What should I do?
If you think you have this condition you should see a doctor within 48 hours.
How is it diagnosed?
Your doctor may suspect mouth cancer from symptoms such as mouth ulcers that do not heal. To confirm a diagnosis, the doctor will need to take a small sample of the affected tissue for analysis under a microscope (biopsy). A specialist may also request a scan of the body to check if other parts of the body have been affected.
What is the treatment?
The treatment of mouth cancer depends on how advanced the cancer is. It can be treated with surgery in combination with chemotherapy and/or radiotherapy.
Mouth cancer, also known as oral cancer, is where an abnormal group of cells (tumour) develops on the surface of the tongue, mouth, lips or gums.
Less commonly, it can occur in the salivary glands, tonsils and the part of the throat that leads from your mouth to your windpipe (the pharynx).
Symptoms of mouth cancer include:
- one or more mouth ulcers that do not heal
- red, or red and white, patches on the lining of your mouth or tongue
- a swelling in your mouth that lasts for more than three weeks
Types of mouth cancer
Healthcare professionals categorise cancers by the type of cells the cancer first develops in.
Squamous cell carcinoma is the most common type of mouth cancer, accounting for 9 out of 10 cases. Squamous cells are found in many places around the body, including the inside of the mouth and under the skin.
Squamous cell carcinomas are also a common cause of skin cancers.
Less common types of mouth cancer include:
- oral malignant melanoma - where the cancer starts in cells called melanocytes, which help give skin its colour
- adenocarcinomas - cancers that develop inside the salivary glands
What causes mouth cancer?
Mouth cancer occurs when something goes wrong with the normal cell lifecycle, causing them to grow and reproduce uncontrollably.
Risk for developing mouth cancer include:
- drinking alcohol (smokers who are also heavy drinkers have a much higher risk compared to the population at large)
- infection with the human papilloma virus (HPV), which is the virus that causes genital warts
- a diet that contains lots of red meat and fried food
Read more about the causes of mouth cancer.
Who is affected by mouth cancer?
Mouth cancer is an uncommon type of cancer, accounting for 1 in 50 of all cancer cases.
In the UK, just over 6,200 new cases of mouth cancer were diagnosed in 2009 (the latest year from which reliable data is available).
Most cases of mouth cancer first develop in older adults who are around 60 years of age.
Mouth cancer can occur in younger adults, but it's thought that HPV infection may be responsible for the majority of cases that occur in younger people.
Mouth cancer is more common in men than in women. This is thought to be due to the fact that, on average, men drink more alcohol than women.
Treating mouth cancer
There are three main treatment options for mouth cancer. They are:
- surgery - where the cancerous cells are surgically removed and, in some cases, some of the surrounding tissue
- chemotherapy - where powerful medications are used to kill cancerous cells
- radiotherapy - where high energy X-rays are used to kill cancerous cells
These treatments are often used in combination. For example, a course of radiotherapy and chemotherapy may be given after surgery to help prevent the cancer returning.
Read more about treating mouth cancer.
Complications of mouth cancer
Both surgery and radiotherapy can make speaking and swallowing difficult (dysphagia).
Dysphagia can be a potentially serious problem. If small pieces of food enter your airways and become lodged in your lungs, it could trigger a chest infection, known as aspiration pneumonia.
Read more about the complications of mouth cancer.
Reducing the risk
The three most effective ways to prevent developing mouth cancer (or prevent it re-ocurring after successful treatment) are:
- not smoking
- keeping to the recommended weekly limits for alcohol consumption (21 units for men and 14 units for women
- eating a 'Mediterranean-style diet', with plenty of fresh vegetables (particularly tomatoes), citrus fruits, olive oil and fish
It's also important that you have regular dental check-ups because dentists can often spot the early stages of mouth cancer.
If mouth cancer is diagnosed early, a complete cure is often possible using a combination of radiotherapy, chemotherapy and surgery.
An estimated 4 out of 5 people with early-stage mouth cancer will live at least five years after their diagnosis and many peole live much longer.
The outlook is poor if mouth cancer is diagnosed at a later stage, after the cancer has spread from the mouth into surrounding tissue. In these circumstances, just 1 in 5 people will live for at least five years after being diagnosed.
If you have any of the possible symptoms of mouth cancer, your doctor will carry out a physical examination and ask about your symptoms.
