Cancer: Causes, Types and Treatment Explained Simply

Cancer is a disease where some of the body's own cells lose control over division and keep multiplying when they should stop. These abnormal cells can form a lump called a tumour and may spread to other parts of the body. Cancer is not one disease but a group of over 100 related diseases.

Learning about cancer matters because early detection greatly improves survival, and many cancers are preventable through lifestyle choices. It also helps you understand why treatments like chemotherapy affect hair and blood cells — they target rapidly dividing cells.

Key Concepts

A benign tumour grows slowly, stays in one place, and does not spread. A malignant tumour is cancerous: cells invade nearby tissues and can metastasise. Metastasis means cancer cells break off, travel through blood or lymph, and form new tumours elsewhere.

Carcinogens are agents that cause cancer, such as tobacco smoke, ultraviolet radiation, and certain viruses. Proto-oncogenes are normal genes that promote cell division; when mutated they become oncogenes that drive uncontrolled growth. Tumour suppressor genes like p53 normally stop division of damaged cells; loss of their function removes the brakes.

• Carcinoma: cancer of epithelial cells (skin, lung, breast, colon).
• Sarcoma: cancer of connective tissue (bone, muscle, cartilage).
• Leukaemia: cancer of blood-forming cells, no solid tumour.
• Lymphoma: cancer of lymphoid tissue.

How It Works

1. DNA damage accumulates from carcinogens, replication errors, or inherited mutations.
2. Mutations activate oncogenes and inactivate tumour suppressors in the same cell lineage.
3. The cell ignores growth signals and avoids programmed cell death (apoptosis).
4. Repeated divisions create a mass; new blood vessels grow into it (angiogenesis).
5. Some cells gain ability to invade and metastasise, making treatment harder.

Worked Example

Consider lung cancer risk from smoking. A cigarette contains about 7,000 chemicals, at least 70 known carcinogens. If a person smokes 20 cigarettes per day for 30 years, that is 20 × 365 × 30 = 219,000 cigarettes. Each puff exposes bronchial epithelial cells to benzo[a]pyrene, which forms DNA adducts. Statistically, lifelong smokers have roughly 15-30 times higher lung cancer risk than non-smokers. Quitting reduces risk progressively: after 10 years, risk drops to about half that of a continuing smoker. This calculation shows why duration and dose both matter.

Common Misconceptions

• Misconception: Cancer is contagious. Correction: Cancer itself does not spread person to person; only some cancer-causing viruses (HPV, hepatitis B) can be transmitted.
• Misconception: A biopsy spreads cancer. Correction: Properly performed biopsies do not cause metastasis; they are essential for diagnosis.
• Misconception: All tumours are cancer. Correction: Benign tumours do not invade or metastasise, though they may need removal if they press on vital structures.

Real-World Applications

Screening programs — mammography for breast cancer, Pap smear for cervical cancer, colonoscopy for colon cancer — detect disease early. Treatments include surgery to remove tumours, radiotherapy using ionising radiation, chemotherapy with cytotoxic drugs, immunotherapy that boosts T cells, and targeted therapy like imatinib for chronic myeloid leukaemia. Prevention through tobacco control, HPV vaccination, sun protection, and healthy diet could prevent an estimated 30-50 percent of cancers according to the World Health Organization.

Cancer arises when mutations remove normal controls on cell division, leading to benign or malignant tumours, with metastasis marking the most dangerous stage. Knowing causes, types, and treatments helps in prevention, early detection, and understanding modern therapies.