lecture 11- Cancer Cells

Cell Biology: Cancer Cells Overview

Introduction to Cancer Cells

• Cancer is a disease resulting from abnormal cell function.

• Central roles played by gene mutations and gene expression changes.

• Environmental agents and lifestyle factors are common causes of cancer.

Tumors

Types of Tumors

• Benign Tumors:

  • Grow in a local area.

  • Rarely dangerous.

• Malignant Tumors:

  • Capable of invading surrounding tissues.

  • Can spread to distant parts of the body (metastasis).

  • Any malignancy is termed cancer.

Cancer Terminology

• Carcinomas:

  • 90% of all cancers arise from epithelial cells.

• Sarcomas:

  • Originate from connective tissues (bones, muscles).

• Lymphomas and Leukemia:

  • Arise from blood and lymphatic cells.

• Gliomas:

  • Cancers of the brain and spinal cord.

• Adenoma:

  • A benign tumor of glandular tissue.

Cell Division and Differentiation

Tumor Growth

• A cancerous growth results from uncontrolled cell division.

• A mass of tissues is called a tumor (or neoplasm).

• The balance of cell division, differentiation, and death is crucial for growth.

Cell Differentiation

• Definition: Process where cells acquire specialized functions.

• As they specialize, cells lose the ability to divide.

Skin Cell Differentiation

• New skin cells replace aged cells shed from the surface.

• Generated by division in the basal layer:

  • One cell remains undifferentiated and continues to divide.

  • The other differentiates, moving towards the skin surface.

Disruption of Balance in Tumors

Cell Cycle Regulation

• In tumors, cell division becomes uncoupled from differentiation and death.

• Some divisions result in two cells capable of continuous division, leading to tumor growth.

Factors Leading to Cancer

• Defects in signaling pathways, cell cycle control, and apoptosis contribute.

• Cancer cells bypass normal growth signals causing uncontrolled proliferation.

Apoptosis and Cancer

Mechanism of Apoptosis

• Apoptosis: Programmed cell death, eliminating damaged cells.

• Some cancers arise from failure to undergo apoptosis, rather than increased division.

Spread of Cancer

Mechanisms of Spreading

• Benign Tumors:

  • Remain localized; easily removed.

• Malignant Tumors:

  • Dangerous due to uncontrolled growth and spread.

  • 90% of cancer deaths attributed to metastasis, not the primary tumor.

Dual Process of Metastasis

• Invasion: Tumor cells invade nearby tissues and access blood vessels.

• Transport: Cancer cells travel through the bloodstream to new sites.

• Establishment: Leave bloodstream to form new tumors in various organs.

Immune System Interaction with Cancer

Immune Surveillance and Evasion

• The immune system can detect and kill abnormal cells.

• Immune evasion strategies of cancer cells:

  • Downregulation of antigens, secretion of immunosuppressive substances, and recruitment of regulatory T cells.

Cancer Promotion by Inflammation

• Chronic inflammation can enhance cancer progression.

Carcinogenesis Factors

Causes of Cancer

• Common causes include:

  • Environmental agents, lifestyle factors, and DNA mutations.

DNA Damage Mechanisms

• Types of DNA modifications caused by carcinogens include crosslinking, alterations, and strand breaks.

Examples of Carcinogens

• Chemical Carcinogens:

  • Benzene, formaldehyde, asbestos.

• Physical Carcinogens:

  • UV light, X-rays.

• Biological Carcinogens:

  • Viruses such as HPV that can integrate into host DNA.

Cancer-Causing Genes

Oncogenes and Tumor Suppressor Genes

• Oncogenes:

  • Genes that induce cancer when mutated or overexpressed.

• Tumor Suppressor Genes:

  • Normal genes that inhibit cell proliferation; their inactivation can lead to cancer.

Mechanisms of Oncogene Activation

• Can be activated by mutations, amplifications, or translocations of proto-oncogenes.

Mutations in Cancer Genes

Key Mutant Genes

• p53 Tumor Suppressor Gene:

  • Most frequently mutated; involved in DNA damage responses and apoptosis.

• RB Tumor Suppressor Gene:

  • Disruption leads to uncontrolled cell proliferation.

Genetic Variants and Cancer Risk

• Inherited mutations in p53 increase the risk of various cancers, while BRCA1/BRCA2 link to breast and ovarian cancers.