer (CRC)

  • Colorectal Cancer (CRC): Most common in the lining of the large bowel, primarily arising from polyps.

  • Significance: Second leading cause of cancer-related deaths in Australia, with approximately 3,999 fatalities annually.

  • Early Detection: Over 90% survival rate over 5 years if diagnosed early.

Cancer Development and Characteristics

Multi-step Process

  • Cancer Development: Driven by mutation accumulation over time.

    • Tumor Development: Begins with benign adenoma progressing to malignant adenocarcinoma.

    • Tumors: Defined as clusters of abnormal cells growing faster than normal cells.

Tumor Types

  • Benign Tumors: Clustered cells with similar characteristics to originating tissue, generally non-invasive.

  • Malignant Tumors: Have the ability to invade surrounding tissues and metastasize.

Hallmarks of Cancer

Phenotypic Changes in Tumor Cells

  • Distinguishing Features:

    • Loss of contact inhibition.

    • Production of their own growth factors.

    • Survival without contact.

Genetic Mutations and Accumulation

  • DNA Mutations: Inevitable over a lifetime, due to a high number of cell divisions (approximately 10^16) and spontaneous mutation rates (10^10 mutations per gene).

  • Multiple Rounds of Mutation: Required for progression to cancer, with natural selection favoring the most malignant clones.

Types of Mutations

DNA Damage Pathways

  • Causes of Mutations:

    • Radiation/UV damage, chemical carcinogens (e.g., smoking), stress (reactive oxygen species), pathogens (e.g., viruses), and inherited mutations.

Changes in DNA and Their Effects

  1. Missense Mutation: Alters an amino acid, potentially changing protein function.

  2. Nonsense Mutation: Alters a stop codon, truncating the protein.

  3. Frameshift Mutation: Changes coding sequences by adding or removing bases.

  4. Gene Deletion or Amplification: Changes in protein function or overexpression (e.g., growth factors).

  5. Chromosomal Translocations: Formation of fusion proteins or oncogenes under strong promoters.

Genetic Instability and Cancer

  • Optimal Genetic Instability: Required for cancer development; promotes mutation accumulation, leading to functional impairments.

  • Somatic vs Germline Mutations:

    • Somatic mutations (non-heritable) vs. germline mutations (heritable) are pivotal in cancer progression.

Major Mutational Syndromes

  1. Familial Adenomatous Polyposis (FAP): Characterized by numerous polyps and a high likelihood of cancer if untreated (APC gene mutation).

  2. Hereditary Non-polyposis Colon Cancer (HNPCC/Lynch Syndrome): Associated with mismatch repair gene defects, results in high cancer risk, particularly in the right colon.

Pathways Leading to Colon Cancer

Key Genes and Pathways

  • APC, K-ras, P53, SMAD4: Mutations in these genes lead to tumor development and progression.

Mismatch Repair System

  • Function: Detects and repairs DNA errors. Deficiencies lead to microsatellite instability (MSI), contributing to colorectal cancer.

Tyrosine Kinase Signaling

  • Role in Cancer: Mutations activate signaling pathways that promote cell proliferation and inhibit apoptosis.

  • Key Players: Proto-oncogenes (e.g., Ras) and tumor suppressor genes (e.g., PTEN).

Metastasis

  • Mechanism: Involves changes in cancer cells that allow them to migrate from the primary tumor site through the lymphatic system to establish secondary tumors.

    • Epithelial to Mesenchymal Transition (EMT): Required for movement and invasion during metastasis.

    • Loss of E-cadherin: Contributes to cell detachment and migration, facilitating metastasis.

Summary of Colon Cancer Mechanisms

  • Progression: Cancer develops through successive mutations and genetic instability, leading to various modifications in cellular behavior and characteristics, fundamentally altering cell functions.