Cancer

Question 1

What is cancer

Answer 1

A group of diseases caused by damage to the genes that regulate mitosis and the cell cycle.

Question 2

What are tumours

Answer 2

A group of abnormal cells

Question 3

What are cancerous tumours called

Answer 3

Malignant tumours

Question 4

What are non-cancerous tumours called

Answer 4

Benign

Question 5

Compare benign and malignant tumours

Answer 5

• Both can types can grow to a large size.
• Benign tumours grow very slowly whereas malignant tumours grow very rapidly.
• The nucleus of the cells in a benign tumour has a relatively normal appearance whereas the nucleus of the cells in a malignant tumour is often larger and appears darker due to an abundance of DNA.
• The cells in a benign tumour are often well differentiated (specialised) whereas the cells in a malignant tumour become de-differentiated (unspecialised).
• The cells of benign tumours produce adhesion molecules that make them stick together and so they remain in the tissue from which they arise (primary tumours). however, the cells of malignant tumours do not produce adhesion molecules and so they tend to spread to other regions of the body in a process called metastasis, forming secondary tumours.
• Benign tumours are surrounded by a capsule of dense tissue and so remain as a compact structure whereas malignant tumours are not surrounded by a capsule and so can grow finger-like projections into the surrounding tissue.
• Benign tumours are much less likely to be life threatening but can disrupt the functioning of a vital organ whereas malignant tumours are more likely to be life threatening as abnormal tumour tissue replaces normal tissue.
• benign tumours tend to have a localised effect on the body whereas malignant tumours often have systemic effects such as weight loss and fatigue.
• Benign tumours can usually be removed by surgery alone whereas the removal of malignant tumours usually involves radiotherapy/chemotherapy as well as surgery.
• benign tumours rarely reoccur after treatment whereas malignant tumours more frequently reoccur after treatment.

Question 6

What has DNA analysis of cancerous tumours told us

Answer 6

That cancer cells are derived from a single mutant cell.

Question 7

Briefly summarise how a cancerous tumour forms

Answer 7

• Cancer cells derive from a single mutant cell.
• The initial mutation causes uncontrolled mitosis of this cell.
• Later, a further mutation in one of the descendant cells leads to other changes that causes subsequent cells to be different from normal in growth and appearance.

Question 8

What are the two main types of gene that play a role in cancer

Answer 8

1) Tumour suppressor genes
2) Oncogenes

Question 9

What do proto-oncogenes do

Answer 9

• Stimulate a cell to divide when growth factors attach to a protein on its cell surface membrane.
• This then activates genes that cause DnA to replicate and the cell to divide.

Question 10

What are most oncogenes

Answer 10

Mutations of proto-oncogenes

Question 11

Describe how oncogenes can cause cancer

Answer 11

• If a proto-oncogene mutates into an oncogene it can become permanently activated for two reasons:
  1) The receptor protein on the cell-surface membrane can be permanently activated, so that cell division is switched on even in the absence of growth factors.
  2) The oncogene may code for a growth factor that is then produced in excessive amounts, again stimulating excess cell division.
• The result is that cells divide too rapidly or too out of control and a tumour/cancer develops.
• A few cancers are caused by inherited mutations of proto-oncogenes that cause the oncogene to be activated but most cancer-causing mutations involving oncogenes are acquired, not inherited.

Question 12

What is the purpose of tumour suppressor genes

Answer 12

• Tumour suppressor genes slow down cell division, repair mistakes in DNA, and are responsible for programmed cell death (apoptosis)
• They have the opposite role of proto-oncogenes
• A normal tumour suppressor gene maintains normal rates of cell division and and so prevents the formation of tumours.

Question 13

Describe the important difference between proto-oncogenes and tumour suppressor genes in causing cancer

Answer 13

Whilst oncogenes cause cancer by the activation of proto-oncogenes, tumour suppressor genes cause cancer when they are inactivated.

Question 14

Describe how tumour suppressor genes can cause cancer

Answer 14

• If a tumour suppressor gene becomes mutated, it is inactivated.
• As a result, it stops inhibiting cell division and cells can grow out of control.
• The mutated cells that are formed are usually structurally and functionally different from normal cells.
• While most of these die, those that survive can make clones of themselves and form tumours.
• There are a number of forms of tumour suppressor genes including TP53, BRCA1 and BRCA2.

Question 15

Describe how the tumour suppressor gene TP53 can cause cancer

Answer 15

• Some cancers are caused by inherited mutations of tumour suppressor genes but most are acquired, not inherited.
• For example, more than half of human cancers display abnormalities of the TP53 gene which codes for the p53 protein.
• Acquired mutations of the TP53 gene occur in many cancers, including lung and breast cancer.
• The p53 protein is involved in apoptosis which is activated when a cell is unable to repair DNA.
• If the gene for p53 is not functioning properly, cells with damaged DNA continue to divide which leads to cancer.

Question 16

What is hypermethylation

Answer 16

Increased DNA methylation

Question 17

What is the most common abnormality in DNA methylation that can lead to cancer

Answer 17

Hypermethylation

Question 18

Describe how hypermethylation can cause cancer

Answer 18

• Hypermethylation occurs in a specific region (promoter region) of tumour suppressor genes.
• This leads to the tumour suppressor gene being inactivated.
• As a result, transcription of the promoter regions of tumour suppressor genes is inhibited.
• The tumour suppressor gene is silenced
• As the tumour suppressor gene normally slows the rate of cell division, its inactivation leads to increased cell division and the formation of a tumour.

Question 19

Give a real example of when hypermethylation causes cancer

Answer 19

Hypermethylation is thought to occur in a tumour suppressor gene known as BRCA1 and leads to the development of breast cancer.

Question 20

What is the other type of methylation abnormality (not hypermethylation) that is thought to cause cancer

Answer 20

• Hypomethylation (reduced methylation).
• This has been found to occur in oncogenes where it leads to their activation and hence the formation of tumours.

Question 21

What hormonal process do oestrogens play a central role in

Answer 21

Regulating the menstrual cycle of women

Question 22

What is the link between the menopause and breast cancer and what is thought to cause it

Answer 22

After the menopause, a woman’s chance of getting breast cancer increases. This is thought to be due to increased oestrogen concentrations.

Question 23

What happens to the amount of oestrogen a woman releases after the menopause

Answer 23

• The production of oestrogen from the ovaries diminishes after the menopause.
• The fat cells of the breast tend to produce more oestrogens after the menopause.

Question 24

Describe the link between oestrogen production and breast cancer in post menopausal women

Answer 24

• The fat cells of the breast tend to produce more oestrogens after the menopause.
• These locally produced oestrogens appear to trigger breast cancer in post menopausal women.
• Once a tumour has developed it further increases the oestrogen concentration which therefore leads to increased development of the tumour.
• It also appears that white blood cells that are drawn to the tumour increase oestrogen production.
• This leads to even greater development of the tumour.

Question 25

How does oestrogen cause a tumour to develop

Answer 25

• Oestrogen activates a gene by binding to a gene which which promotes transcription.
• If the gene that oestrogen acts on is one that controls cell division and growth, then it will be activated and its continued division could produce a tumour.
• It is known that oestrogen causes proto-oncogenes of cells in breast tissue to develop into oncogenes which leads to the development of a tumour.