If mouth cancer is suspected, you will be referred to a specialist for further testing. This is usually an oncologist (a doctor who specialises in the treatment of cancer) or an ear, nose and throat (ENT) specialist.
It may be necessary to remove a small sample of affected tissue to check for the presence of cancerous cells. This procedure is known as a biopsy.
There are three main methods used to carry out a biopsy in cases of suspected mouth cancer. They are outlined below.
A punch biopsy may be used if the suspected affected area of tissue is in an easily accessible place, such as your tongue or the inside of your mouth.
The area is first injected with a local anaesthetic to numb it. The doctor will then cut away a small section of affected tissue and remove it with tweezers.
The procedure is not painful, but can feel a little uncomfortable.
Fine needle aspiration (FNA)
A fine needle aspiration (FNA) is a type of biopsy used if it is suspected a swelling in your neck is the result of mouth cancer.
During a FNA, the doctor will insert a sharp needle into the lump and draw out a small sample of tissue and fluids. The sample is then checked for cancerous cells.
Local anaesthetic is used to numb your neck, so an FNA is not painful. However, it can be uncomfortable and you may have bruising after the procedure.
A panendoscopy is a procedure used to obtain a biopsy when the suspected tissue is at the back of your throat or inside one of your nasal cavities.
The doctor uses an instrument called a panendoscope. This is a long thin tube that contains a camera and light source. The panendoscope is guided through your nose, then used to remove a small section of tissue for the biopsy.
The panendoscope can also check whether cancer has spread from your mouth to further down your throat, such as your larynx (voice box), oesophagus (gullet) or trachea (windpipe).
If the biopsy shows the presence of cancer, further testing will be required to check how advanced it is and how far it has spread. This is known as the stage of the cancer.
Cancer spreads from the site of the initial tumour into the lymphatic system. The lymphatic system is a series of vessels and glands (or nodes) spread throughout your body, much like your blood circulation system. These glands produce many of the specialised cells needed by your immune system.
Once the cancer reaches the lymphatic system, it is capable of spreading to any other part of your body, including your bones, blood and organs. It is uncommon for mouth cancer to spread further than the surrounding lymph nodes, although in some cases it may also spread to surrounding bones, such as the jaw bone, and in some cases your lungs.
Therefore, the tests will examine your lymph nodes, bones and the tissue near the site of your initial tumour to check for the presence of other tumours.
The tests that may be used include:
- an X-ray
- a magnetic resonance imaging (MRI) scan
- a computerised tomography (CT) scan
- a positron emission tomography (PET) scan
A PET scan involves injecting a part of your body with a radioactive ‘tracer’ chemical that can be seen on a special camera.
Further biopsies on nearby lymph nodes may also be carried out.
Staging and grading
Once these tests have been completed it should be possible to tell what stage and grade your cancer is:
- staging is a measure of how far the cancer has spread
- the grade is an assessment of how aggressive the cancer is and how fast it is likely to spread in future
This will help determine whether you have:
- early mouth cancer (usually curable)
- intermediate mouth cancer (may be curable)
- or advanced mouth cancer (not usually curable, but it is usually possible to slow the spread of the cancer and extend lifespan)
There are three grades of mouth cancer:
- low-grade – where the cancer spreads slowly
- moderate-grade – where the cancer spreads at a medium pace
- high-grade – where the cancer is very aggressive and likely to spread quickly if untreated
The grading of your cancer can often determine whether you require immediate treatment or whether treatment can be safely delayed for a period of time – read more about treating mouth cancer.
If you are diagnosed with mouth cancer you may need to be referred to a larger specialist cancer centre or clinic as it is an uncommon form of cancer. This may requiure you to travel to a nearby city.
Your care team
These centres and clinics use multidisciplinary teams (MDTs) for the treatment of mouth cancer. An MDT is made up of a number of specialists, including:
- a surgeon
- a clinical oncologist (specialist in the non-surgical treatment of cancer, such as radiotherapy and chemotherapy)
- a pathologist (specialist in diseased tissue)
- a radiologist (specialist in radiotherapy)
- a dentist
- a dietitian
- a social worker
- a psychologist
- a speech and language therapist
You may also be assigned a clinical nurse specialist (CNS) who specialises in the treatment of mouth cancer. The CNS will be your first point of contact and will provide information about your treatment plan and the various support services available.
