This section is for anybody who is worried that cancer might run in their family. It is also for people who have been advised, or who have decided, to see a cancer genetics specialist or genetic counsellor. If you don't have at least two relatives with the same type of cancer on the same side of your family, the information in this section is probably not relevant to you.

My eight year old daughter has Down's syndrome. Does this mean she is more likely to get cancer as she gets older?

The risks of getting cancer are different for people with Down's syndrome, compared to the rest of the population.

There is one type of cancer which is definitely commoner in young people with Down's syndrome. This is a type of leukaemia called acute myeloid leukaemia (AML). The great majority of cases of AML in children with Down's syndrome develop before the age of 4 years old although occasionally older children and adolescents are affected. Overall somewhere between 1 in 50 to 1 in 100 children with Down's syndrome will get AML. Although AML is more common in children with Down's syndrome there is good evidence that they actually respond better to treatment than other children and are more likely to be cured.

For other types of leukaemia the frequency of acute lymphatic leukaemia (ALL) is similar in people with Down's syndrome to the rest of the population whereas both chronic myeloid leukaemia and chronic lymphatic leukaemia seem to be less common.

For other kinds of cancer it has been suggested that lymphomas and testicular cancer occur more often with Down's syndrome but the evidence for this is uncertain, so even if there is any increased risk it is very small.

The likelihood of developing other types of cancer does seem to be definitely reduced if you have Down's syndrome. This is most striking for breast cancer which is rare in women with Down's syndrome but affects more than 1 woman in 10 in the rest of the population.

Several of my family have had breast cancer. Is it safe for me to take HRT for menopausal symptoms?

If you are over 50 years of age, taking HRT for more than a year or two increases your risk of breast cancer. So, if you are over 50 years of age and have an increased risk of breast cancer because of your family history, it’s usually best to avoid HRT.

However, your doctor will take into account your individual circumstances when talking this over with you. Factors that can affect the balance between the risks and benefits of HRT include your age, how severe your menopausal symptoms are and your personal risk of osteoporosis (brittle bones). There are alternatives to HRT for managing menopausal symptoms, which your doctor can discuss with you.

If you have an early menopause, before you are 50 years of age, the benefits of HRT may outweigh the risks, even if you have a family history of breast cancer. This will depend on all the factors mentioned above, so it’s best to talk things over with your specialist.

When a woman with a family history of breast cancer takes HRT her doctor will usually prescribe as low a dose as possible for as short a time as possible.

HRT that contains only oestrogen increases the risk of breast cancer less than ‘combined HRT’, which also contains progesterone. So, oestrogen only HRT is preferred where possible. Oestrogen only HRT can affect the lining of the womb so is usually only prescribed for women who have had their womb removed.

Breast cancer is a common cancer. So, although you have a family history of breast cancer this may be due to chance rather than a faulty gene. If your GP thinks you may have an increased risk of breast cancer they can refer you to a cancer genetics clinic or a specialist breast clinic, where you would be given advice about your risk of breast cancer and the risks and benefits of HRT in your situation.

The National Institute for Clinical Excellence (NICE) is a government body that gives advice and information on treatments within the NHS in England and Wales. NICE have produced information for women with breast cancer in the family.

Reference

McIntosh A et al. 2004. Clinical guidelines and evidence review for the classification and care of women at risk of familial breast cancer.

I am Turkish and am aware that children can be born with conditions that are linked to the parents. If a parent has cancer, can the baby be born with cancer?

It is not possible for a parent to directly pass cancer on to their children. If a father has cancer when a child is first conceived, he cannot pass that cancer through his sperm. Similarly if a mother has cancer during her pregnancy that cancer cannot spread to her growing baby.

However, sometimes one, or occasionally both parents, may carry abnormal genes which may increase the risk of their child developing cancer in later life.

The genes are the tiny clusters of chemicals in all our cells which control how our bodies behave, and copies of these genes are passed on from parents to their children. We now know that a small number of cancers are caused by faulty genes which are passed down through families. For example, about 1 in 10 breast cancers is caused by a faulty gene, as are about 1 in 20 bowel cancers.

