A4. Interpreting Data on Cancer

Question 1

Interpreting the data on risk factors
Data on variation (the differences that exist between individuals) can be very tricky to interpret because some characteristics can be affected by many different genes (they’re polygenic) and many environmental factors. It’s difficult to know which factors (genes or environment) are having the greatest effect. This makes it hard to draw conclusions about the causes of variation.

What does the graph show?

Answer 1

This graph shows how the incidence of breast cancer is affected by both age and family history. There’s a positive correlation between incidence of breast cancer in women and the number of their first-degree relatives who have also had breast cancer.

The effect of family history decreases with age, but the incidence of breast cancer is always higher in women with a close family history of the disease. A woman is more likely to develop breast cancer if members of her family have had breast cancer, which suggests a genetic link.

Question 2

Preventing, treating and curing cancer

Cancer is caused by mutations in _____-______________and ________ ______________ ______. Understanding the role that these genes play in causing cancer, and knowing exactly how they work, can be really helpful for coming up with ways to prevent, treat and cure cancer.

Answer 2

Cancer is caused by mutations in proto-oncogenes and tumour suppressor genes. Understanding the role that these genes play in causing cancer, and knowing exactly how they work, can be really helpful for coming up with ways to prevent, treat and cure cancer.

Question 3

Preventing cancer

1. If a specific cancer-causing mutation is known, then it is possible to ______for (look for) the mutation in a person’s ____.

Example
It’s possible to screen for the mutated allele of BRCA1 (the tumour suppressor gene, which greatly increases a woman’s risk of developing breast cancer in her lifetime).

2. Knowing about this increased risk means that preventative steps can be taken to _______it.

Example
A woman with the BRCA1 mutation may choose to have a mastectomy (removal of one or both breasts) to significantly reduce the risk of breast cancer developing. Women with this mutation may also be screened for signs of breast cancer more often than the rest of the population, as early diagnosis increases the chances of recovery.

3. Knowing about specific mutations also means that more sensitive tests can be developed, which can lead to _______and _____ __________ ____________.

Examples

• There’s a mutation in the RAS proto-oncogene in around half of all bowel cancers. Bowel cancer can be detected early by looking for RAS mutations in the DNA of bowel cells.
• People with a mutated APC tumour suppressor gene have frequent colonoscopies to diagnose hereditary colon cancer earlier.

Answer 3

Preventing cancer

1. If a specific cancer-causing mutation is known, then it is possible to screen for (look for) the mutation in a person’s DNA.

Example
It’s possible to screen for the mutated allele of BRCA1 (the tumour suppressor gene, which greatly increases a woman’s risk of developing breast cancer in her lifetime).

2. Knowing about this increased risk means that preventative steps can be taken to reduce it.

Example
A woman with the BRCA1 mutation may choose to have a mastectomy (removal of one or both breasts) to significantly reduce the risk of breast cancer developing. Women with this mutation may also be screened for signs of breast cancer more often than the rest of the population, as early diagnosis increases the chances of recovery.

3. Knowing about specific mutations also means that more sensitive tests can be developed, which can lead to earlier and more accurate diagnoses.

Examples

• There’s a mutation in the RAS proto-oncogene in around half of all bowel cancers. Bowel cancer can be detected early by looking for RAS mutations in the DNA of bowel cells.
• People with a mutated APC tumour suppressor gene have frequent colonoscopies to diagnose hereditary colon cancer earlier.

Question 4

Treating and curing cancer

(3 points)

Answer 4

Treating and curing cancer

• The treatment for cancer can be different for different mutations, so knowing how specific mutations actually cause cancer can be very useful for developing drugs to effectively target them.
• Gene therapy (where faulty alleles in a person’s cells are replaced by working versions of those alleles) may also be able to treat cancer caused by some mutations.
• If you know that the cancer is being caused by inactivated tumour suppressor genes, it’s hoped that gene therapy could be used in the future to provide working versions of the genes.