Your treatment plan
Your recommended treatment plan will depend on how far the cancer has spread.
If the cancer has not spread beyond the mouth or oropharynx (the area of the throat at the back of your mouth), it may be possible to completely cure the cancer using a combination of surgery, radiotherapy and chemotherapy.
If the cancer has spread to other parts of the body, then achieving a cure is unlikely. However, it is possible to slow the progress of the cancer and help relieve symptoms by using surgery, radiotherapy and chemotherapy.
Deciding what treatment is best for you can be difficult. Your care team will make recommendations, but the final decision will be yours.
Before going to hospital to discuss your treatment options, you may find it useful to write a list of questions to ask the specialist. For example, what are the advantages and disadvantages of particular treatments.
Before treatment begins
Before treatment for mouth cancer begins, you will be given a full dental examination and any necessary dental work will need to be carried out. The radiotherapy will make your teeth more sensitive and vulnerable to infection, so it is important to have a good level of dental hygiene before treatment begins.
If you are smoking and drinking alcohol, it is recommended that you stop, because quitting will increase the chances of your treatment being successful.
Your CNS and your doctor can provide help and support if you are finding it difficult to quit smoking and drinking.
Read more about quitting smoking
For mouth cancer, the aim of surgical treatment is to remove any affected tissue while minimising damage to the rest of the mouth.
Photodynamic therapy (PDT)
If the cancer is in its early stages, it may be possible to remove any tumours using a type of laser surgery known as photodynamic therapy (PDT). PDT involves taking a medicine that makes your tissue sensitive to the effects of light. A laser is then used to remove the tumour.
Other forms of surgery
If your cancer is more advanced, it may be necessary to remove part of your mouth lining and, in some cases, facial skin. The removed skin can be replaced using a skin flap. This is a piece of skin taken from your forearm or chest, which is then grafted to the affected area.
If your tongue is affected, part of the tongue will have to be removed. This is known as a partial glossectomy. The tongue is then reconstructed using grafted tissue.
If the cancer has spread to your jawbone it will need to be surgically removed. The jawbone can be replaced by taking bone from another part of your body and grafting it in place.
Occasionally, other bones, such as cheekbones, may have to be removed to completely remove the cancer. These bones can be replaced with prosthetics, which are moulded pieces of plastic designed to replicate the shape and appearance of any removed bones. Modern prosthetics are usually very realistic. Although they will take time to get used to, your physical appearance should be largely unaffected.
During surgery, your surgeon may remove lymph nodes near the site of the initial tumour. This is known as a neck dissection. Neck dissections are often carried out as a preventative measure, as the nodes may contain small amounts of cancerous cells that cannot be detected through testing.
Radiotherapy uses doses of radiation to kill cancerous cells. It may be possible to remove the cancer using radiotherapy alone, but it is usually used after surgery to prevent the cancer from reocurring.
The treatment is normally given every day over the course of three to seven weeks, depending on the size of the cancer and how far it has spread.
While it kills cancerous cells, radiotherapy can also affect healthy tissue, and it has a number of side effects, including:
- sore, red skin (like sunburn)
- mouth ulcers
- sore mouth and throat
- dry mouth
- loss of, or changes in, taste
- loss of appetite
- feeling sick
- stiff jaw
- bad breath
Any side effects will be monitored by your care team and treated where possible.
The side effects of radiotherapy can be distressing, but most of them will pass once the radiotherapy is complete.
Internal radiotherapy is a type of radiotherapy often used to treat cancers of the tongue that are in their early stages. It involves sticking radioactive wires or needles directly into the tumour while you are under a general anaesthetic (put to sleep). The wires or needles then release a dose of radiation into the tumour.
While the internal radiotherapy is taking place, you will be kept in a single room at the hospital. While the levels of radiation you are receiving are generally safe, your treatment staff will only be able to spend short periods of time in the room with you. This is because they are dealing with radiation every day, so it is necessary to minimise any exposure as a precaution.
Visits by friends and family will also have to be restricted due to the risk of exposure. Pregnant women and children will not be able to visit you.
Most courses of internal radiotherapy last one to eight days.
The radioactive implants will cause your mouth to become swollen, and you will experience some pain five to 10 days after the implants are removed. However, the pain should subside within a few weeks. During this time, you may find it more comfortable to eat cool, plain, soft foods, and avoid drinking spirits or smoking.
