Cancer: Overview and Cellular Basis

Definition and Characteristics

Cancer is a group of diseases characterized by the rapid and uncontrollable development and production of abnormal cells. These cells can invade surrounding tissues and may spread to other parts of the body (metastasis).

• Uncontrolled cell growth: Cancer cells bypass normal regulatory mechanisms of the cell cycle.

• Tumor formation: Accumulation of abnormal cells leads to the formation of masses called tumors.

• Metastasis: Cancer cells can travel to distant sites, forming secondary tumors.

• Example: Lung cancer, skin cancer, cervical cancer.

Cell Cycle and Regulation

Phases of the Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide. Proper regulation ensures healthy tissue growth and repair.

• G1 Phase: Cell grows and prepares for DNA replication.

• S Phase: DNA replication occurs.

• G2 Phase: Cell prepares for mitosis.

• M Phase: Mitosis (nuclear division) and cytokinesis (cytoplasmic division).

Equation:

• Example: Skin cells regularly undergo the cell cycle to replace dead cells.

Genetic Regulation of Cell Growth

Proto-oncogenes

Proto-oncogenes are normal genes that regulate cell growth and division. When functioning properly, they promote healthy cell proliferation.

• Definition: Genes that encode proteins involved in stimulating cell division.

• Activation: Proto-oncogenes are "off" in normal cells and become "on" when needed for growth.

• Mutation: When mutated, proto-oncogenes become oncogenes, leading to uncontrolled cell division.

• Example: The RAS gene family.

Tumor Suppressor Genes

Tumor suppressor genes normally function to prevent cell growth and division. They act as the "brakes" of the cell cycle.

• Definition: Genes that encode proteins inhibiting cell division or promoting apoptosis (programmed cell death).

• Loss of function: Mutations in these genes remove growth inhibition, allowing cells to divide uncontrollably.

• Example: TP53 (p53 protein), RB1 (retinoblastoma protein).

Oncogenes

Oncogenes are mutated forms of proto-oncogenes that drive uncontrolled cell division, contributing to cancer development.

• Definition: Genes that, when activated or overexpressed, cause cells to divide uncontrollably.

• Example: HER2 in breast cancer.

Development and Progression of Cancer

Stages of Cancer Development

Cancer develops through a series of genetic and environmental changes that disrupt normal cell regulation.

• Initiation: Mutation in DNA caused by carcinogens (chemical, physical, biological agents).

• Promotion: Chemical substances (promoters) stimulate the growth of mutated cells.

• Progression: Mutated cells divide uncontrollably, forming tumors and potentially metastasizing.

Types of Tumors

• Benign Tumor: Non-cancerous, does not invade surrounding tissues or metastasize.

• Malignant Tumor: Cancerous, invades nearby tissues and can spread to other parts of the body.

Risk Factors and Causes of Cancer

Genetic and Environmental Risk Factors

Multiple factors contribute to the risk of developing cancer, including genetic predisposition and exposure to carcinogens.

• Genetic risk: Inherited mutations (e.g., BRCA1 gene in breast cancer).

• Carcinogens: Substances that cause mutations leading to cancer.

Smoking and Alcohol

• Smoking: Leading cause of cancer; responsible for 85-90% of lung cancer deaths.

• Alcohol: Increases risk for cancers of the esophagus, liver, and others.

• Combined effect: Smoking and alcohol together greatly increase cancer risk.

Obesity and Lifestyle

• Obesity: Associated with increased risk of cancer, diabetes, cardiovascular disease, and hypertension.

• Lifestyle factors: Age, occupation, ethnicity, deprivation, and physical activity influence cancer risk.

Environmental Factors: Ozone and UV Radiation

Ozone Layer and UV Protection

The ozone layer screens out harmful ultraviolet (UV) radiation from the sun, protecting against skin cancer.

• Ozone depletion: Caused by chemicals like CFCs, increases UV exposure and skin cancer risk.

• UV types: UV-A, UV-B, UV-C (most harmful, mostly absorbed by ozone).

Skin Cancer and Melanoma

Types and Risk Factors

Skin cancer is one of the most common cancers, with melanoma being the most deadly due to its rapid metastasis.

• Risk factors: Fair skin, freckles, male gender, family history, chronic UV exposure, severe sunburns, unusual or numerous moles, weak immune system.

• Incidence: 1 in 5 Americans will develop skin cancer; South Carolina rate is 22.7 cases per 100,000 (same as national rate).

ABCDE's of Skin Cancer

• A: Asymmetry

• B: Border irregularity

• C: Color variation

• D: Diameter > 1/4 inch

• E: Evolving shape/size

Prevention, Testing, and Treatment

Prevention Strategies

• Know family history

• Regular medical screenings

• Self-exam techniques

• Avoid direct sunlight

• Maintain healthy diet and weight

• Do not smoke

• Drink alcohol in moderation

• Become educated about cancer risks

Testing Methods

• Genetic testing (e.g., BRCA1 gene)

• Biopsy

• Blood tests

• Imaging: X-rays, PET, MRI

• Visual and tactile observation

• Blood protein analysis for early-stage cancers

Treatment Options

• Surgery

• Radiation therapy

• Chemotherapy

• Vaccines (e.g., HPV vaccine for cervical cancer)

• Immunotherapy

• Homeopathy (alternative medicine; not evidence-based)

Special Topics: Cervical Cancer and HPV

Cervical Cancer and Chromosomal Changes

• Associated with chromosomal abnormalities (e.g., extra copies of chromosomes 6, 8, 12, 17).

• Cells used for research: Polio vaccine, AIDS, radiation effects, toxic substances, gene mapping.

Human Papilloma Virus (HPV) and Vaccination

• HPV is a major cause of cervical cancer.

• Gardasil vaccine prevents HPV infection and reduces cervical cancer risk.

• Controversies: Claims of side effects and behavioral changes have been refuted by major medical organizations.

Summary Table: Key Genes in Cancer

Additional info: Some context and definitions were expanded for clarity and completeness, including the cell cycle phases, gene functions, and prevention strategies.