Types of CUP

Your doctor may want to take a sample of tissue or cells (biopsy) from the secondary cancer.

Usually, by examining the cells and doing tests on them, doctors can be fairly sure about where the cells have 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 which part of the body the cancer cells are from. Cancers are usually grouped according to their primary site. But they can also be grouped more broadly according to the type of cells they are made up of. Knowing the type of cell can give the doctors a better idea about where the cancer may have started and the best treatment to use.

CUP can be made up of five different types of cell, including:

  • adenocarcinomas
  • squamous cell carcinomas
  • neuroendocrine carcinomas
  • poorly differentiated carcinomas
  • undifferentiated cancers.


These develop from gland cells that line or cover certain organs in the body. Most people with CUP have an adenocarcinoma. The most common parts of the body that adenocarcinomas start are the breasts, lungs, bowel, pancreas, kidneys, liver, stomach, ovaries and womb.

Squamous cell carcinomas

These develop from flat cells usually found on the surface of the skin or in the lining of organs such as the lungs, gullet (oesophagus), cervix and the head and neck area.

Neuroendocrine carcinomas

These are a rarer type of cancer made up of specialised nerve cells that produce hormones.

Poorly differentiated carcinomas

Carcinomas start in the cells that line the body’s organs. Poorly differentiated means the cells look very different from normal cells, which makes it difficult to tell the type of primary cancer.

Undifferentiated cancers

Undifferentiated cancer cells look extremely different to normal cells. As they don’t look like either a carcinoma or a specific type of cancer, there is nothing to suggest which type of primary cancer it might be. Further tests may sometimes tell the doctors more about which type of cancer the primary might be.

Back to Understanding

What is cancer?

Cancer is a disease of our cells. Sometimes cells become abnormal and keep dividing to make more abnormal cells.