Cancer starts when cells change (mutate) and grow out of control. The changed (abnormal) cells often grow to form a lump or mass called a tumor. Cancer cells can also grow into (invade) nearby areas. They can spread to other parts of the body, too. This is called metastasis.

Most of the time, doctors can find the place in your body where cancer cells first started to grow. This is called the primary site. In carcinoma of unknown primary (CUP), doctors can't tell where the cancer first started. CUP has already spread to other places by the time it's diagnosed. Other names for CUP are unknown primary cancer (UPC) or occult primary tumor.

CUP can affect many organs in the body. But the organ in which it first started may never be known. The most common places CUP spreads to and where it's often first found are the:

• Lymph nodes in your neck, arms, or groin.
• Lungs.
• Liver.
• Brain.
• Bones.

Sometimes, after many tests, doctors will be able to find where the cancer started. Then they will rename the cancer for that site.

A risk factor is anything that may increase your chance of having a disease. The exact cause of someone's cancer may not be known. But risk factors can make it more likely for a person to have cancer. Some risk factors may not be in your control. But others may be things you can change.

Doctors don't know the why, how, or where of CUP. So it's hard to identify risk factors for it. But risk factors include those that make you more likely to get all types of cancer, such as:

• Older age.
• Tobacco and nicotine use.
• Poor diet.
• Being at a higher weight.
• Not being physically active.
• Too much sun exposure.
• Family history of cancers, such as those of the breast or colon.
• Exposure to radiation or certain chemicals.
• Genetic syndromes that are associated with increased risk for specific cancers.

These risk factors are linked to many kinds of cancer. So managing them may help reduce the risk for CUP. Talk with your doctor about your risk factors for cancer and what you can do about them.

You may be able to help prevent CUP by lowering your overall cancer risk. Here are some things you can control to help reduce your risk of cancer:

• Don't smoke or use any form of tobacco or nicotine.
• Stay away from other people's smoke.
• Eat more fruits, vegetables, and whole grains.
• Limit alcohol.
• Exercise regularly.
• Get to or stay at a healthy weight for you.
• Use sunscreen.
• Get the human papillomavirus (HPV) and hepatitis B vaccines as recommended by your doctor.

There is no sure way to prevent CUP. But you should get routine physicals and the recommended cancer screening tests. Screening tests are done to check for disease in people who don't have symptoms.

These steps can help to find precancer changes so they can be treated before they become cancer. They also can help find cancer early, when it's small and easier to treat.

Symptoms of CUP depend on where it is in your body. It can cause:

• Swollen lymph nodes.
• Pain in one part of the body that doesn't go away or that gets worse.
• Sudden fracture of a bone.
• A lump that gets bigger over time.
• Stomach pain or fullness.
• No desire to eat.
• Unexplained weight loss.
• A change in the way your bladder or bowels work.
• A fever that doesn't go away.
• Tiredness or weakness.
• Night sweats.
• Tumors on your skin.
• Shortness of breath or a cough that doesn't go away.
• Cough or hoarseness.
• Unusual bleeding or discharge.
• Low red blood cell levels (anemia).
• Confusion, headache, blurry vision, and seizures.

Many of these may be caused by other health problems. Still, it's important to see a doctor if you have these symptoms. Only a doctor can tell if you have cancer.

Your doctor will ask you about your health history, symptoms, risk factors, and family history of disease. A physical exam will be done. If your doctor thinks you have cancer, tests will be used to try to find the primary site, the place where the cancer started.

You may have one or more tests, including:

• Urine, plasma, and blood tests.
• CT scan.
• MRI.
• Ultrasound.
• PET scan.
• Mammogram.
• Endoscopy exams.
• Biopsy.

Sometimes the only sign that someone has cancer is a single tumor in their body. This tumor may be very far from where the cancer cells first grew. A biopsy may help find the source of the cancer. To do a biopsy, tiny pieces of tissue are taken out and tested for cancer. Lab tests may be able to show what kind of cancer cells they are. Knowing the primary site helps your doctors know how to best treat the cancer.

After a diagnosis of CUP, you may have other tests. These can help your doctors learn more about the cancer. If the doctors aren't able to figure out where the cancer started, they may decide that further testing won't be helpful.

Treatment of CUP depends on where the cancer is and the results of lab tests done on the cancer cells that were removed during the biopsy. The goal of treatment may be to control the cancer or help ease problems caused by the cancer. Talk with your care team about your treatment choices, the goals of treatment, and what the risks and side effects may be.

Types of treatment for cancer are either local or systemic. Local treatments remove, destroy, or control cancer cells in one area. Surgery and radiation therapy are local treatments. These aren't often used for CUP because the cancer has already spread before it's found.

Systemic treatment is used to destroy or control cancer cells that may have traveled around your body. When taken by pill or injection, chemotherapy, immunotherapy, and targeted therapy are systemic treatments. You may have just one treatment or a combination of treatments.

Treatment for CUP is started only after doctors have searched for the primary cancer. Treatment may include:

• Chemotherapy.
• Targeted therapy.
• Immunotherapy.
• Hormone therapy.
• Radiation therapy.
• Surgery.

Talk with your doctors about your treatment options. Make a list of questions. Think about the benefits and possible side effects of each option. Talk about your concerns with your doctor before making a decision.

Cancer treatment such as chemotherapy and radiation therapy can damage normal cells. This can cause side effects like hair loss, mouth sores, and vomiting.

Talk with your doctor about side effects linked to your treatment. There are often ways to manage them. There may be things you can do and medicines you can take to help prevent or control many treatment side effects.

Many people feel worried, depressed, and stressed when dealing with cancer. Getting treatment for cancer can be hard on your mind and body. Keep talking with your care team about problems and concerns you have. Work together to ease the effect of cancer and its symptoms on your daily life.

Here are some tips:

• Talk with your family or friends.
• Ask your care team or social worker for help.
• Speak with a counselor.
• Talk with a spiritual advisor, such as a minister or rabbi.
• Ask your care team about medicines for depression or anxiety.
• Keep socially active.
• Join an in-person or online cancer support group.

Cancer treatment is also hard on the body. To help yourself stay healthier, try to:

• Eat healthy foods, with a focus on high-protein foods.
• Drink plenty of water, low-sugar fruit juices, and other liquids.
• Keep physically active.
• Rest as much as needed.
• Talk with your care team about ways to manage treatment side effects.
• Take your medicines as directed by your team.

Your doctor will talk with you about when to contact them. You may be told to contact them if you have:

• New symptoms, or symptoms that get worse.
• Signs of an infection, such as a fever.
• Side effects of treatment that affect your daily function or don't get better with treatment.

Ask your doctor what signs to watch for and when to contact them. Know how to get help after office hours and on weekends and holidays.

• Cancer of unknown primary (CUP) is cancer that cannot be linked to a primary site, or the exact part of the body where it first started.
• CUP has always spread before it's first found.
• Routine screening and following cancer prevention guidelines can help decrease your risk of CUP and many other kinds of cancer.
• Symptoms of CUP depend on where the cancer is in your body.
• Imaging tests, lab tests, and a biopsy are usually needed to diagnose CUP.
• Many kinds of treatment are used, including surgery, chemotherapy, radiation therapy, targeted therapy, hormone therapy, immunotherapy, and other medicines.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your doctor tells you.
• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your doctor gives you.
• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your doctor if you have questions.