Chemotherapy is often used in combination with radiotherapy when the cancer is widespread, or if it is thought there is a significant risk of the cancer returning.
Chemotherapy involves the use of powerful cancer-killing medicines. These medicines damage the DNA of the cancerous cells, interrupting their ability to reproduce.
Medicines used in chemotherapy can sometimes damage healthy tissue as well as the cancerous tissue. Adverse side effects are common and include:
- sore mouth
- mouth ulcers
- feeling sick
- being sick
- hair loss
The side effects should stop once the treatment has finished.
Chemotherapy can also weaken your immune system and make you more vulnerable to infection.
Cetuximab is a new type of medication used to treat advanced cases of mouth cancer. It is usually used in combination with radiotherapy or chemotherapy.
Cetuximab is a monoclonal antibody. Monoclonal antibodies are designed to directly target and attack cancer cells. This is why monoclonal antibody therapy is sometimes referred to as targeted therapy.
Cetuximab targets special proteins found on the surface of cancer cells, known as epidermal growth factor receptors. These receptors help the cancer to grow, so by targeting these proteins, cetuximab prevents the cancer from spreading. Cetuximab is given through a drip into your vein, which slowly administers the first dose over the space of a few hours. After this, further doses are given on a weekly basis and should only take an hour.
The side effects of cetuximab are usually mild. They include:
Cetuximab has been known to trigger allergic reactions in some people, such as a swollen tongue or throat. Occasionally, an allergic reaction can be severe and life-threatening. This is known as an infusion reaction. Infusion reactions occur in around 1 in 30 people receiving cetuximab.
Most infusion reactions happen within 24 hours of the first time somebody begins treatment, so you will be closely monitored once your treatment begins. If you begin to have symptoms of an infusion reaction, anti-allergy medicines can be used to relieve them.
Owing to these precautionary measures, death from an infusion reaction in people taking cetuximab is very rare. It occurs in less than one in 1,000 cases.
Symptoms of oral cancer include:
- red, or red and white, patches on the lining of your mouth or tongue
- one or more mouth ulcers that do not heal after three weeks
- a swelling in your mouth that lasts for more than three weeks
- pain when swallowing (dysphagia)
- a tooth, or teeth, that becomes loose for no obvious reason
- a persistent pain in the neck
- a hoarse voice
- unexplained weight loss
- unusual changes in your sense of taste
- the lymph nodes (glands) in your neck become swollen
When to seek medical advice
Many of the symptoms listed above can also be caused by less serious conditions, such as minor infections, that do not usually require a medical diagnosis.
It is strongly recommended that you visit your doctor if you develop any of the symptoms listed above and they last for more than three weeks. Symptoms of an infection usually clear up much sooner than this. It is especially important to seek medical advice if you are a heavy drinker or smoker.
Living with cancer
Having mouth cancer doesn't necessarily mean you'll have to give up work. But you may need quite a lot of time off, and you may not be able to carry on completely as before during your treatment.
If you have cancer you're covered by the Disability Discrimination Act. This means that your employer is not allowed to discriminate against you because of your illness. They have a duty to make ‘reasonable adjustments’ to help you cope. Examples of these include:
- allowing you time off for treatment and medical appointments
- allowing flexibility with working hours, the tasks you have to perform or your working environment
The definition of what is ‘reasonable’ depends on the situation. For example, how much it would affect your employer’s business.
It will help if you give your employer as much information as possible about how much time you will need off and when. Talk to your human resources department if you have one. Your union or staff association representative should also be able to give you advice.
If you're having difficulties with your employer, you may be able to receive help from your union or your local Citizens Advice Bureau.
Relationships with others
It is not always easy to talk about cancer, either for you or your family and friends. You may sense that some people feel awkward around you or avoid you. Being open about how you feel and what your family and friends can do to help may put them at ease. Do not feel shy about telling them that you need some time to yourself, if that is what you need.
Money and financial support
If you have to stop work or go part-time because of your cancer, you may find it hard to cope financially. If you have cancer or you are caring for someone with cancer, you may be entitled to one of the following areas of financial support:
- If you have a job, but cannot work because of your illness, you are entitled to Statutory Sick Pay from your employer.
- If you don't have a job and cannot work because of your illness, you may be entitled to Employment and Support Allowance.
