Sometimes cancer spreads through the body, and doctors are not able to find where it first started.

What is cancer of unknown primary?

Cancer can begin anywhere in the body when cells grow abnormally into a lump or tumour. This is called the primary cancer. 

The primary cancer cells can spread through the body and grow in other places.

Cancer of unknown primary is cancer that has spread through the body and doctors are not able to find where it first started.

Cancer is a disease of the body's cells. It starts in our genes. Our bodies are constantly making new cells, a process controlled by certain genes. Cancers are caused by damage to these genes. As the damaged cells replicate a lump or tumour is formed. 

Tumours can be:

  • Benign - not cancerous. These do not spread to other parts of the body.
  • Malignant - cancerous


If this primary cancer spreads to other parts of your body, the cancer cells usually still look the same.  

For example, if cancer began in the breast and then spread to the lungs, the cancer cells in the lungs will still look like breast cancer cells. This would be called secondary cancer in the lung.

It is diagnosed as cancer of unknown primary when doctors are cannot tell what type of cancer cells they are. 

Why can’t the doctors find the primary cancer?

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

  • the primary cancer is very small
  • your immune system killed the primary cancer
  • the cancer is in many parts of your body and it’s not clear where it started first
  • the primary cancer was removed during surgery for another condition and the doctors did not know the cancer was there

Cancer of unknown primary symptoms

The symptoms you have may depend on where the cancer is in your body. 

Signs and symptoms of cancer may include:

  • a lump on any part of your body
  • pain that is in one part of your body and does not go away
  • a cough that does not go away
  • change in toilet habits
  • fever for no reason that does not go away
  • night sweats
  • weight loss for no reason

Having these symptoms does not mean you have cancer, but it is important to get any changes checked by your doctor.

Tips for talking to your doctor

  • make a list of what you are feeling and how often it happens, including as much detail as possible
  • think about your family/whānau history of cancer and tell your doctor
  • go back to your doctor if you don't feel better, even if tests show you don't have a problem - you can ask for a second opinion if you want one 
  • take a family/whānau member or friend with you to the appointment for support

Diagnosing cancer of unknown primary

The tests used to diagnose cancer of unknown primary will depend on what symptoms you have. 

Your doctor will discuss these symptoms with you and suggest several tests to check for cysts, tumours or other changes.

These tests may include:

Blood tests
A blood sample is taken.

A biopsy takes a small sample of the abnormal cells to check if they're cancerous.

Tumour marker tests
Tests on blood or tissue samples to learn more about the cells.  

Scans such as MRI, CT, or PET-CT create pictures of the inside of your body to learn more about the cancer and where it is in your body. 

A mammogram is an X-ray of your breast which uses a low dose of radiation.

An instrument called an endoscope is used to look inside the body and remove small tissue samples. 

After a diagnosis

If your test results show cancer, this can be a difficult time, and feelings can change from one moment to the next. 

Everyone reacts differently when they learn they have cancer. There is no right or wrong way to feel. 

Talk about your treatment options with your doctor, family and friends. Ask for as much information as you need. It is up to you how involved you want to be in decisions about your treatment. 

Staging cancer of unknown primary

Based on your test results, the treatment team will give the cancer a stage between 1 and 4.

This is based on:

  • the size of your cancer (T)
  • if there is cancer in your lymph nodes (N)
  • if the cancer has spread to other parts of your body (M)

In general, the higher the number the more it has spread in your body. The treatment team use this to plan the best treatment options for you. 

Prognosis for cancer of unknown primary

The prognosis is the likely outcome of a disease. 

If you hear you have advanced cancer, you may wonder how long you have left to live.

This can be a difficult question to ask. You could ask your treatment team to describe the best-case scenario, worst-case scenario and typical outcomes for your cancer.

The doctors will look at the type and stage of the cancer as well as your general health to give a prognosis, but no doctor can say what the exact outcome for you will be. 

It is also OK not to ask this question or to say that you don't want to know. It is always your choice, and your feelings about this may change.

Treatment of cancer of unknown primary

Because cancer of unknown primary has spread through your body, it is usually treated as advanced cancer. 

The treatment options include:

  • chemotherapy
  • radiation treatment
  • hormone treatment
  • surgery

The aim of treatment is to control any symptoms caused by the cancer and to maintain or improve your quality of life.

Palliative care

Palliative care aims to improve your quality of life. It is not just about end of life care. 

Palliative care will help:

  • you to enjoy the best quality of life you can for as long as possible
  • make sure that your physical, practical, emotional and spiritual needs are looked after as well as possible
  • manage symptoms of your cancer
  • manage side effects of treatment
  • help you to feel in control of your situation
  • make your time as positive as it can be for you and your family/whānau

Speak with your treatment team about palliative care options for you and your family/whānau.

Need someone to talk to?
8:30 am to 5:00 pm Monday to Friday
0800 226 237 Information nurse

We know that going through cancer is tough and can raise many questions. You are not alone.

We have nurses and counsellors to answer your questions and provide the support you need. Get in touch

Last updated: July 1, 2021