The place where a 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.

Usually, it is easy to find the primary cancer, as it will either cause symptoms or be seen on a scan. Sometimes secondary cancers are found in one or more parts of the body, but the primary site cannot be found. This is called cancer of unknown primary (CUP).

There are different reasons why a primary cancer can’t always be found:

  • It may be too small to be picked up on scans or be hidden beside a larger secondary cancer
  • It might have disappeared, even though it has spread to other parts of the body. This can sometimes happen if the body’s immune system has successfully gotten rid of it
  • It might have been passed out of the body. e.g. a small cancer in the wall of the bowel may become detached and leave the body in the stools.

Cancer of unknown primary (CUP) affects about 3-5% of people with cancer. People with CUP are usually over 60, and often have more than one secondary cancer.

Symptoms of cancer of unknown primary

Symptoms of CUP vary depending on where the secondary cancer(s) are. General symptoms can include:

  • Unexplained weight loss
  • Loss of appetite
  • Feeling extremely tired all the time
  • Looking pale, feeling tired and breathless due to a lack of red blood cells (anaemia)

If any of these symptoms apply to you or if you have any concerns about similar symptoms, see your doctor.

Treatment of cancer of unknown primary

Patients with CUP are treated by a team of different specialists, called a multidisciplinary team. This team works together to create a treatment plan to suit the individual needs of the patient. The main treatment for CUP is chemotherapy. Other treatments include:

  • Radiotherapy
  • Surgery
  • Hormonal therapies are occasionally used to treat CUP if you have cancer with hormone receptors. They work by reducing certain hormones or preventing them from stimulating cancer cells to grow. They are commonly used to treat breast and prostate cancer and can also be used to treat cancer of the womb, ovaries or kidneys
  • Biotherapy is the use of newer and more targeted therapies to assist the body in fighting the disease
  • Supportive or palliative care with medicines to control your symptoms is an important part of treatment for people with CUP. If the cancer is very advanced, palliative care on its own may be recommended.