The Links Between Genes, DNA and Cancer
We now understand the links between DNA and cancer. Here we examine the scientific and medical advances and also consider the issue of cancer and home testing.
How Does Damaged DNA Lead To Cancer?
The link between damaged DNA and cancer was first made in the 1950’s and 60’s at the Institute of Cancer Research. The discovery was made by looking at mustard gas which was known at the time to cause cancer. Research went on to show that it was chemical damage to DNA that caused cancer and not, as had been thought, damage to the proteins within cells. This was a major discovery in understanding cancer.
Cell Division and Mutations
Inside the cells in our body is a nucleus which contains 23 pairs of chromosomes, essentially strings of DNA. DNA contains all the instructions for the cell, its purpose, how to behave, when to grow and reproduce and when to die. When cells divide, mutations, or faults, can however occur. This can happen naturally or can be caused by our environment, smoking tobacco or ultraviolet radiation from the sun for example. It is also possible that you inherit faulty genes from your parents. Cells can sometimes repair the faults; they may self-destruct or your immune system may kill them. What leads to cancer is when the cell doesn’t repair, doesn’t die and starts to multiply out of control.
4 main types of genes are involved in cell division :
- Oncogenes
- Tumour suppressor genes
- DNA repair genes
- Self-destruction genes.
Most tumours have faulty copies of more than one of these.
Genes and Cell Division
Oncogenes are the genes that tell a cell when to multiply and divide. When they become damaged cells are instructed to permanently divide, thus allowing a cancer to grow. Tumour suppressor genes can stop cells from growing and dividing but if they have a mutation cells can multiply out of control, again causing the spread of cancer. Damage to the DNA repair gene can mean that a cell cannot repair itself and a cancer can form as a result. Damage to the self-destruction gene means that a faulty cell doesn’t die as it should but survives and become cancerous.
The Breast Cancer Gene
One of the best-known cancer genes is that which affects breast cancer in both men and women. It was always accepted that breast cancer was a cancer common in some families of different generations. In the 1990’s a team working in the US identified the BRCA1 gene by sequencing DNA from families who suffered from breast cancer and identified mutations that occurred.
Not all women however with breast cancer showed the BRACA 1 gene and in the 1990’s the BRAC2 gene was discovered. We now understand that mutations in the BRACA genes are associated with breast cancer, but also ovarian, fallopian tube, prostate, pancreatic, lung cancers and malignant melanomas.
Inherited Cancer Genes
Sometimes you can inherit a gene fault, putting you in danger of developing the cancer. You can be tested to see if you have gene faults for a number of different cancers including breast cancer, bowel cancer, ovarian cancer, womb cancer and prostate cancer. Tests are also available for rare gene faults that can cause kidney cancer, melanoma skin cancer, pancreatic cancer and thyroid cancer.
Genetic Testing For Cancer
There are usually two steps to genetic testing. Firstly, a relative with cancer has a diagnostic blood test to see if they have a cancer risk gene. If this is positive, then you can be asked to have a blood test. A blood test can be conducted at a genetic clinic once your GP is satisfied that your family history is strong enough to refer you. It can take up to 2 weeks for results to come through. This type of testing is called predictive genetic testing. It is predictive because it can tell you what your risks are of developing cancer, it doesn’t mean you are definitely going to get cancer. You could also consider a home DNA test for cancer.
Home DNA Tests and Cancer
Many home testing DNA kits will also offer you the chance to be screened for your potential risk of developing cancer. In many of these tests your genetic profile will be matched against the general population to assess your risk. Various mutations will be analysed. For example, we know that the BRCA1 mutation increases a woman’s risk of developing breast cancer by 81%. Some tests provide a very long list of cancers they test for. It is important to note that home DNA tests should not be used in place of cancer screening.
Home DNA or GP Referral?
Home DNA tests are simple and easy to use and that’s why they are so popular. Whichever route you choose to go down is up to you, but it is important to make a number of observations. Some home DNA tests may give you results that you do not fully understand, and they may not look at all the mutations that occur that can cause cancer. The advice is to always consult your GP first and seek his or her advice if you have a family history of cancer. Home DNA tests may have a role here but always seek medical advice first. It is important to note that if a home DNA test gives you a positive test for the BRCA gene you may have to have results confirmed in a clinical setting as many home DNA test providers do advise that their tests are not intended for diagnostic purposes. If you have a strong family history of cancer, we would advise a conversation with your GP.
What Are The Pros and Cons Of Having a Predictive Genetic Test?
The main advantages of predictive genetic tests is that if you test positive, you have a faulty gene, this means you could develop cancer. Knowing this means you can make lifestyle changes to try to minimise your risks of developing cancer. This could include reducing your weight, reducing your alcohol intake, changing your diet and exercising more. You could also receive regular screening and could also consider surgery to further reduce your risk.
The main disadvantage of genetic testing is that being told you have a risk of cancer can be very stressful and cause anxiety. Many people say they would rather not know. In addition, some genetic tests prove inconclusive.
Genetic Counselling
Your GP can offer you genetic counselling before you take a predictive genetic blood test. A genetic counsellor is qualified in cancer genetics and can help you understand the genetic test itself, the medical implications of a positive or negative result, your risk of passing a mutation on to future children and what to do if you receive an inconclusive test.
Insurance and Genetic Testing
Some people do worry that if they have a genetic test whether at home or via their GP it will affect their insurance. It is important to note that there is currently no law to prevent this. But the Association of British Insurers have agreed on how they will use the results. This is known as the Concordat and Moratorium on Genetics and Insurance. The agreement says that an insurer will not ask you to take a genetics test, they can however ask you for the results of any genetics testing you have had.
New Developments In Cancer Detection In The Blood
We are all aware that the sooner we diagnose cancer then the quicker a patient can start treatment and hopefully survive the disease. Cancer research UK use a blood test that can detect at the moment 8 different cancers in the blood.
This is done by using the blood test to detect the faulty DNA in the blood stream. Research suggests that as cancer cells die, they release their DNA into the blood. The challenge for researchers is that the blood also holds DNA from normal cells, so it is important to be able to differentiate between normal DNA and DNA which has come from cancer cells.
One of the discoveries that has helped in testing is that scientists believe that there are size differences between these different DNA sources. DNA from normal cells is generally 166 base pairs long, DNA from cancer cells tends to be between 90 and 150 base pairs. This size difference can therefore determine the presence of cancer.
Why Is DNA from Cancer Cells Shorter?
When a normal cell dies the DNA is broken up by a process called apoptosis, this is a blueprint for how the DNA will be broken down. Normal cells will all follow this blueprint, producing 166 base pairs. But in a cancer cell this breaking down doesn’t work in the same way. This knowledge is hugely important in allowing doctors to be able to detect cancer in the first place but also to be able to understand how you are responding to treatment. Scientists are particularly excited that having this knowledge will help them detect cancers which in the past have proven difficult to detect including brain cancer, pancreatic cancer, renal cancer and ovarian cancer.