There are many tests that can help your doctor find the primary source of carcinoma of unknown primary origin (CUP). Your doctor may order several of these tests to help determine the source of your cancer.
If you have symptoms that could mean cancer, your doctor will take a sample of your blood to measure the level of certain substances in your blood:
Blood cell count. Changes in the numbers of certain blood cells may mean that cancer has spread to your bones and bone marrow cells.
Liver, kidney, and bone function. If any of these tests are abnormal, your doctor will check further to see if any of these organs is the primary site of the cancer.
Tumor marker tests. Some kinds of cancer release proteins or special markers into the blood. If any of these markers is present in your blood, your doctors may be able to tell what kind of cancer you have. For example, a man may have high prostate-specific antigen (PSA) levels in his blood. This might mean that the cancer may have started in his prostate gland.
Imaging tests show doctors what is happening on the inside of your body. You may undergo one or more of these imaging tests:
X-rays. Often a doctor takes X-rays of the lungs, heart, bones, or digestive tract to determine where the cancer started.
Ultrasonography. This test uses sound waves to look for problems in your internal organs. Like sonar on a submarine, the machine sends out sound waves that bounce off body parts and send back an image. A computer then uses the signals to create an image of your body. Ultrasound images can help your doctor spot growths. This test can also help them decide if the growth is a cyst or a solid tumor. A cyst is a fluid-filled sac that is probably not cancer. A solid tumor is more likely to be cancer.
Computed tomography, or CT scan. In this test, an X-ray beam moves around your body while a machine takes pictures from many angles. These pictures are then combined by a computer, giving your doctor detailed cross-section images of your body.
Magnetic resonance image (MRI). An MRI uses magnets and radio waves to take pictures of the inside of your body. In many cases, MRIs can reveal more details about the internal organs than other imaging tests.
Positron-emission tomography, or PET. Cancer cells use glucose (sugar) differently than normal cells. This test uses a radioactive sugar solution to produce images of how the different cells in your body use glucose for fuel. Then, a special type of scanner takes pictures to see which cells are using the most glucose, since cancer cells typically need more glucose than normal cells.
Bone scan. This is a test where a radioactive dye is injected into your veins. The dye will travel to and be taken up by your bones. Cancerous growths in bone take up the dye differently than normal bone.
During a biopsy, your doctor removes tissue samples from areas that might be cancerous. A pathologist then examines the samples under a microscope. There are several types of biopsies that may be done to try to determine where the cancer started. Here are some of them:
Fine needle aspiration. Your doctor uses a thin needle to remove some fluid or a small amount of tissue from the tumor.
Core needle biopsy. The doctor can remove more tissue in this test. The needle is wider than the one used in a fine needle aspiration.
Paracentesis or thoracentesis. For paracentesis, your doctor uses a needle to remove fluid from your abdomen. For thoracentesis, your doctor uses a needle to remove fluid from the area around your lungs. The pathologist can determine if the fluid contains cancer cells.
Bone marrow aspiration/biopsy. Your doctor will remove a small amount of bone marrow fluid and a piece of bone tissue. The doctor uses a special needle to take these samples, usually from your hip bone.
Excisional biopsy. A surgeon removes the entire tumor in one piece. Lymph nodes that could contain cancer may be removed as well. A pathologist examines the tissue for signs of cancer.
Incisional biopsy. The surgeon takes out only a part of the tumor. This strategy is used if the tumor is so large that removing the whole tumor may cause complications. A pathologist examines the tissue for signs of cancer.
Diagnostic pathology tests. The pathologist uses a range of tests to help find signs of cancer and determine the source. The pathologist stains the tissue samples to find tumors such as sarcomas, melanomas, and lymphomas. Other special stains help identify tumors or cells that may have come from the testicle, prostate, breast, thyroid gland, or colon. In addition, the pathologist may view the sample under an electron microscope. This special microscope can show more precise details that give clues about the origin of the cells. Finally, the pathologist may use chromosomal analysis. In this test, the pathologist looks for any genes that may have problems. Different damaged genes may lead to different kinds of tumors.
Your doctor may ask you to collect a small sample of your urine for a test called a urinalysis. This test may reveal evidence of kidney, bladder, or prostate cancer. The doctor may also check your stool for blood, which may suggest cancer of the digestive tract.