Chapter 26: Cancer Cells

Definition: Cancer is a disease characterized by uncontrolled cell proliferation, typically caused by genetic and epigenetic alterations that disrupt normal cell cycle, apoptosis, and differentiation mechanisms.
- Proliferation: Refers to cell division as well as the ability to invade and/or spread to other parts of the body.

Description: A cancer that originates from epithelial cells, which line surfaces and cavities of the body (e.g., skin, gastrointestinal tract, glands, respiratory tract).
Common Carcinomas: Include breast, lung, colon, and prostate cancers. These cancers are more common because epithelial cells frequently divide and are exposed to various environmental factors.

Description: A cancer that arises from mesenchymal tissues including bone, muscle, fat, cartilage, or connective tissue.
Characteristics: Less common than carcinomas but typically more aggressive due to their supportive roles in the body.

Description: A cancer originating from blood-forming tissues, especially the bone marrow, leading to uncontrolled production of abnormal white blood cells (WBCs).
Circulation: Abnormal WBCs circulate widely in the body.

Description: A cancer that arises from lymphocytes, including B cells, T cells, and natural killer cells, often forming solid tumors in lymph nodes or lymphoid organs.
Circulation: Unlike leukemia, lymphoma does not typically circulate widely in the bloodstream.

Definition: A general term for abnormal tissue growth due to uncontrolled cell division; can be benign or malignant.

**Characteristics:
- Non-cancerous
- Grow slowly
- Remain localized and do not invade surrounding tissue
- Do not metastasize (spread to distant sites)
- Can cause issues by compressing neighboring tissues.**

Characteristics:
- Cancerous in nature
- Invade surrounding tissues
- Capable of metastasizing
- Exhibit genomic instability
- Display uncontrolled proliferation.

History: In 1951, Henrietta Lacks underwent treatment for aggressive cervical cancer. A biopsy was taken without her consent, which later became the first successful immortalized human cell line due to its ability to divide indefinitely.
- Oncogenes Involved:
- E6: Degrades the tumor suppressor protein p53.
- E7: Inactivates checkpoint regulator Rb.
- The HeLa cell line's unique growth is attributed to HPV type 18 infection, which harbors these oncogenes.

Genetic Mutations:
- Activation of oncogenes
- Loss of tumor suppressor genes
- Defects in DNA repair mechanisms
Growth Signal Autonomy:
- Cancer cells can produce their own growth factors and overexpress growth factor receptors.
Resistance to Growth Inhibition:
- Loss of contact inhibition and insensitivity to anti-proliferative signals.
Avoidance of Apoptosis: Avoidance mechanisms allow cancer cells to evade programmed cell death processes.
Prevention of Telomere Shortening:
- Upregulation of hTERT gene (human telomerase reverse transcriptase) enables the rebuilding of telomeres at chromosome ends.
- Telomeres: Become too short as they shorten with time, leading to cell death in normal cells, while cancer cells with genetic changes can continue dividing indefinitely.

Definition: Process where new blood vessels are formed to supply nutrients to tumors.
- Mediators: Secretion of vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) fosters angiogenesis.
- Matrix Metalloproteinases (MMPs): These enzymes break down the extracellular matrix, creating space for tumor cells to invade.

Cadherins:
- Loss of cadherins leads to decreased cell adhesion and increased motility, which contributes to local invasion and eventual metastasis.
- Example: E-cadherin plays a crucial role in epithelial cancers.
Metastasis Process:
- Involves local invasion of the primary tumor, intravasation (entering blood or lymph), circulation through the body, extravasation (entering new tissues), and formation of secondary tumors.

Carcinogens: Substances that cause cancer. Evidence for carcinogenicity in humans varies from sufficient evidence to limited or no evidence.
- Types:
- Sufficient Evidence: e.g., tobacco smoking, solar radiation, alcoholic beverages, processed meats.
- Probably Carcinogenic: e.g., emissions from frying, red meat, night shift work.
- Possibly Carcinogenic: e.g., gasoline fumes, pickled vegetables, aloe vera extracts.

A biological test that evaluates the mutagenic potential of a chemical, indicating its potential carcinogenicity. The test uses a histidine-auxotrophic mutant of Salmonella that can grow only in the presence of histidine.
- Phrase: If reverse mutation occurs, it indicates that the chemical may cause mutations.

An initial event (e.g., exposure to a chemical carcinogen) that damages DNA in a single cell and creates a permanent mutation.

Stimulation of initiated cells to proliferate.
- If cell proliferation ceases before further mutations occur, the spread of cancer may be halted at this stage.

Accumulation of additional mutations leading to cells becoming more abnormal and aggressive, demonstrating hallmark signs of cancer like invasion and metastasis.

Methods include:
- Histopathological examination: Considered the gold standard.
- Imaging Techniques: CT, MRI, and PET scans.
- Genetic Testing: Searching for specific gene mutations.
- Physical Examinations.

Methods include:
- Mammography: For breast cancer
- Pap Smear and HPV Testing: For cervical cancer
- Colonoscopy: For colon cancer
- PSA Blood Test: For prostate cancer.