If you are are worried that your child might be at an increased risk of cancer because of your family history, you should talk to your doctor. Your GP will ask questions about the family history. If the GP also thinks that it is necessary, she or he will refer you to a genetic counsellor or a cancer specialist. This could be in a family cancer clinic or a cancer genetics clinic.

Does cancer run in families?

Cancer is a common disease with 1 in 3 people affected in their lifetime. For most people it is a disease of old age and occurs by chance. However, in some families certain cancers occur more often than in others. There could be at least two possible reasons for this.

The family may share lifestyle or environmental factors that increase their risk of cancer. Lifestyle factors that can influence your risk of cancer include smoking, diet, weight, and alcohol intake. So, for example, in a family where several members smoke there may be more cases of smoking related cancers such as lung cancer.

There may be a faulty gene in the family that increases their risk of cancer. Doctors call this an inherited predisposition to cancer.

Cancers linked to inheriting a faulty gene are rare. Experts think that only 5 to 10 cases of cancer out of every 100 (5-10%) occur because of this. It is only likely that there may be an inherited predisposition to cancer if:

there are two or more close blood relatives on the same side of the family with the same type of cancer
members of a family get cancer at a younger age (under 60 years)
a close relative has two types of cancer (not one that has spread)
certain cancers happen together in a family, for example breast and ovarian cancer or bowel and womb cancer.

If your family is like this, and you are worried about developing cancer, you might find it helpful to talk to your GP about it. They may refer you to a genetics clinic for further assessment.

What are genes?

Genes contain the biological information we inherit from our parents. They affect the way our bodies grow, work and look. Every cell (tiny building block) in our body contains this information.

Genes are arranged in chromosomes. We have 46 chromosomes made up of 23 pairs. In each pair one chromosome is inherited from our mother and one from our father.

Different genes have different functions. Some genes determine our eye colour, some our height and so on.

Genes are made up of deoxyribonucleic acid (DNA). DNA consists of four chemical substances (bases). Each base is identified by a letter: A, T, C and G. These four letters, repeated in different combinations in our genes, contain all the information our bodies need to function.

How can genes cause cancer?

Genes are stored in cells, the building blocks of our body. They carry the instructions cells need to work properly.

Genes control what we look like and how our bodies work. They organise repairs to damaged cells, and tell cells when to rest, grow and die.

The cells in our bodies are constantly dividing to make new cells. In this way old or damaged cells can be replaced. Our genes control this process. They make sure that our body makes the right number of cells to keep us healthy.

Genes can be damaged by things in our environment, like sunlight or smoking. Sometimes, when a cell divides to make a new cell, a mistake is made that damages the gene. When genes are damaged the information they carry may be changed. Scientists call these changes in the genes, mutations.

Cancer is more likely to develop when certain types of genes are damaged, such as genes that tell cells:

when to rest or stop growing
how to repair themselves.

Sometimes when this type of gene is damaged it becomes a ‘cancer gene’.

Cancer genes are not able to repair damage or to switch cells off. This means cells that contain these genes multiply in an uncontrolled way and eventually develop into a cancer.

Usually, several changes, or mutations, have to happen in genes before a cell becomes cancerous. The older we become the more chance we have of building up enough changes in our genes to develop cancer. This is why cancers tend to become more common as we get older.

Most of the time genetic mutations are caused by damage to our genes during our lifetime. These gene mutations can't be passed on to our children. Rarely, some people are born with a mutation in one of their genes. They have inherited it from their mother or father and may pass it on to their own children.

If you are born with a mutation in a type of gene that controls cell growth or repair you have already begun to accumulate the changes that can lead to cancer. This is why people with an inherited ‘cancer gene’ tend to develop cancer at a younger age than people who haven't inherited one. Inheriting a faulty gene doesn't mean that you will definitely get cancer but it means that you have a higher risk.

I have lots of cancer in my family. Am I likely to get it too?

Cancer isn't a single disease but a name for several hundred separate conditions each of which is different.

Cancer is also very common, about one in four of us will develop one or other form of cancer at some time during our lives.

