Cancer of unknown primary (CUP)
CUP is not a single disease. There are more than 200 different types of primary cancer. Different types of cancer have different risks and causes. For example, the biggest cause of lung cancer in the UK is smoking. And we know that overexposure to ultraviolet light from the sun or sun beds increases your risk of skin cancer.
Cancer is a disease usually caused by many different factors coming together. Our risk of cancer depends on a combination of our genes, environment and lifestyle.
Read more about the causes of cancer
CUP is more common in older people. In the UK, almost 60 out of 100 people (almost 60%) diagnosed with CUP are 75 and over.
Smoking is the biggest preventable cause of cancer in the UK. This includes breathing in other people’s cigarette smoke.
There is some evidence that smoking also increases the risk of developing CUP.
Find out about smoking and support to help you stop
There is some evidence that suggests drinking alcohol may increase the risk of CUP. Cutting down on alcohol has lots of benefits, including reducing your cancer risk.
The NHS recommends both men and women drink no more than 14 units of alcohol a week.
Overweight and obesity is the second biggest preventable cause of cancer after smoking. Losing weight or avoiding putting on more weight can help reduce the risk of cancer.
There is some evidence that people who are overweight have an increased risk of developing CUP.
Find out about how obesity can cause cancer and top tips about being healthier
Stories about potential causes are often in the media. It isn’t always clear which of the ideas reported are supported by good evidence.
You might have heard about a possible cause which we haven’t included here. This is either because there is no evidence to support it, or because it is not fully clear what the evidence shows.
Read more about cancer myths and controversies
People diagnosed with cancer often feel strongly that they must find out what caused it. But for many types of cancer there is no obvious cause.
Cancer can just happen because of bad luck. Over years, a cell gathers changes to its genetic code that eventually make it become cancerous.
Cancer causing chemicals, such as those in cigarettes, may trigger one or two of the changes. But often, something just goes wrong in the DNA of the cell by itself – a bit like a spelling mistake in the genetic code. The damaged cell then begins to grow and divide much more quickly than normal cells. Or it doesn't die off as a normal cell would. The overgrowth of cells forms a tumour.
Find out more about how cancer starts
Being diagnosed with any type of cancer is difficult to accept. You may find yourself spending a lot of energy trying to work out what caused it.
Remember that often the cause of the cancer is never found. And if doctors do find the cause, this is unlikely to change your treatment or how well it works.
Everyone copes with this in their own way. You may find it helpful to focus your energy on getting through your treatment and staying as well as you can.
Last reviewed: 21 May 2024
Next review due: 21 May 2027
Cancer of unknown primary (CUP) means that cancer spread (secondary cancer) has been found in your body, but doctors don't know where the cancer started (the primary tumour).
Most people are diagnosed with CUP after they become unwell and go to A&E. Others start by seeing their GP. Find out what to expect when you see a GP and the tests you might have.
There is no staging system for cancer of unknown primary (CUP). Doctors can group CUP by the type of cell the cancer started in.
Treatment for CUP depends on a number of things, including where the cancer is and your general health. You might have a targeted cancer drug or chemotherapy. Sometimes you may have surgery or radiotherapy to help control your symptoms.
Survival for cancer of unknown primary depends on many different things such as the type and stage of cancer. No one can tell you exactly how long you will live.
Cancer of unknown primary (CUP) means that cancer spread has been found somewhere in your body (secondary cancer) but your doctors can't find where the cancer started (the primary cancer).
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