Mutations in the genes involved in regulating the cell cycle can lead to uncontrolled cell division, which leads to the formation of tumours and cancers.
Benign vs Malignant
What you need to know (from the AQA specification)
What you need to know (from the AQA specification)
The main characteristics of benign and malignant tumours.
It’s important to note that not all tumours are malignant (cancerous); some are benign, which are non-cancerous.
The table below outlines the main differences between benign and malignant tumours.
| Feature | Benign tumours | Malignant tumours |
|---|---|---|
| Growth rate | Usually slow | Often rapid and uncontrolled |
| Cell differentiation | Cells are well differentiated (similar to normal cells) | Cells are poorly differentiated or undifferentiated |
| Metastasis | Do not spread to other parts of the body | Can spread via blood or lymph (metastasis) |
| Effect on body | Usually localised effects | Can affect multiple organs (systemic) |
| Recurrence after removal | Unlikely to return if fully removed | Likely to recur after treatment |
| Encapsulated (fibrous tissue) | Often enclosed in a capsule/fibrous tissue to help separate abnormal growth from rest of body | Not encapsulated, so can spread to other parts of body |
Tumour Suppressor Genes
What you need to know (from the AQA specification)
What you need to know (from the AQA specification)
- The role of the following in the development of tumours:
- tumour suppressor genes and oncogenes
- abnormal methylation of tumour suppressor genes and oncogenes
Normal (not mutated)
- Tumour suppressor genes normally regulate the cell cycle to prevent uncontrolled cell division.
- If DNA damage is severe, they can trigger apoptosis (programmed cell death).
Mutation
- A mutation in a tumour suppressor gene can change the amino acid sequence, so the protein produced is non-functional.
- Cell division is no longer controlled, so cells divide rapidly and uncontrollably, forming a tumour.
Hypermethylation
- Hypermethylation of tumour suppressor gene at promoter region, leads to inactivation of the tumour suppressor gene.
- As a result, the tumour suppressor protein is not produced and cell division is no longer properly controlled, increasing the risk of tumour formation.
- E.g. BRCA1 is a tumour suppressor gene and hypermethylation of its promoter is associated with the development of some breast cancers
Oncogenes
Normal (not mutated)
- Proto-oncogenes normally stimulate controlled cell division by producing proteins that promote progression through the cell cycle.
Mutation
- If a proto-oncogene becomes mutated, it becomes an oncogene that is permanently active.
- Mutated proto-oncogene = Oncogene
- This leads to uncontrolled cell division and tumour formation.
- E.g. HER2 (associated with some breast cancers) and RAS (associated with bladder and other cancers).
Hypomethylation
- In some cancers, hypomethylation can increase expression of growth-promoting genes, contributing to oncogene overactivity.
Oestrogen & Breast Cancer
What you need to know (from the AQA specification)
What you need to know (from the AQA specification)
- The role of the following in the development of tumours:
- increased oestrogen concentrations in the development of some breast cancers.
After menopause, the ovaries stop producing oestrogen, but fat cells (adipose tissue) in the breast can still produce it. This can lead to a high oestrogen concentration in breast tissue, especially in people with more body fat.
- High levels of oestrogen will increase binding to the oestrogen receptor, a transcription factor.
- This elevates the transcription of genes coding for proteins involved in cell division, leading to increased cell proliferation in breast tissue.
- Read more about the mechanism Oestrogen Receptor (TF)
How this topic is tested
This analysis is based on past paper data from 2017 to 2025. It is intended for interest only and is not predictive of what will appear in future papers.
- Tested in 6 of 9 years (2017–2025): 17 question parts worth 40 marks.
- 28th most-examined topic overall by marks, 3rd in Unit 8.
Marks by year
Most-tested spec points
- Evaluating Cancer Evidence & Treatment: tested in 7 parts (19 marks)
- Oncogenes, Tumour Suppressor Genes & Oestrogen: tested in 3 parts (9 marks)
- Benign & Malignant Tumours: tested in 2 parts (2 marks)
Also links to: Variable Number Tandem Repeats, Factors Affecting Rate of Reaction, Semi-Conservative Replication.
Maths and practical skills
- Percentages, ratios and fractions (MS 0.3): e.g. 2025 P2 Q8.4
- Logarithms and log scales (MS 2.5): e.g. 2019 P3 Q6.2
- Units and standard form (MS 0.2): e.g. 2018 P2 Q2.3
- Standard deviation and range (MS 1.10): e.g. 2019 P3 Q6.6
- Averages (MS 1.2): e.g. 2020 P3 Q5.1
- Probability (MS 1.4): e.g. 2020 P2 Q2.4
- Area, volume and surface area of shapes (MS 4.1): e.g. 2019 P3 Q6.5
- Evaluating results and conclusions (PS 2.3): e.g. 2019 P3 Q6.8
Exam Question Practice
The TP53 gene codes for a tumour suppressor protein called p53. Mutations in TP53 are found in about half of all human cancers.
Explain how a mutation in TP53 can lead to cancer.
(3 marks)
Hint
What changes in the DNA? What happens to the protein it codes for? What does a tumour suppressor protein normally do?
Mark Scheme
- A change in the base sequence of the DNA (1 mark)
- So the amino acid sequence of p53 changes, and its tertiary structure changes (1 mark)
- So p53 no longer slows cell division, and the cells divide rapidly and uncontrollably (1 mark)
Explanation (not marked): Normally, p53 slows the cell cycle when DNA is damaged, or makes damaged cells die. If p53 doesn’t work, cells with damaged DNA keep dividing.
Also accepted / rejected
Tips
- A mutation is a change in the DNA base sequence. It isn’t a change in RNA, or the same as methylation
- This changes the amino acid sequence, so the tumour suppressor protein’s tertiary structure changes
- So cell division becomes rapid and uncontrolled. Say “cell division”, not “growth”
The HER2 gene codes for a receptor protein in the cell-surface membrane. When a growth factor binds to this receptor, the receptor sends signals into the cell that stimulate cell division. In some breast cancers, a change in the HER2 gene has turned it into an oncogene.
Suggest and explain how a change in the HER2 gene can cause a tumour to develop.
(3 marks)
Hint
What exactly changes in the gene? What happens to the protein it codes for? How would that affect the signals to divide?
Mark Scheme
- A mutation in the HER2 gene changes its base sequence (1 mark)
- So the receptor protein has a different shape and sends signals even when no growth factor is bound, or more receptor protein is made, so more signals are sent (1 mark)
- So the cells divide rapidly and uncontrollably (by mitosis), forming a tumour (1 mark)
Explanation (not marked): Normally, the receptor only sends signals when a growth factor binds to it, so cell division is controlled. An oncogene keeps the signals coming.
Also accepted / rejected
Also accepted
- A named mutation, e.g. substitution or duplication (point 1)
- A change in the amino acid sequence of the receptor (point 2)
- “Mitosis can’t be controlled” (point 3)
Not accepted
- No receptor protein is made, or the protein is non-functional (point 2)
- “Meiosis” (point 3)
Tips
- Say it’s a mutation, a change in the base sequence of the gene, not an epigenetic change
- The receptor protein is changed, or more is made. Don’t say no protein or a non-functional protein is made
- This causes rapid, uncontrolled cell division (mitosis), which forms a tumour
- The amino acid sequence changes in the protein, not in the gene
Also accepted
Not accepted