These two facts mean that in most families there will be several relatives who have, or have had, some type of cancer. Usually this happens purely by chance and does not mean that the family is 'cancer prone' or that cancer runs in the family.

However, it is known that some types of cancer do occur more commonly in some families than others. There are at least two possible reasons for this. It could be due to some shared environmental factor (something in the diet or something else to do with a lifestyle common to a number of family members). Or it could be due to abnormalities in the genes, which are passed from one generation to another.

In recent years research has shown that a small minority (between 5 and 10 %) of several common forms of cancer, including breast cancer, cancer of the ovary and cancer of the bowel, are due to a defective gene. These genes can be passed from one generation to the next and so do account for some, but not all, of those families where these cancers are commoner than usual.
The abnormal genes do not themselves cause the cancer but they do mean that someone who has the faulty gene is more likely to develop cancer than someone who does not. So what is inherited is a greater risk of developing cancer and not the certainty that a cancer will develop. The degree of risk varies with different genes, with some it is quite small whilst with others it is very high indeed.

It is true to say, however, that for the great majority of cancers, including most breast, ovary and bowel cancers, there is no obvious family tendency and no evidence that they can be inherited. But our knowledge of cancer genetics is increasing, so we might understand the role of genes for other types of cancer in the future. So, if there is a history of the same cancer occurring in several family members, especially if they occurred at an early age, it is more likely that there will be an inherited increased risk of developing that type of cancer. If you have two or more cases of the same cancer on one side of your close family, you might want to tell your GP.

Can stomach cancer be inherited?

Most stomach cancers aren't hereditary and don't run in families. The exact cause of stomach cancer isn't known but we do know some risk factors for stomach cancer.

Occasionally, in some families stomach cancer is more common than average. This could be because risk factors such as diet are often shared in families. But, in some families it may be due to an inherited faulty gene. Sometimes called a 'cancer' gene

Having an inherited 'cancer' gene may mean that if a person gets stomach cancer it happens at a younger age than average. Most cases of stomach cancer are found in people over the age of 55. Only 1 in 100 cases of stomach cancer is diagnosed in someone under the age of 40. So if someone in your family develops stomach cancer in their 40s or younger this may need to be investigated.

One gene linked to bowel cancer called hereditary non polyposis colorectal cancer (HNPCC) can also increase the risk of stomach cancer. If a parent has HNPCC there is a 1 in 2 (50%) chance their child will inherit the gene. Only relatives who carry the gene are at increased risk of developing cancer.

Other genes that may increase the risk of stomach cancer include the FAP gene (familial adenomatous polyposis) and BRCA genes.

Some families with a strong history of stomach cancer do not have any recognised gene faults. In these families the increased number of cancers may be due to risk factors they share or, there may be a faulty gene, not yet discovered, in their family.

If you are worried that the risk of stomach cancer may be higher than normal in your family talk to your GP. They will be able to decide if any further action is needed.

The papers always seem to be full of stories about breast cancer. I am a 35 year old woman, and moved to the UK from Bangladesh with my parents 20 years ago. How likely am I to get breast cancer?

In the UK the figures show that breast cancer is the most common type of cancer in women. Overall about 1 in 9 women will develop breast cancer at some time during their life.

We don't fully understand all the reasons why women develop breast cancer. But, there are factors that are known to increase your risk. These are called risk factors for breast cancer.

Recent research has looked at whether the risk of breast cancer is different for women of South Asian origin (this includes anyone who was born in, or whose family came from, Bangladesh, India or Pakistan). The figures show that although breast cancer is still the most common type of cancer to affect South Asian women, the risk is about one third less than the average for other women in the UK. This means that the chance of a woman from a South Asian background developing breast cancer is about 1 in 14.

There is some evidence that these figures may be changing with time, and that for younger South Asian women, who were born and brought up in the UK, the level of risk may be increasing a little. This suggests that over several generations the risk may become the same in South Asian women as the rest of the UK population.

Which genes cause cancer of the ovary in families?

Most cases of ovarian cancer are not caused by inheriting faulty genes. They are sporadic cancers. This means they occur because of changes in genes that happen during a woman's lifetime.