- If you are caring for someone with cancer, you may be entitled to Carer’s Allowance.
- You may be eligible for other benefits if you have children living at home or if you have a low household income.
Find out as early as possible what help is available to you. Speak to the social worker at your hospital who can give you the information you need.
People being treated for cancer are entitled to apply for an exemption certificate, giving them free prescriptions for all medication, including medicine for unrelated conditions.
The certificate is valid for five years and you can apply for it through your doctor or cancer specialist.
Want to know more?
- Carers Direct: benefits for carers and benefits for the person you care for
- GOV.UK: benefits and financial support
- Citizens Advice Bureau
- News: Q&A: free prescriptions
- Money Advice Service
Talk to others
If you have questions, your doctor or nurse may be able to reassure you. You may find it helpful to talk to a trained counsellor or psychologist, or to someone at a specialist helpline. Your doctor surgery will have information on these. Some people find it helpful to talk to other people who have mouth cancer, either at a local support group or in an internet chatroom.
Caring for others with mouth cancer
Being a carer is not an easy role. When you are busy responding to the needs of others it can deplete your reserves of emotional and physical energy and make it easy for you to neglect your own health and mental wellbeing. Research on carers’ health shows that high numbers of carers suffer health effects through caring. If you are trying to combine caring with a paid job or looking after a family, this can cause even more stress.
If you are caring for someone else, it is important to look after yourself and get as much help as possible. It is in your best interests and those of the person you are caring for.
Look after your health
Eat regularly and healthily. If you do not have time to sit down for every meal, try to make time to sit down for at least one of your day's meals. Instead of relying on fast food snacks, go for healthier options, such as fruit.
Look after your emotional health
As well as exhaustion, isolation and worries about the person you are caring for, it is understandable if there are times when you feel resentful and then guilty for feeling like this. These feelings are natural.
Look for support
Friends and family may not always understand what you are going through and it can be helpful to talk to people in the same situation. Carers Direct has a lot of useful information on its website and runs a helpline on 0808 802 0202.
Dysphagia is the medical term for difficulty swallowing. It is easy to take your ability to swallow food and liquid for granted, but in reality the process relies on a complex interaction of muscles, which can be easily disrupted.
Surgery and radiotherapy can affect your tongue, mouth or throat, resulting in dysphagia. Dysphagia is a potentially serious problem because, aside from the risk of malnutrition, there is a chance that small particles of food could enter your airways and become lodged in your lungs. This can trigger a chest infection, known as aspiration pneumonia.
If you are having problems swallowing, a speech and language therapist (SLT) will need to assess your swallowing reflex. One way an SLT can do this is to perform a test known as a videofluoroscopy, which involves adding a special dye to liquid and food that you swallow. The dye highlights your swallowing reflexes and by using X-rays your SLT can see if there is a risk of food entering your lungs.
If this is the case, it may be necessary in the short term to provide you with a feeding tube, which will be directly connected to your stomach. The SLT will teach you exercises so that you can 'relearn' how to swallow properly.
Your ability to swallow will improve as you learn the exercises and the damaged tissue is allowed to heal. However, there is a chance your swallowing reflex will never fully recover.
In some circumstances, you may have to alter your diet to make swallowing easier. A nutritionist can give you dietary advice.
Much like swallowing, your ability to speak clearly is governed by a complex interaction of muscles, bones and tissue, including your tongue, teeth, lips and soft palate (a section of tissue found at the back of the mouth).
Radiotherapy and surgery can affect this process and make it difficult to pronounce certain sounds. In severe cases, you may have problems making yourself understood.
An SLT will help you improve your verbal communication skills by teaching you a series of exercises that develop your range of vocal movements and teach you new ways of producing sounds.
The emotional impact of living with mouth cancer can be significant. Many people report experiencing a roller-coaster effect.
For example, you may feel down when you receive a diagnosis, but feel up when the cancer responds to treatment. Then you may feel down again as you try to come to terms with the side effects and after effects of your treatment.
This type of emotional disruption can sometimes trigger depression. Signs that you may be depressed include:
- feeling down or hopeless during the past month
- no longer taking pleasure in the things you enjoy
Contact your doctor for advice if you think you may be depressed. There are a range of effective treatments for depression, including antidepressant medication and talking therapies, such as cognitive behavioural therapy (CBT).
