Cancer of unknown primary (CUP) means that cancer spread (secondary cancer) has been found in your body, but doctors don't knowwhere the cancer started (the primary cancer).
Your body is made up of billions of cells that can only be seen under a microscope. The cells grouptogether to make up the tissues and organs of our bodies.
Normally, cells only divide to replace old and worn out cells. Cancer develops when something inside a single cell goes wrong, making the cell carry on dividing until it forms a lump or atumour.
A tumour can be either non cancerous (benign) or cancerous (malignant). A benign tumour does not spread to other parts of the body. But a malignanttumour (cancer)canspread.
- Read more about how cancer starts
What is a primary cancer?
The primary cancer is the place where a cancer starts growing. Cells from this primary site maybreak away and spread to other parts of the body through the bloodstream or lymphatic system. These escaped cells can then grow and form other tumours, which are known as secondary cancers or metastases.
Doctors name and treat cancers according to where they first started developing, even if they have spread to other parts of the body.
For example,if you have bowelcancer that has spread to the liver, it is called bowelcancer with liver metastases or secondaries. It is not called liver cancer. This is because the cancerous cells in the liver are cancerous bowelcells. They are not liver cells that have become cancerous. Doctors confirm this by looking at the cells under the microscope.
- Read more about how cancers grow and spread
Looking for the primary cancer
It's normally straightforwardto find theprimary cancer. Usually, people go to their GP because of symptoms.The GP might then refer you to a specialist doctor andfortests that confirm where the cancer started (the primary tumour).
Sometimes secondary cancers are found in one or more parts of the body, but despite several tests, doctorscan't find the primary tumour.If tests show that you have a cancer that has spread, but your doctors can’t find the primary tumour, it’s called a malignancy of unknown primary origin (MUO).
You then have some initial tests to try to find out the primary cancer. If the primary cancer doesn’t show up on the initial tests, your doctor may refer you to a team of doctors who specialise in cancer of unknown primary (CUP).
The CUP specialist teammay arrange for more tests to search for the primary cancer. You have a confirmed cancer of unknown primary (cCUP) if they can't find the primary cancer after the specialised tests.
Why a primary cancer might not be found
There are differentreasons why doctors can't find a primary cancer. They don’t always know for certain why and how this happens. This might be because:
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the secondary cancer has grown very quickly, while the primary cancer is still very small – very smallcancers might not cause symptoms or be seen on scans
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your immune system has successfully attacked the original primary cancer and it has disappeared, while the secondary cancer is still growing (this is not common, but it can happen)
The most common places for secondary cancers to be found are the lungs, liver, bones, lymph nodes, and skin.
- Find out about lymph nodes and where they are in your body
How doctors know you have CUP
Doctors can oftentell the type of cancer by what the cells look like under a microscope. For instance, cells taken from atumour in the lung might look like breast cancer cells. So the doctor knows it is breast cancer that has spread to the lung, rather than a cancer that started in the lung.
Sometimes cancer cells don’t look like any particular type of normal cell. The cells are very abnormal andhave not become specialised enough to look like breast cells or lung cells, for example. Cells like this are known as poorly differentiated or undifferentiated.
This can make it very difficult for the doctor to tell what kind of cell the cancer started from.
Types of cells and cancer
Most cancers are cancers of theepithelial cells. Epithelial cells are found in the skin or tissues that line or cover the internal organs. Cancers that start in epithelial tissue are called carcinomas. Most cancers of unknown primary are types of carcinoma.
Other types of cancerdevelop from different types of body cell. They include:
- sarcomas, which develop fromcells of the connective and supportive tissue, such as bones,muscle, fat, blood vessels orother soft tissues
- leukaemias, which are cancers of white blood cells found in the bone marrow
- lymphomas, which are cancers that begin incells of theimmune system
- Read more about different cell types and cancer
How common is cancer of unknown primary (CUP)?
Around 8,600people arediagnosed with cancer of unknown primaryin the UK each year. That's about 2 out of every 100 cancers diagnosed (2%).
Who gets it?
Cancer of unknown primary can develop at any age. But almost 60 out of 100 cases(almost 60%) are in people over the age of 75.
- More information about the risks and causes of cancer of unknown primary
Symptoms of CUP
Symptoms of CUP depend on where the cancer has spread to in your body. Possible symptoms of CUP include:
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weight loss
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sickness and loss of appetite
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weakness or feeling very tired
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pain
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breathlessness
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a cough that won't go away
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swollen lymph nodes
These symptoms listed here are more often caused by other medical conditions. But if you have any of them it is important to see your doctor.
- Read more about the signs and symptoms of cancer
