Cancer of unknown primary (CUP) is the term used to describe a metastatic cancer (cancer that has spread) with an unknown starting point.
CUP is the ninth most common cancer in men and the seventh most common in women. It is the third most common cause of cancer death in Australians, causing about 10% of cancer deaths.
Usually, when cancer spreads the secondary cancer cells look like abnormal versions of the primary cancer cells (in the tissue where the cancer began) eg. if breast cancer spreads to the lungs, the metastatic tumour in the lung is made up of cancerous breast cells (not lung cells) and is then described as metastatic breast cancer (not lung cancer). If it is not possible to identify the type of cancer cells the diagnosis is CUP.
Incidence and mortality
There are around 2897 new cases of CUP each year in Australia. The risk of CUP before the age of 85 is 1 in 49 for men and 1 in 69 for women.
In 2007, there were 2344 deaths from CUP.
Screening
There is no screening method for CUP.
Symptoms and diagnosis
Some people with metastatic cancer have no symptoms, but common symptoms include:
- breathlessness or discomfort in the chest
- bone pain, back pain
- swelling and discomfort in the abdomen, fluid collecting in the abdomen (ascites), yellowing of the skin and eyes (jaundice)
- swollen lymph glands such as those in the neck, underarm, chest or groin
- general symptoms such as weight loss, headaches, no appetite, feeling extremely tired.
Tests are ordered to ensure that cancers which are still curable or treatable, even when spread, are not missed. Tests may include a biopsy, physical examination, x-ray and blood test. Further diagnostic tests are done, based on the site of the secondary cancer/s and any ‘clues’ as to where the cancer may have started.
Diagnostic tools include blood biochemistry (checking for markers for cancers such as breast or prostate that could be treated with hormones), faecal occult blood testing, urinalysis, histopathogical review of all biopsy material using immunohistochemistry, CT of the abdomen and pelvis, mammography and PET scan.
Staging
Staging systems differ for different cancer types. For most cancers there are four stages, with stage 1 being an early cancer and stage 4 an advanced cancer. Because a CUP has already spread, it must be stage 2 or higher. If it has spread to another body organ, it is a stage 4 cancer.
Causes
For patients with CUP the primary cancer site is not known, therefore it is difficult to identify risk factors. Smoking may be an important risk factor, as more than half of CUP patients have a history of smoking. Other risk factors may include older age, diet, alcohol and obesity – common risk factors for many cancers.
Prevention
Since the causes of CUP are unknown, there is no prevention advice specific to this disease. Having a generally healthy lifestyle – including not smoking, maintaining a healthy diet and weight and limiting alcohol consumption – may be protective.
Treatment
For most cancers, treatment is determined by the type of cancer and depends on correct diagnosis and staging. Because the primary cancer is unknown, there is no standard treatment for CUP.
The main treatment used for CUP is broad spectrum chemotherapy unless the unknown primary is in a very specific area. For example, neck nodes are usually treated like head and neck cancer, axillary node presentations are treated in the same manner as breast cancers, and peritoneal presentations are treated like ovarian cancer.
Prognosis
For most individuals diagnosed with cancer prognosis depends on the type and stage of cancer, as well as their age and general health at the time of diagnosis. CUP is not diagnosed until a patient has metastatic cancer, and treatment is difficult because the primary cancer type can not be determined. Five year survival for people in Australia diagnosed with CUP is 9%.
For more information, contact Cancer Council Helpline on 13 11 20 (cost of a local call).