Read more about depression and [coping with cancer].
You may also find the Mouth Cancer Foundation website a useful resource. It's the UK’s leading charity for people affected by mouth cancer.
Cancer begins with a change in the structure of DNA. DNA provides our cells with a basic set of instructions, such as when to grow and reproduce.
A change in DNA structure is known as a mutation, and it can alter the instructions that control cell growth. This means that cells continue to grow instead of stopping when they should. This causes the cells to reproduce in an uncontrollable manner, producing a lump of tissue called a tumour.
How mouth cancer spreads
There are two ways mouth cancer can spread:
- directly – the cancer can spread out of the mouth and into nearby tissues, such as surrounding skin or into the back of the jaw
- via the lymphatic system – the lymphatic system is a series of glands (or nodes) located throughout your body (similar to the blood circulatory system), glands produce many specialised cells needed by your immune system to fight infection
Mouth cancer that spreads to another part of the body is known as metastatic oral cancer.
Exactly what triggers the changes in DNA that lead to mouth cancer and why only a small number of people develop mouth cancer is still uncertain.
However known risk factors include:
Smoking and alcohol
The two leading causes of mouth cancer are smoking cigarettes (or other tobacco products, such as pipes or cigars) and drinking too much alcohol. Both of these substances are carcinogenic, which means they contain chemicals that can damage the DNA in cells and lead to cancer.
The risk of mouth cancer increases significantly in somebody who is both a heavy smoker and heavy drinker.
For example, research has shown that if you smoke 40 cigarettes a day, but do not drink alcohol, you are five times more likely to develop mouth cancer than someone who does not drink or smoke.
If you do not smoke, but drink an average of 30 pints a week, your risk also increases by a factor of five.
However, if you smoke more than 40 cigarettes a day and you drink an average of 30 pints a week, you are 38 times more likely to develop mouth cancer.
Betel nuts are mildly addictive seeds taken from the betel palm tree, and are widely used in many southeast Asian ethnic communities, such as people of Indian and Sri Lankan origin.
They have a stimulant effect similar to coffee. Betel nuts also have a carcinogenic effect, which can increase the risk of mouth cancer. This risk is made worse as many people enjoy chewing betel nuts along with tobacco.
Due to the tradition of using betel nuts, rates of mouth cancer are much higher in ethnic Indian and Sri Lankan communities than in the population at large.
Smokeless tobacco is a general term used to refer to a range of products, such as:
- chewing tobacco
- snuff – powdered tobacco designed to be snorted
- snus – a type of smokeless tobacco popular in Sweden, which is placed under your upper lip, where it is gradually absorbed into your blood
Smokeless tobacco products are not harmless, as many people mistakenly assume, and many increase your risk of developing mouth cancer, as well as other cancers, such as liver cancer, pancreatic cancer and oesophageal cancer.
Smoking cannabis has also been linked to an increased risk of mouth cancer. Regular cannabis smokers may have a higher risk than tobacco smokers because cannabis smoke contains higher levels of tar than tobacco smoke, and tar is carcinogenic.
Human papilloma virus (HPV)
The human papilloma virus (HPV) is the name of a family of viruses that affect the skin and moist membranes that line your body, such as those in your cervix, anus, mouth and throat.
You can contract a HPV infection by having sexual contact with a person already infected – you do not have to have 'full sex'; just close skin-to-skin contact.
Infection with some types of HPV can cause abnormal tissue growth and other changes to the cells, which can lead to the development of cervical cancer.
There is evidence that some types of HPV infection could also cause abnormal tissue growth inside the mouth, triggering some cases of mouth cancer.
It is thought HPV infection is the probable cause of mouth cancer in young people who have few or none of the expected risk factors.
There is evidence that a diet high in red meat, processed food and fried food can increase your risk of developing mouth cancer.
Poor oral hygiene
There is evidence that poor oral hygiene, such as having tooth decay, gum disease, not brushing your teeth regularly and having ill-fitted dentures (false teeth) can increase your risk of mouth cancer.
Qat is a green-leafed plant found in Africa and southern Arabia. There is a long tradition in many countries of chewing qat as it has a mild stimulant effect.
There is some limited evidence that qat may increase the risk of mouth cancer, but because many people chew qat with tobacco, it is hard to estimate the independent risk factor of qat.