Cancer of unknown primary (CUP) is a rare disease in which cancer cells are found in the body but the place the cancer began is not known.
Cancer can form in any tissue of the body. Normal cells grow and divide to form new cells as the body needs them. When normal cells grow old or get damaged, they die, and new cells take their place. Sometimes, this process goes wrong. New cells form when the body doesn't need them, and old or damaged cells don't die as they should. The buildup of extra cells often forms a mass of tissue called a growth or tumor. These tumors can be malignant (cancer).
The primary cancer (the cancer that first formed) can spread to other parts of the body. This process is called metastasis. Sometimes doctors find where the cancer has spread but cannot find where in the body the cancer first began to grow. Tests are done to find where the primary cancer began and to get information about where the cancer has spread. Identifying the primary cancer site is important because knowing its location and type often helps doctors plan the best treatment.
If the primary cancer is eventually found, the lung and pancreas are the most common primary cancer sites. Cancer of unknown primary also may be traced to the breast, prostate, colon, or rectum as the primary site.
Sometimes the primary cancer is never found. The primary cancer may not be found for one of the following reasons:
- The primary cancer is very small and grows slowly
- The body's immune system killed the primary cancer.
- The primary cancer was removed during surgery for another condition and doctors didn't know cancer had formed.
The sources for this information include the National Cancer Institute and the American Cancer Society's Cancer of Unknown Primary Detailed Guide.
Doctors can't always explain why one person gets cancer and another doesn't. Certain risk factors can increase a person's risk of getting cancer, and each type of cancer has different risk factors. Because the type of cancer is not known with cancer of unknown primary, it can be difficult to figure out which risk factors may have led to the disease.
Overall there are no risk factors that specifically raise the risk of cancer of unknown primary. However, research has found that more than half of people with cancer of unknown primary are current or former smokers, so smoking could be a risk factor for developing this type of cancer.
People concerned about their risk of developing cancer should talk with their doctor.
The symptoms of cancer of unknown primary depend on where the cancer has spread in the body.
Symptoms of cancer of unknown primary may include the following:
- A change in bowel or bladder habits, such as constipation, diarrhea, or frequent urination
- A cough that does not go away
- A fever for no known reason that does not go away
- A lump or thickening in any part of the body
- Hoarseness in the voice
- Loss of appetite
- Night sweats
- Pain that does not go away
- Unusual bleeding or discharge
- Weight loss for no known reason
Most often, these symptoms are not due to cancer. People with these symptoms should tell their doctor so any problems can be diagnosed and treated as early as possible.
If symptoms suggest cancer, the doctor will try to find out what's causing the problems. The doctor may order one or more of the following tests:
- Physical exam and history: The doctor will check for signs of disease, such as lumps or anything else that seems unusual.
- Urinalysis: This test checks the color of urine and its contents, such as sugar, protein, blood, and bacteria.
- Blood tests: The doctor sends blood to the lab to check the number of blood cells and to measure the amounts of certain substances released into the blood by organs and tissues in the body. A higher or lower than normal amount of a substance can be a sign of disease.
- Chest x-ray: X-rays of the organs and bones inside the chest can show whether cancer is present in that area of the body.
- Fecal occult blood test: This test checks stool (solid waste) for blood that can only be seen with a microscope. Small samples of stool are placed on special cards and returned to the doctor or a lab for testing. Because some cancers bleed, blood in the stool may be a sign of cancer in the colon or rectum.
- Biopsy: The doctor removes tissue from the body and sends it to a lab. The doctor in the lab looks at the tissue under a microscope for signs of cancer. The removal of tissue to look for cancer cells is called a biopsy. In most cases, a biopsy is the only sure way to tell whether cancer is present. How much tissue is removed and how the biopsy is done depends on what part of the body is being tested for cancer.
If cancer is found, the doctor will do more tests to try to find out the type of cancer and where it started. In some cases, the part of the body where cancer cells are first found helps the doctor decide which tests will be most helpful.
One or more of the following tests may be used to find out the type of cancer:
- Lab tests: The doctor may order one or more lab tests to look closely at the cancer cells. These tests may include staining the cells and looking at them under the microscope, using dyes to check for certain proteins, or looking for changes in genes or chromosomes in the cells.
- CT scan: An x-ray machine linked to a computer takes a series of detailed pictures of the inside of the body. The patient may receive contrast material by mouth or by injection into a blood vessel. The contrast material makes abnormal areas easier to see.
- MRI: A strong magnet linked to a computer is used to make detailed pictures of areas inside the body. Sometimes contrast material is given by injection into a blood vessel. The contrast material makes abnormal areas show up more clearly on the picture.