Only a small number of women with ovarian cancer (about 5 -10%), have inherited a faulty ‘cancer gene’.

Inheriting a faulty gene doesn't mean you will definitely develop ovarian cancer. But, it does mean you have a higher risk.

On average the lifetime risk for a woman of developing ovarian cancer is about 1 in 70, about (1.5%). The risk for a woman who has inherited a faulty ‘cancer gene’ of developing ovarian cancer in her lifetime can be much higher than this. The degree of risk depends on the gene involved.

There are a number of genes linked to an increased risk of ovarian cancer. The most common are:

BRCA1 and BRCA2

These gene mutations cause an increased risk of both breast and ovarian cancer as well as an increased risk of some less common types of cancer.

If a woman has a BRCA1 mutation her risk of developing ovarian cancer may be as high as 1 in 2 (50%) over her lifetime.

A woman who has a BRCA2 mutation has a lifetime risk of ovarian cancer of about 1 in 4 (25%).

HNPCC (Hereditary Non-Polyposis Colorectal Cancer)

This is linked to a gene mutation which mainly increases the risk of bowel and womb cancers. But, it can also increase the risk of ovarian cancer.

Women with the HNPCC, mutation have a 1 in 10 risk of developing ovarian cancer in their lifetime.

In families with a faulty gene, only the women in the family who carry the faulty gene have an increased risk of ovarian cancer. Women who don't have the gene have the same risk of developing a cancer of the ovary as the rest of the population. A woman has a 1 in 2 (50%) chance of inheriting the faulty gene if one of her parents carries the gene mutation.

I have ovarian cancer and so did my mother. What are her chances my daughter will develop cancer of the ovary?

In the UK the risk of a woman developing cancer of the ovary before the age of 70 years is about 1 in 70 (about 1.5%). But some women have a higher risk that this because of a faulty gene that is passed on in their family.

Most cases of ovarian cancer are not caused by inheriting faulty genes. They are sporadic cancers. They occur because of changes in genes that happen during a woman's lifetime. Only a small number of women with ovarian cancer (5-10%), have inherited a faulty ‘cancer gene’.

Without testing it's not possible to say whether there is a faulty gene in your family or not. But, as both you and your mother have had ovarian cancer, your cancer specialist or family doctor can refer you to a Family Cancer Clinic, where a cancer genetics specialist will assess your risk. If the specialist thinks there may be an inherited gene fault in your family they will counsel you about genetic testing.

If you have a faulty gene there is a 1 in 2 (50%) chance your daughter has inherited it. Even if she has a faulty gene this doesn't mean she will definitely develop cancer, although her risk is increased. How great that risk is depends on which gene is involved. The genetic specialist will discuss this with you at the clinic.

What happens at a family cancer clinic?

A family cancer clinic can give advice to people who have a pattern of cancers in their family that might be the result of a faulty gene. At the moment family cancer clinics are usually only available at larger hospitals or regional centres, so you may have to travel some distance to get to one. You may also need to wait some time for an appointment.

Before your appointment the clinic may send you a questionnaire to fill in about your family history of cancer. When you go to the clinic a cancer genetics specialist will go through your family medical history with you. They will want to know about any family members who have had cancer and, if possible, the ages at which they developed cancer. The relatives that they will be most interested in are parents, grandparents, sisters, brothers, aunts, uncles, nieces, nephews, cousins and your children.

If the specialist feels there is a strong chance that you may have an inherited ‘cancer gene’ they will counsel you about genetic testing. Genetic testing looks for inherited faults in your genes which may increase your risk of cancer. It involves taking a small sample of blood from you. They will send this to a specialist laboratory to be tested. It can take several months before the results are available.

Of course, you don’t have to take up the offer of genetic testing. You might want to think it over, or talk to the genetic counsellor, your family or friends before you do.

Genetic testing is a two-step process.

