What you need to know
- Explain cancer as uncontrolled cell division caused by changes to control systems.
- Compare benign and malignant tumours.
- Explain invasion, spread through blood or lymph and secondary tumours.
- Describe genetic, lifestyle and environmental risk factors.
- Distinguish screening from diagnosis and compare broad treatments.
Loss of cell-cycle control
Normal cells divide only when signals and control points allow it. Mutations in genes involved in growth, DNA repair or cell death can remove these controls. A clone of abnormal cells may then divide repeatedly and form a tumour.
Cancer is not one disease. Different cancers begin in different cell types, have different mutations and respond differently to treatment.
A mass of abnormal cells produced by uncontrolled cell division.
Benign and malignant tumours
| Feature | Benign tumour | Malignant tumour |
|---|---|---|
| Growth | Usually slower and contained | Often faster and less controlled |
| Boundary | Often enclosed in a capsule | Invades surrounding tissues |
| Spread | Does not normally spread to distant sites | Cells can enter blood or lymph and spread |
| Effect | May compress organs or produce excess hormones | Damages tissues and can form secondary tumours |
Misconception AlertA benign tumour is always harmless.Select to reveal the correctionSelect to hide the correction
Benign tumours do not invade other tissues, but they can still cause serious damage by pressing on organs such as the brain.
Cancer risk factors
- Inherited alleles can increase susceptibility by affecting cell-cycle control or DNA repair.
- Tobacco smoke contains carcinogens that increase mutation risk.
- Ultraviolet and ionising radiation can damage DNA.
- Some infections increase risk by causing persistent cell damage or altering cell control.
- Alcohol, diet, obesity and occupational exposures are associated with particular cancers.
- Age matters because mutations accumulate and cell-control systems change over time.
Most cancers result from several interacting genetic and environmental changes rather than one event.
Screening and diagnosis
Screening tests people without symptoms to identify those more likely to have a disease or early abnormal change. It does not itself give a final diagnosis. A positive screening result usually leads to further imaging, laboratory tests or a biopsy.
Earlier detection can make treatment more effective, but screening can produce false positives, false negatives and detection of abnormalities that would never have caused harm. Screening programmes balance these outcomes against benefits for the target population.
Broad treatment principles
| Treatment | Principle | Limitation |
|---|---|---|
| Surgery | Removes a localised tumour and surrounding tissue. | May not remove cells that have spread and can damage healthy tissue. |
| Radiotherapy | Ionising radiation damages DNA in targeted cancer cells. | Can damage nearby healthy cells. |
| Chemotherapy | Drugs target rapidly dividing cells or particular cancer processes. | Can affect healthy dividing cells and cause side effects. |
| Targeted or immune treatment | Acts on particular molecular features or helps immunity attack cancer cells. | Only suitable for some cancers and resistance may develop. |
Treatments are often combined. Choice depends on cancer type, stage, location, molecular features and the patient's health and preferences.
Evaluating cancer risk data
Compare absolute risks, sample sizes and exposure levels. Check whether other risk factors were controlled and whether evidence is repeated. A dose-response pattern and a plausible mechanism strengthen a causal explanation, but observational studies cannot control every variable.
Do not write that a risk factor “causes cancer in everyone”. State that it increases the probability by increasing cell damage or mutation risk.
Quick retrieval check
1. What makes a tumour malignant?
2. What is metastasis?
3. Why is a positive screening test not a diagnosis?
4. Why can chemotherapy cause side effects?
Exam connection
Explain why a malignant tumour can become life-threatening even when the primary tumour is small.
Show the mark points
- Malignant cells can invade surrounding tissue.
- Cells may enter blood or lymph.
- They can spread to other organs and form secondary tumours.
- Secondary tumours disrupt the function of essential organs.