Cancer Biology Overview

Benign Tumors

• Relatively harmless in terms of microscopic and macroscopic characteristics
• Remain localized and do not spread
• Easily managed with surgical removal
• Patients generally survive
• Can still cause significant morbidity and even death

Malignant Tumors

• Also known as cancers
• Can invade and destroy surrounding tissues
• Can spread to distant sites (metastasize)
• Often lead to death

Invasion & Metastasis

• Abnormal cancer cells proliferate and spread
• Invasion: Direct migration and penetration into surrounding tissues
• Metastasis: Cancer cells spread through the lymphatic system and blood vessels

Multistep Carcinogenesis

• Initiation: A carcinogen causes permanent DNA change
• Promotion: The initiated cell is stimulated to grow by a promoter. Examples include alcohol, high estrogen, dietary fat, etc.
• Progression & Malignancy: A pre-neoplastic cell acquires additional mutations leading to invasive cancer.

Metastasis

• Seed and soil hypothesis: Certain tumor cells have an affinity for specific organs based on the organ's environment. This explains why metastases occur in specific locations.

Metastasis Factors

• Vascularization: Primary tumors grow through the synthesis and secretion of pro-angiogenic factors.
• Invasion of the organ stroma: Cells enhance expression of enzymes like MMP9 to invade.
• Invasion of lymphatic or vascular channels: Cancer cells enter the circulatory system.
• Survival in circulation: Cells must survive the turbulence of blood flow and evade immune and non-immune mechanisms.
• Arrest in capillary beds: Cells stop in the capillaries of distant organs.
• Extravasation: Cells move out of the blood vessels into the distant organ.
• Survival and proliferation: Tumor cells need a compatible environment to survive and multiply.

Cancer Risk Factors

• Diet: High intake of red and processed meats, salted foods, and low consumption of fruits and vegetables increase cancer risks.
• Physical activity: Regular physical activity can reduce the risks of developing colon, breast, and endometrial cancers.
• Tobacco: Contains carcinogens that cause various types of cancer.
• Ionizing radiation: Man-made sources of radiation like radon, x-rays, and gamma rays can cause cancer. Exposure to UV radiation from the sun or tanning beds can lead to skin cancer.
• Workplace hazards: Exposure to certain chemicals or substances like asbestos can increase cancer risks.
• Infection: Infectious agents like viruses can cause changes in cells that increase the risk of cancer.

Hallmarks of Cancer

• Sustaining proliferative signaling: Tumors can proliferate without external stimuli.
• Evading growth suppressors: Cancer cells bypass normal growth-regulating mechanisms.
• Resisting cell death: Cancer cells avoid programmed cell death (apoptosis).
• Enabling replicative immortality: Cancer cells evade mechanisms that limit cell division.
• Inducing angiogenesis: Tumors create new blood vessels to supply nutrients and oxygen.
• Activating invasion and metastasis: Cancer cells spread to other parts of the body.
• Genome instability: Mutations accumulate rapidly, driving the development of cancer.
• Inflammation: Inflammation can promote cancer development.

Self-Sufficiency in Growth Signals

• Oncogenes: Mutations in proto-oncogenes convert them to oncogenes, which encode oncoproteins that promote cell growth.
• Growth factors: Cancer cells may secrete their own growth factors or induce other cells to produce them.

Tumor Markers

• Prostate-specific antigen (PSA): Prostate cancer
• Cancer antigen 125 (CA125): Ovarian cancer
• Alpha-fetoprotein (AFP): Liver and testicular cancer
• Carcinoembryonic antigen (CEA): Lung, stomach, colon, ovarian and breast
• Carbohydrate antigen 19-9 (CA19-9): Pancreatic, gallbladder, and stomach cancers

Molecular Diagnosis

• Polymerase Chain Reaction (PCR): Detects and amplifies specific DNA sequences associated with cancer.
• Fluorescence in situ hybridization (FISH): Detects genetic changes and chromosomal abnormalities.
• Gene sequencing: Identifies mutations and other genetic changes.
• Next-generation sequencing (NGS): Advanced method of reading DNA for rapid analysis of genetic changes.

Molecular Diagnosis Applications

• Diagnosis of malignancy
• Prognosis and behavior prediction
• Detection of minimal residual disease
• Diagnosis of hereditary predisposition to cancer
• Therapeutic decision-making

This quiz covers the fundamental distinctions between benign and malignant tumors, including characteristics of invasion and metastasis. Additionally, it explores multistep carcinogenesis and the progression of cancer from initiation to malignancy. Test your knowledge on these critical concepts in cancer biology.