The laboratory looks for the gene change (gene mutation) that might run in your family. This is the mutation search. The doctors need to test a member of the family who has cancer to find the gene change. A mutation search is a bit like trying to find a single spelling mistake in a big book. It involves reading the whole (or big parts of) the gene. This is why it can take a long time to do the test.
If the laboratory finds a gene mutation, the doctors will offer testing to other family members. We call this second test genetic screening or predictive testing. This second step is a lot easier. Once you have identified where a spelling mistake is in a book, you can easily check whether other books have the same mistake or not, because you know where to look.

Often the laboratory can’t find a mutation in any of the genes known to be involved in hereditary cancer, even when there is a strong family history of the disease. This doesn't mean that you aren't at increased risk of cancer. There are probably other genes involved in the development of cancer that scientists haven’t discovered yet and that they can’t test for. So, if there is a very strong family history of a certain cancer, doctors assume that members of the family are at increased risk even if genetic testing doesn’t find one of the known mutations.

If the doctors think that you and your relatives have a higher risk of cancer they will talk over with you ways in which this risk can be managed, such as screening.

Can you tell me about ovarian screening for women at high risk of developing ovarian cancer?

Women have an increased risk of developing ovarian cancer compared with the general population when they have:

A strong family history of ovarian (and sometimes breast or bowel) cancer and/or
An inherited gene change (gene mutation) associated with an increased risk of developing ovarian cancer.

If you are at higher risk you can be referred to a family cancer clinic. They will counsel you about your risk and discuss possible ways to manage it.

Ovarian screening

The aim of ovarian screening is to detect cancer at an early stage if it occurs. However, we still don’t know if screening is effective at detecting ovarian cancer early. So, it is only available as part of a research trial.

A large research study (UKFOCSS) is looking into whether screening for ovarian cancer is helpful for women who have a higher than average risk. The study involves regular blood tests and ultrasounds of the ovaries.

One of the problems with ovarian cancer screening is that it can produce ‘false positives’. A false positive means that a healthy person has a test result that wrongly suggests they have cancer. Because the test result is abnormal further tests to check for ovarian cancer are needed. These tests may involve surgery and can carry risks. So ovarian screening might expose you to risks even though there is nothing wrong with your ovaries.

If you are considering taking part in the UKFOCSS trial, because you have a strong family history of ovarian cancer, you can find more about ovarian cancer and about taking part in clinical trials on our website.

For some women, an alternative to ovarian screening is surgery to remove the ovaries. This is called risk reducing oophorectomy.

I am 45 years old and have breast cancer. My aunt has also had breast cancer. Is my daughter at risk?

In Britain the risk of a woman developing breast cancer during her lifetime (if she lives to 85 years of age) is about 1 in 9. This makes it the commonest type of cancer in women in Britain.

Most cases of breast cancer are not caused by inheriting faulty genes. They are sporadic cancers. They occur because of changes in genes that happen during a woman's lifetime. Only a small number of women with breast cancer (5-10%), have inherited a faulty ‘cancer gene’.

Without testing it's not possible to say whether there is a faulty gene in your family or not. But, as both you and your aunt have had breast cancer, your cancer specialist or family doctor can refer you to a Family Cancer Clinic, where a cancer genetics specialist will assess your risk. If the specialist thinks there may be an inherited gene fault in your family they will counsel you about genetic testing.

What can be done if a woman is at increased risk of developing breast cancer?

Being at increased risk of breast cancer means that there is a possibility you may develop the disease but doesn't mean that it will definitely happen.

You may have an increased risk of developing breast cancer if you have:

A strong family history of breast (and sometimes ovarian) cancer

and/or

An inherited gene change (gene mutation) associated with an increased risk of developing breast cancer.

A family cancer clinic can assess your risk of developing breast cancer and offer you counselling about possible ways to manage it.

The options for women thought to be at increased risk of breast cancer include:

screening, to detect cancer early if it occurs
surgery, to reduce the risk of developing breast cancer
taking part in a research trial to find if a drug can reduce the risk of breast cancer developing. Using drugs to reduce the risk of cancer is called chemoprevention.

Screening

This may involve having regular imaging tests of the breasts to look for signs of cancer. Different combinations of mammograms, ultrasound and MRI scans may be used.

