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Your GP will ask you questions about your symptoms, such as what they are like and how long you have had them.
Investigations will depend on the type of cancer the doctors think you may have.
S/he may examine you - for example to feel for any lumps or swellings - and will check your medical records to see what illnesses you have had in the past. S/he may ask you questions about your lifestyle (eg whether you smoke) and about the work you do.
If you don't know who your GP is or how to contact them, you find contact details of local GP's here.
If s/he thinks you may have cancer s/he will arrange some more tests, or send you to see a specialist doctor. There are NHS cancer referral guidelines to help GPs decide who may need to see a specialist, and how quickly.
There are many tests that can help doctors to find out what is wrong. Tests may include blood tests, x-rays and scans. For some cancers the doctor may need to look more closely at the inside of your body using a special telescopic instrument. For example a bronchoscope can be passed through the mouth and down into the lung, to look for signs of lung cancer.
The surest way to tell whether you have cancer is to take a sample of cells or tissue from the place the cancer might be, and look at it under a microscope. This is called a biopsy.
Then, if you do have cancer, it will need to be classified according to its grade and stage. Doctors work out the grade by looking at cancer cells under a microscope, and seeing how much they still look like normal cells. The less they look like normal cells, the higher the grade of the cancer. Higher grade cancers are more likely to grow and spread. The stage of the cancer means whether it has spread, and if so, how much. Doctors need the information about grade and stage to plan your treatment.
It may take a few days before your doctor has the results of all the tests. S/he will then be able to tell you whether you have cancer, and talk with you about your treatment options.
You can find out more about the tests you might have in our 'common tests' section.