What is unknown primary cancer?
This page tells you what unknown primary cancer (UPC or CUP) is.
What is unknown primary cancer?
This means that you have a cancer, but your doctor is not sure where it started to grow.
What a primary cancer is
The place where the cancer starts growing is called the primary site. Cells from this primary site can break away and spread to other parts of the body. They can then form other cancers, which are known as secondary cancers or metastases.
Cancers are named and treated according to their primary site - even if they have spread to other parts of the body. For example if you have lung cancer that has spread to the liver, it is a lung cancer with liver metastases or secondaries. It is not called liver cancer. This is because the cells in the liver are actually cancerous lung cells. They are not liver cells that have become cancerous.
Why can't they find the primary cancer?
Sometimes secondary cancers are found but the doctor is unable to find the primary site. This is called cancer of unknown primary (UPC or CUP). The secondary cancer may have grown quickly, whilst the primary cancer is still very small. Or the primary cancer may have disappeared while the secondary cancers are thriving.
Examining the cells
A specialist will examine your cancer cells under a microscope. But sometimes cancer cells don’t look like any particular type of normal cell. So the doctor cannot tell where they came from.
You can view and print the quick guides for all the pages in the About UPC section.
Your body is made up of billions of cells that can only be seen under a microscope. The cells are grouped together 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, causing the cell to carry on dividing until it forms a lump or tumour. For more information about cells, how they multiply and what happens when it goes wrong, look in the cells and cancer section of CancerHelp UK.
A tumour can be either benign or malignant. A benign tumour does not spread to other parts of the body. But a malignant tumour is a cancer and can spread to other parts of the body.
The place where the cancer starts growing is called the primary site. If the cancer is not treated, cells from this primary site can break away and spread to other parts of the body. These escaped cells can then form other cancers, which are known as secondary cancers or metastases. There is more information about this in the how cancers grow section of CancerHelp UK.
Cancers are named and treated according to where they started developing in the body even if they have spread to other parts of the body. For example if you have lung cancer that has spread to the liver, it is a lung cancer with liver metastases or secondaries. It is not called liver cancer. This is because the cells in the liver are actually cancerous lung cells. They are not liver cells that have become cancerous.
Normally it is easy to find the primary cancer. Either it will be producing symptoms or it will be seen on a scan. But sometimes secondary cancers are found in one or more parts of the body, but the doctor is unable to find the primary site. This is called cancer of unknown primary (UPC or CUP).
There are a number of reasons why the primary cancer cannot be found. It may be that
- The secondary cancer has grown very quickly, whilst the primary cancer is still very small - very small primary cancers may not be seen on scans
- Your immune system has successfully attacked the original primary cancer and it has disappeared altogether, while the secondary cancers are thriving - this is not common, but it can happen
- The primary cancer may have been ‘sloughed off’. This can happen if it was in the digestive system - a small cancer becomes detached from the wall of the bowel, for instance, and is passed out of the body with the faeces.
The different types of cells in your body are named firstly according to the body organ they belong to, and secondly according to the job they do. When a cancer develops, it is named according to the type of cell it starts in.
So the type of cancer depends on what the cells look like under a microscope. The cells may look like breast cells that have become cancerous for instance. But sometimes cancer cells don’t look like any particular type of normal cell. The cells are too primitive. They have not become specialised enough to look like breast cells or lung cells. Cells like this are known as ‘poorly differentiated’. This can make it difficult for the doctor to tell what kind of cell the cancer started from. If this is the case, the cancer will be called a poorly differentiated cancer of unknown primary.
Most cancers are cancers of the epithelial cells. Epithelial cells are found in tissues throughout the body. Cancers that start in epithelial tissue are called carcinomas. More than 85% of all cancers are carcinomas. Other types of cancers develop from different types of body cell. They include
- Sarcomas, which develop from the cells muscles, fat, nerves or other soft tissues
- Leukaemias, which are cancers of white blood cells found in the bone marrow and
- Lymphomas, which are cancers of the cells of the immune system
There is more about different cell types and cancer in the about cancer section of CancerHelp UK.
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