Surgery

If you have a high risk of developing breast cancer, perhaps because you have one of the breast cancer genes, BRCA1 or 2, you may consider surgery to reduce your risk of breast cancer.

This may involve an operation to remove the breast tissue, called a prophylactic mastectomy. Another type of surgery that reduces the risk of breast cancer (although less than a mastectomy) is an operation to take away both ovaries. This is called a prophylactic oophorectomy. It may be considered by women who are also at increased risk of ovarian cancer.

Although these types of surgery greatly reduce the risk of cancer they don't take it away completely. Women who are considering this option need information and support when making up their mind about what to do.

Chemoprevention

Using drugs to stop a disease occurring is called chemoprevention. Some women have the option of taking part in a clinical trial to test whether a particular drug can reduce the risk of breast cancer developing. Hormone treatments, which are known to be effective in treating women with breast cancer, are being studied as risk reducing treatments. You can find trials in breast cancer chemoprevention in the trials section of our website.

What is DNA?

DNA is the material that genes are made from. Genes control the parts of our appearance that are inherited, like our hair and eye colour. They also control the renewal and repair of the tiny building blocks (cells) that our bodies are made up of.

The letters DNA stand for deoxyribose nucleic acid. DNA is made up of building blocks called nucleotides. Each nucleotide consists of: a phosphate, a sugar (which is deoxyribose) and a ‘base’. There are four different types of base in DNA nucleotides: thiamine, cytosine, adenine and guanine.

The structure of the DNA is a made up of two long strands. Each strand is a bit like a very long comb. The back bone, or spine, of each comb is made up by the phosphates and sugars and the different bases stick out from this spine, like the teeth sticking out on a comb. The bases of the two strands link up with one another, so that the spine of the strands, or combs, is on the outside, with the bases, or teeth, of the comb joined together inside.

The two strands are then coiled round one another, in a pattern a bit like a spiral staircase, called a double helix.

The DNA is very tightly coiled within the nucleus of our cells. Although it is invisible to the naked eye and can only be seen under high powered microscopes, the DNA from a single human cell, if it was uncoiled, would be about 1m (just over 3 feet) long.

The way in which the four different bases, thiamine, cytosine, adenine and guanine, are arranged along the DNA strands makes the blueprint for producing amino acids. These amino acids are the building blocks that make up the different proteins the cell needs.

So the pattern of the four bases on the strands of DNA is different in each and every one of us, and this unique pattern, in the nucleic acid in the nuclei of our cells, makes each of us who and what we are.

I have read that faulty genes can lead to cancer developing. How does this happen?

All of us begin life as a single cell. This cell goes on to divide countless times to produce the trillions of cells that make up an adult human being. Even after we reach adulthood, and stop growing, many of the cells in our body continue to multiply in order to produce new cells to replace old cells that are worn out, and die off.

This process of cell division, and multiplication, is very carefully controlled so that exactly the right number of cells are being produced at any one time. We do not fully understand how these controls work but at the level of individual cells the process of division is triggered by growth factors. These growth factors then switch on the genes within the cell genes so that the process of reproducing the cell begins.

Two types of gene are involved in the control of cell reproduction:

proliferation genes: these are genes which carry the information to make the proteins that stimulate the cell to divide
anti-proliferation genes: these are genes which carry the information to make proteins which put a brake on the process of cell division.

Normally there is a balance between these two sets of genes so that the cell only divides when it is supposed to.

We now know that in a number of human cancers there is a change, or mutation, of certain genes, that leads the cells to multiply in an uncontrolled way, forming the cancer.

These mutations may affect proliferation genes, causing them to become overactive, so making the cell divide excessively. Or they may affect anti proliferation genes, making them ineffective so that, once again, cell growth goes out of control.

Proliferation genes which if they become damaged, or mutant, can cause cancer are called proto-oncogenes. Once they become mutant they are called oncogenes. Anti-proliferation genes which can lead to cancer if they are damaged are called tumour suppressor genes.

In our cells the chromosomes, which carry the genes, are in pairs, which means we have two copies of every gene. Only one copy of a proto oncogene needs to mutate to an oncogene in order to start uncontrolled cell division. For tumour suppressor genes, both copies of the gene must be damaged before they become, and allow uncontrolled cell growth.

