Merck Manual

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Quick Facts

Symptoms of Cancer


The Manual's Editorial Staff

Last full review/revision Jul 2021| Content last modified Jul 2021
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As cancer grows in your body, it can affect you in several ways. The cancer can:

For example, having a tumor near your bladder (the organ that holds your urine) can block your urine from coming out. Cancer inside your bones causes bone pain.

  • At first, cancer won’t cause any symptoms because it's just a tiny group of cells

  • As cancer grows, your symptoms will depend on where it's located

  • Some cancers can cause symptoms in parts of your body that aren’t close to your cancer

What are the symptoms of cancer?

Symptoms vary depending on the kind of cancer. Some cancers won't show symptoms until they have grown a lot. Others show symptoms at an early stage. Symptoms of cancer may include:


  • Most cancers are painless at first

  • As your cancer grows, you may have mild discomfort

  • Then, the pain gets worse as your cancer gets bigger

  • Not all cancers cause severe pain

Bleeding and blood clots

Cancer may cause bleeding inside your body, depending on where your cancer is located:

  • Cancer in your digestive tract can cause blood in your stool (poop)

  • Cancer in your urinary tract can cause blood in your urine

  • Cancer in your lungs can make you cough up blood

  • Cancer near a major artery can cause a hole in the artery that will bleed severely

  • Cancer in the bone marrow (the hollow insides of your bones, where blood cells are made) can stop your body from producing the cells that make blood clot

In advanced cancer, severe bleeding may cause death.

Many types of cancer increase the risk that you will develop blood clots in the veins in your legs. Blood clots in your leg veins sometimes break off and travel to a lung and block blood flow. This can cause serious difficulty breathing and sometimes death.

Weight loss and feeling weak

Muscle and brain symptoms

If cancer grows into or squeezes your nerves or spinal cord, you may have:

  • Pain

  • Weakness

  • Changes in your sense of feeling, such as tingling

If cancer starts in or spreads to your brain, you may have:

  • Confusion

  • Dizziness

  • Headaches

  • Feel sick to your stomach

  • Changes in your vision

  • Seizures

Lung symptoms

If cancer squeezes or blocks the airways in your lungs you may have:

  • Trouble breathing

  • Cough

  • Pneumonia (an infection that fills one or both lungs with fluid and mucus)

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