- PET scan: The patient receives an injection of a small amount of radioactive sugar. The radioactive sugar gives off signals that the PET scanner picks up. The PET scanner makes pictures of the sugar used by cells in the body. Cancer cells use sugar faster than normal cells, so areas with cancer look brighter on the pictures.
- Mammogram: An x-ray of the breast may be done if the doctor thinks that the cancer may have started in the breast.
- Endoscopy: The doctor uses a thin, lighted tube (endoscope) to look into the body. The endoscope may be passed through the mouth or nose, or may be inserted through an incision in the skin. The endoscope may have a tool to remove tissue or lymph node samples, which are checked under a microscope for signs of cancer.
- Tumor marker test: The doctor collects a sample of blood, urine, or tissue to measure the amounts of certain substances made by organs, tissues, or tumor cells in the body. Certain substances are linked to specific types of cancer when found in increased levels in the body. These are called tumor markers. The blood may be checked for the levels of alpha-fetoprotein (AFP), beta human chorionic gonadotropin, or prostate-specific antigen (PSA).
Sometimes, none of the tests can find the primary cancer site. In these cases, treatment may be based on what the doctor thinks is the most likely type of cancer.
The extent or spread of cancer is usually described as stages. The stage of the cancer is usually used to plan treatment. However, cancer of unknown primary has already spread to other parts of the body when it is found. Doctors will use the other information they know about the cancer to plan treatment.
At Huntsman Cancer Institute, cancer of unknown primary is treated by a team of specialists, including surgeons, medical oncologists (doctors who treat cancer with medicine), radiation oncologists (doctors who treat cancer with radiation), nurses, dietitians, and social workers.
Common treatment options for cancer of unknown primary include the following:
- Radiation therapy
- Hormone therapy
- Clinical trials
A patient with cancer of unknown primary may have a combination of treatments. The treatment that's right for each patient depends on many factors:
- Where the cancer began in the body and where it has spread
- The type of cancer cells that was found
- The number of organs with cancer in them
- The way the tumor cells look when viewed under a microscope
- The results of tests and procedures
- The patient's symptoms
- The patient's age and general health
The health care team can describe all of the treatment choices, the expected results of each, and the possible side effects. Because cancer therapy often damages healthy cells and tissues, side effects are common. Side effects may not be the same for each person, and they may even change from one treatment session to the next.
Surgery is a common treatment for cancer of unknown primary. A doctor may remove the cancer and some of the healthy tissue around it.
Even if the doctor removes all the cancer that can be seen at the time of the surgery, the patient may be given chemotherapy or radiation therapy after surgery to kill any cancer cells that are left.
Chemotherapy uses drugs to kill and control cancer cells throughout the body. Learn more about this treatment in our introduction to chemotherapy video.
Radiation therapy uses high-energy rays to kill cancer cells. Radiation therapy only affects cells in the treated area.
There are two types of radiation therapy used to treat cancer. Some people receive both types:
- External radiation: The radiation comes from a large machine outside the body. The machine aims beams of radiation at the cancer. Patients go to a hospital or clinic for treatment. This type of treatment uses computers to closely target the cancer, which protects healthy tissue.
- Internal radiation therapy (brachytherapy): The radiation comes from radioactive material usually contained in very small implants called seeds. The seeds are put near or directly into the cancer, using thin plastic tubes.
Hormones are substances produced by glands in the body and circulated in the bloodstream. The presence of some hormones can cause certain cancers to grow. Hormone therapy is a cancer treatment that removes hormones or blocks their action and stops cancer cells from growing. If tests show the cancer cells have places where hormones can attach (receptors), drugs, surgery, or radiation therapy are used to reduce the production of hormones or block them from working.
These studies discover and evaluate new and improved cancer treatments. Patients are encouraged to talk with their doctors about participating in a clinical trial or any questions regarding research studies. For more information, also visit HCI's clinical trials website.
When you or someone you love is diagnosed with cancer, concerns about treatments and side effects, hospital stays, and medical bills are common. You may also worry about caring for your family, work, or normal daily life.
There are several places you can go for support:
- Your health care team can answer your questions and talk to you about your concerns. They can help you with any side effects and keep you informed of all your treatments, test results, and future doctor visits.
- Our Patient and Family Support Services offer emotional support and resources for coping with cancer and its impact on daily life to HCI patients and their families.
- The Linda B. and Robert B. Wiggins Wellness-Survivorship Center offers many programs to increase the quality of life and well-being of HCI patients and their families.
Did You Know?
- About 2- 4% of all cancer patients have a cancer whose primary site is never identified.
- In recent years, microscopic and other diagnostic techniques have improved dramatically. For this reason, doctors can now determine the primary site in about four out of five cases first diagnosed as cancer of unknown primary.
- If the primary cancer is eventually found, the lung and pancreas are the most common primary cancer sites.