As time goes on more and more proto-oncogenes and tumour suppressor genes are being discovered and this offers the hope that we may be able to do more to treat, and even prevent, cancer in the future by being able to reverse the effects of mutations to these genes.

What causes breast cancer?

Unlike the link between smoking and lung cancer there is no obvious cause for breast cancer so the reason why the majority of these tumours develop is not known.

Having said this there are a number of things which are 'risk factors', which increase the chances of getting breast cancer (although most women who have one or more of these risk factors will still never actually get the disease). The two main groups of 'risk factors' are hormonal and genetic.

The hormonal influences on breast cancer development relate to the balance of female hormones in the body at different times of life. Things which have been shown to increase the chance of getting breast cancer are:

starting periods early, especially before the age of 11
entering the menopause late, above the age of 55
not having children, or having your first child over the age of 30
long term use of HRT (hormone replacement therapy) after the menopause.

On the other hand there are some hormonal influences which actually reduce the risk of breast cancer. These include:

starting periods later, over the age of 14
having an early menopause
having children, especially if your first pregnancy is before the age of 20
breast feeding.

Genetic risk factors relate to the discovery of two genes, called BRCA1 and BRCA2 which are abnormal in about 1 in 20 women with breast cancer. Women who inherit these abnormal, or mutated, BRCA1 or BRCA2 genes have an increased risk of developing breast cancer some time during their life - it is estimated that probably as many as 8 out of 10 women with one of the abnormal genes will get breast cancer if they live to the age of 80 (although some recent figures suggest the risk may actually be less than this, perhaps as low as 5 out of 10). Abnormalities of the BRCA1 gene are commoner than those of the BRCA2 and affect about 1 in 800 women.

The influence of things like diet and environmental factors is less certain although there is some evidence that obesity, a high fat diet and high alcohol consumption may all be slight risk factors.

One other influence is age, the longer a woman lives the more likely it is that a breast cancer will develop. So whilst overall about 1 in 12 women in the UK develop breast cancer this figure rises to 1 in 9 for women who have reached the age of 90.

Why do some women get breast cancer and others don't?

No-one really knows the answer to this question.

We do know some things that will increase a woman's chances of developing a breast cancer. For example, inheriting certain faulty genes or starting periods at a younger age than normal and entering the menopause later than normal all increase the risk of breast cancer developing.

But even if a woman has several of these 'risk factors' it still does not mean that she will get a breast cancer, whereas many women who have none of the known 'risk factors' still get the disease.

Until we know more about exactly how breast cancers develop and have a more precise understanding of the chemical and genetic changes that turn normal breast cells cancerous then the answer to this question will remain a mystery.

Is it true that if you have had relatives who have had a bowel cancer you may be at greater risk of getting a cancer yourself, and if so how big is the risk?

There are several medical conditions which run in families and which are known to increase the risk of getting a bowel cancer (a carcinoma of either the colon or the rectum). These include familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC).

It is also true that some families that do not have either of these conditions still seem to have a higher risk of bowel cancers, with more family members affected than would normally be expected.

Figures have now been worked out to show how great the risk is of getting a bowel cancer if you have had relatives who have had the disease.

For the normal population, 1 in 35 people will develop a bowel cancer at some time during their life. If one first degree relative has had a bowel cancer diagnosed when they were over the age of 45 then the risk increases to 1 in 17 people. (A first degree relative is a mother, father, sister, brother, daughter or son). If the first degree relative was below the age of 45 when their bowel cancer was found then the figure rises to 1 in 10. If two first degree relatives have had a bowel cancer, whatever their ages, then the risk is 1 in 6 and if three first degree relatives have been affected then 1 in every 2 people will be likely to get a cancer of either their colon or rectum.

As a guide, if these figures suggest your own risk might be 1 in 10 or greater then you should certainly see your family doctor and discuss whether or not you should go to a family cancer clinic or a bowel specialist for further tests and advice about your personal chances of getting a bowel cancer.

Cancer genetics - how cancer sometimes runs in families