Understanding Cancer: Molecular Basis and Cell Growth Control

Cancer: Molecular Basis and Tumor Characteristics

Tumor Types and Characteristics

Cancer involves molecular alterations that generate cells with a selective advantage. These can manifest as:

• Benign Tumors: Abnormal cells grouped into a single mass.
• Malignant Tumors: Abnormal cells with the ability to spread to surrounding and distant tissues. These tumors are considered carcinogenic.

Invasion and Spread

The ability of malignant cells to invade tissues far from the origin through the bloodstream or lymphatic vessels is called metastasis.

Cancer Classification by Tissue Origin

Cancers are classified based on their tissue of origin:

• Carcinoma: Originating from epithelial cells.
• Sarcomas: Originating from muscle or connective tissue cells.
• Cancers not derived from either are sometimes called leukemia.

Specific Tumor Examples

• Adenoma: Benign tumor of glandular epithelium.
• Adenocarcinoma: Malignant tumor of glandular epithelium.
• Another example pair is chondroma (benign) and chondrosarcoma (malignant).

Approximately 90% of cancers are squamous cell carcinomas.

Factors Influencing Malignant Transformation

Carcinogenesis and Mutagenesis Agents

Factors influencing the malignant transformation of cells are related to carcinogenesis mutagenesis. Agents are grouped into three classes:

1. Chemical agents
2. Ionizing radiation
3. Viruses

Key Properties of Cancerous Growth

The hallmarks of cancerous growth include the ability to:

1. Ignore internal and external signals that regulate cell proliferation.
2. Prevent apoptosis (programmed cell death).
3. Evade and avoid replicative senescence and differentiation.
4. Be genetically unstable.
5. Possess invasion capacity.
6. Exhibit the ability for metastasis.

Identified main environmental agents affecting cancer development that are avoidable include:

• Snuff smoke
• Human Papillomavirus (HPV)
• Hepatitis B virus (HBV)

Critical Genes in Cancer Development

Gene Classes

Critical genes identified and usually altered in human cancers contribute to the disease's formation and can be grouped into two broad classes:

Proto-Oncogenes

These encode a wide variety of proteins involved in controlling cell proliferation and differentiation, including growth factors, growth factor receptors, components of signal transduction pathways, and transcription factors.

Tumor Suppressor Genes

These genes negatively regulate cell growth. The loss or inactivation of tumor suppressor genes is associated with malignancy.

The Role of the p53 Gene

The oncogene is a gene whose protein is involved in malignant cell transformation. The gene p53 plays roles in cell division, apoptosis, and maintaining genetic stability. Normally found in small amounts, its quantity increases when DNA is damaged (for example) to limit the damage.

p53 Function

It works by:

• Inhibiting cell cycle progression.
• Facilitating DNA repair.
• Inducing apoptosis if the damage is irreversible.