Cancer of unknown primary

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Prognosis and survival for cancer of unknown primary

If you have cancer of unknown primary (CUP), you may have questions about your prognosis. A prognosis is the doctor’s best estimate of how cancer will affect a person and how it will respond to treatment. Prognosis and survival depend on many factors. Only a doctor familiar with your medical history, the type and characteristics of your cancer, treatments chosen and response to treatment can put all of this information together with survival statistics to arrive at a prognosis.

A prognostic factor is an aspect of the cancer or a characteristic of the person that the doctor will consider when making a prognosis. The following are prognostic factors for CUP.

Favourable-risk or poor-risk CUP

Doctors will decide if CUP is favourable risk or poor risk.


Favourable-risk CUP is identified based on where the cancer is found in the body and based on biopsy results. The following are considered favourable-risk CUP:

  • neuroendocrine carcinoma
  • adenocarcinoma in the lymph nodes under the arm in women
  • adenocarcinoma in the peritoneal cavity in women
  • squamous cell carcinoma in the lymph nodes in the neck or in the groin
  • poorly differentiated carcinoma in the middle (or midline) of the body
  • CUP in a bone in men who have a high prostate-specific antigen (PSA) level
  • CUP of colorectal cancer type
  • CUP that is only forming one metastasis

Poor-risk CUP includes all cancers that are not part of the favourable risk group. It includes poorly differentiated and undifferentiated tumours. These types of CUP do not respond as well to chemotherapy. Most people diagnosed with CUP have poor-risk disease.

The following factors indicate poor prognosis within poor-risk CUP:

  • adenocarcinoma in the liver and other organs
  • adenocarcinoma cancer cells found in a buildup of fluid in the abdomen (called malignant ascites)
  • CUP in several different places in the brain
  • CUP in several parts of the lungs or the lining of the lungs
  • CUP in a bone in men who do not have a high PSA level

Where the cancer has spread

Prognosis depends on where the cancer has spread, or metastasized, and how many different places it has spread to.

People who only have cancer in the lymph nodes have a better prognosis than people who have cancer in their internal organs (such as the liver or lungs).

People who have cancer in several different places (such as the liver, lungs and bone) have a poor prognosis.

People with cancer that has spread to several different parts of the brain have a poor prognosis.

People with cancer cells in a buildup of fluid in the abdomen (called malignant ascites) have a less favourable prognosis.

Performance status

Performance status is a measure of how well a person can do ordinary tasks and carry out daily activities (such as bathing, dressing or walking). There are different performance status scales used, but generally the more active you are, the better your performance status.

A person diagnosed with CUP who has a good performance status has a more favourable prognosis than someone who has a poor performance status.

Lactate dehydrogenase (LDH) levels

People diagnosed with CUP who have normal lactate dehydrogenase (LDH) levels in their blood have a more favourable prognosis than people with high levels of LDH.


Women with CUP tend to have a more favourable prognosis than men with CUP.

peritoneal cavity

The space between the parietal peritoneum (the membrane that lines the walls of the abdomen and pelvis) and the visceral peritoneum (the membrane that covers and supports most of the abdominal organs).

prostate-specific antigen (PSA)

A protein made by the prostate that is normally found in the semen and blood. Higher amounts of PSA may be found in the blood of men who have prostate cancer, benign prostatic hyperplasia (BPH) or inflammation of the prostate.

PSA can be used as a tumour marker. It is used to monitor a man’s response to treatment for prostate cancer, or to see if prostate cancer has come back (recurred) after treatment.

lactate dehydrogenase(LDH)

An enzyme that is involved in energy production in cells.

LDH is normally found in the blood and other body tissues. Higher levels of LDH may indicate tissue damage or the presence of cancer cells. LDH may be used as a tumour marker or to monitor a person’s response to treatment for certain cancers.

Also called lactic acid dehyrodgenase.