Types of cancer of unknown primary (CUP)
Your doctor may want to take a sample of tissue (biopsy) from the secondary cancer. This is to examine the cells under a microscope.
By looking at their appearance and from doing tests on the cells themselves, doctors can usually be fairly confident about where they’ve spread from. For example, cells from a primary breast cancer that have spread to the liver will usually still look like breast cancer cells.
With CUP, doctors can’t tell what part of the body the cancer started in, but they may be able to find out the type of cell that has changed. This can give them more information about the possible behaviour of the cancer and will help them plan your treatment.
There are five different types of CUP. These are:
poorly differentiated carcinomas
squamous cell cancers
These develop from gland cells that line or cover certain organs in the body. The majority of people with CUP have an adenocarcinoma. The most common parts of the body for them to start in are the lungs, pancreas, bowel, kidneys, liver, stomach, ovaries, womb and breasts.
Poorly differentiated carcinomas
About 30% of people with CUP (3 in 10) have poorly differentiated carcinomas. Poorly differentiated means the cancer cells look very different from normal cells so it’s difficult to tell what type of cancer the primary was.
Squamous cell cancers
These develop from flat cells usually found on the surface of the skin or in the lining of internal surfaces of the body, such as the airways. About 5% of people with CUP (1 in 20) have squamous cell cancers. These can start in the lung, skin, head and neck area, gullet (oesophagus) and cervix.
About 3% of people with CUP (3 in 100) have neuroendocrine cancers. These are a type of cancer made up of specialised nerve cells that produce hormones.
The cells look extremely different to normal cells and it’s not possible to determine what type of cancer it is. About 5% of people with CUP (1 in 20) have this type. Further tests may sometimes be able to tell the doctors more about what type of cancer the primary was.