Cancer of unknown primary (CUP)

Understanding your diagnosis

Cancer of unknown primary (CUP)

Understanding your diagnosis

Your specialist gets a lot of information about your cancer from your test results.

Your specialist uses this information to explain how the cancer could affect you in the future (your prognosis), and what your treatment options are. 

Cancer of unknown primary (CUP) is only confirmed at the end of testing, when:
  • the primary cancer site cannot be found
  • tests show the cancer is not one that can be treated without knowing the primary site, such as a lymphoma, sarcoma or melanoma.

What you need to know

Cancer of unknown primary (CUP)

The most common way to describe cancers is by the part of the body they start in. This is called the primary cancer or primary site, e.g. lung cancer, bowel cancer or breast cancer.

In cancer of unknown primary or CUP, there is cancer in the body but the primary site cannot be found. The cancer that is present is secondary cancer in the body that has spread to another part of the body from where it originally started.

When cancer has spread to another part of the body, we call it ‘metastatic’ or ‘advanced cancer’.

Reasons why the primary cancer cannot be found may include:

  • The primary cancer is too small to be found but cells from it have spread and caused secondary cancer.
  • The body’s immune system killed or controlled the primary cancer but not the secondary cancer.
  • The primary cancer was removed during previous surgery for something else but had already spread.

Even though the primary site of the cancer cannot be found, tests can provide other important information. This includes the location of the secondary cancer in the body and type of cells in the cancer, which can help doctors to work out the most suitable treatment.

The cells in cancer of unknown primary are usually one of the following types:

  • adenocarcinoma
  • poorly differentiated carcinoma
  • squamous cell carcinoma
  • neuroendocrine carcinoma
  • undifferentiated neoplasm.
The way cancers are described and named can be confusing. Ask your doctor to explain what type of cancer you have and anything else you should know about it.

CUP subtypes

Cancer of unknown primary (CUP) is divided into two main groups:

  • specific CUP subtypes
  • non-specific CUP subtypes.

Specific CUP subtypes

In specific CUP subtypes, the type of cancer cells and the location of the secondary cancer in the body is very similar to a known cancer type, and the person can be treated as though they have that cancer type.

For example, a woman may have adenocarcinoma cells in the lymph nodes in her armpit (axilla) but no primary cancer can be found. Most breast cancers are adenocarcinomas, and they often spread to lymph nodes in the armpit, so this cancer can be assumed to be a breast cancer and treated as one even though the primary has not been found.

Non-specific CUP subtypes

In non-specific CUP subtypes, there is not enough information to work out what the cancer type is likely to be.

Treatment options for these subtypes, are based on test results which show how well the person is (ECOG performance score) and levels of a chemical in the blood called lactate dehydrogenase (LDH).

Cancer stage for CUP

For most types of cancer, the stage of the cancer is based on how large it is and how far it has spread when it is first diagnosed.

Doctors use the ‘TNM’ system for staging cancers where T stands for how big the primary cancer is, N stands for the number of lymph nodes involved and M shows whether the cancer has spread (or metastasised) from where it had first started.

Using this system, cancers are staged from 1 through to 4. The higher this number, the more advanced the cancer is. If the cancer has spread from where it started to another part of the body, it is usually a stage 4 cancer.

People with CUP have cancer that has spread but the primary site where the cancer started is not known. For this reason, it is difficult to stage a CUP.

CUP cancers are sometimes described as:

  • localised – limited to one part of the body
  • disseminated – spread more widely through the body.

What to ask or talk about

Talking about prognosis

Prognosis means what is likely to happen to you in the future because of your cancer. You may find it hard to talk about prognosis but it can help you make decisions about the treatment and care you want.

Everyone’s cancer is different, and everyone responds differently to treatment. Because of this, doctors can’t tell you exactly what will happen to you. Instead, they can give you the best information they have about what to expect.

Doctors work out prognosis based on statistics. These show what happens in large groups of people with cancer. They cannot predict what will happen to you or any other individual person. 

Checklists

Use our checklists to find helpful tips or questions to ask.

Next steps

Treatment planning

Your specialist will share information about you and your cancer with a multidisciplinary team (MDT) to decide the best treatment options for you.

You may need more than one type of treatment or have a choice of treatments. You may also need to see other specialists during treatment planning.

Dealing with your diagnosis

Getting a cancer diagnosis is very distressing for the person with cancer, and their carers, family and friends. Different people react in different ways. They can be upset and angry or just in shock. Many people find it difficult to take in all the information and understand what it will mean for them.

The situation can be especially difficult for people who get a diagnosis of advanced cancer. 

If you need to speak to someone about your diagnosis, you can call the Cancer Council on 13 11 20.

Where to get help

There are people you can talk to for more information or support.

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