What Is Cancer of Unknown Primary?

When doctors find cancer cells, they can often tell which part of the body had them first. It could be a certain organ, type of tissue, or part of your blood. If it can’t be pinpointed, then you have what’s called a cancer of unknown primary (CUP).

This type of cancer may not be found until it has spread to your lymph nodes, liver, lungs, bones, or skin. Although treatments may not cure CUP, being part of a clinical trial may help.

What Are the Causes?

All cancers happen because of changes called mutations in a cell’s DNA. This is the genetic material inside each of your cells that controls how they behave. In most cases, multiple mutations need to happen before a cell becomes cancerous.

Doctors believe the DNA changes that cause CUP aren’t passed down through families, but happen during your lifetime. It could be because you’ve been exposed to things that are known to cause cancer, like radiation, tobacco smoke, or chemicals.

But these harmful changes can also take place for no clear reason. Many people with CUP are at a healthy weight, exercise often, and eat right. If you’ve been diagnosed with CUP, it’s important to note that there’s likely nothing you could have done differently to prevent it.

What Are the Symptoms?

The symptoms of CUP will vary, based on where the cancer is in your body. Some signs include:

There’s also a chance you won’t have symptoms. Some people only learn they have CUP after a medical test for a different reason.

How Is CUP Diagnosed?

Your doctor will give you a thorough exam and ask about any symptoms you have. She’ll also want to hear about any past health problems and if any cancer runs in your family.


Tests of your blood, pee, and poop can provide your doctor with more information. So can the following:

Imaging test: This could include X-rays, an MRI, CT scan, or ultrasound.

Endoscopy: Your doctor may put a very thin tube into your body via your mouth, nose, bottom, or a tiny incision in your skin. A camera on the end allows her to see a tumor up close.

Biopsy: Based on where the tumor is, your doctor will get a sample of cells, fluid, or bone marrow. This will be sent to a lab and looked at under a microscope. There are also new genetic tests that can pinpoint where in your body the cancer started.

What’s the Treatment for CUP?

Most cancers are “staged.” This explains where they are in your body and how much they’ve spread. It also helps doctors devise a treatment plan. This can’t be done with CUP, since it’s already spread by the time it’s found.

Instead, your doctor will decide how to treat you based on where the cancer is, what the cancer cells look like under a microscope, your symptoms, your test results, and whether this is the first time you’ve had cancer or if it has returned.

Treatment is usually chemotherapy, and depends on if a primary site, or at least a primary tissue can be identified. Your treatment could include:

Chemotherapy: You’ll be given very strong drugs that destroy cancer cells. These may be given to you through an IV, or you could take a pill by mouth.

Surgery: Your doctor will remove the cancer plus some healthy tissue around it.

Radiation therapy: High energy X-rays or other forms of radiation can be used to kill cancer cells. This may be given to you through a machine, or the radiation can be put into your body through a needle, wire, or tiny sealed “seed.”

Hormone therapy: If hormones are believed to play a part in your cancer, your doctor will try to reduce the amount that your body makes or keep the ones it does make from working. Sometimes this is done with drugs, but surgery and radiation can be used, too.


Targeted therapy: Drugs or other substances can attack cancer cells without harming the rest of your body.

Immunotherapy (biologic therapy): This treatment boosts your immune system in general or uses it to attack cancer cells.

Clinical trial: In some cases, being part of a clinical trial may be your best choice. These studies test new cancer drugs and treatments to see if they work as well or better than treatments already in use.

CUP is different in each person. How well treatment works is hard to predict.

Make sure to speak to your doctor. Since she’s aware of your cancer, test results, and health in general, she’ll have a better idea about your chance of recovery.

WebMD Medical Reference Reviewed by Sabrina Felson, MD on May 15, 2019


National Cancer Institute: “Carcinoma of Unknown Primary Treatment (PDQ®) --Patient Version.”

American Cancer Society: “Do We Know What Causes a Cancer of Unknown Primary?” “Can a Cancer of Unknown Primary Be Prevented?” “Signs and Symptoms of a Cancer of Unknown Primary,” “Targeted Therapy for Cancer of Unknown Primary,” “Survival Statistics for Cancer of Unknown Primary,” “What is cancer immunotherapy?”

Memorial Sloan Kettering Cancer Center: “Cancer of Unknown Primary Origin.”

Cancer.net/American Society of Clinical Oncology: “Unknown Primary: Treatment Options.”
The University of Texas M.D. Anderson Cancer Center: “Cancer of Unknown Primary Diagnosis.”

Cleveland Clinic: “Carcinoma of Unknown Primary.”

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