What’s the Difference Between a Cyst and a Tumor?

Until you can see your doctor, here are some signs of what that lump might be

Cyst on hand

Did you find a lump on your body and now you’re wondering what to do next? First, contact your doctor. Second, try not to panic.


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Many lumps are fluid-filled masses, or cysts, which are usually harmless. Other lumps may be solid masses that are called tumors. It’s important to remember that not all tumors are cancerous.

Breast imaging specialist Laura Shepardson, MD, and plastic surgeon Raymond Isakov, MD, discuss cysts and tumors, and how to tell the difference.

What are cysts?

A cyst is a sac that usually contains watery, thickened fluid. Some cysts are even filled with a cheesy, goopy or waxy-like substance. There are many types of cysts. Although they can be any size, most cysts are round, smooth and easy to roll around.

How do cysts form? These steps lead to a cyst:

  1. Something blocks a gland or drainage system in your body.
  2. The fluid or material in the gland or drain has nowhere to go, so it builds up. (Picture a dam blocking a river.)
  3. Your body recognizes the blockage and forms a scar-tissue wall (sac) around the fluid or material.
  4. The scar tissue holds the fluid or material like a water balloon, forming a cyst.

Cysts may form in or on:

  • Glands and ducts, such as those in your breasts.
  • Internal organs, like your ovaries, kidneys or liver.
  • Joints, like your wrists or knees.
  • Skin, often from conditions like acne or folliculitis.

Why do people develop cysts?

Depending on their locations, cysts form for a variety of reasons. For example, cysts may happen because of a medical condition, such as polycystic kidney disease. Cysts may also be normal, like those that form on ovaries during ovulation.

“Similarly, many women develop cysts in their breasts because their hormones are constantly changing during the course of their menstrual cycles,” says Dr. Shepardson.

Lastly, cysts may also show up in the body with no obvious cause.

Can cysts turn into cancer?

If you have a cyst in your body, the chance of it being cancer is extremely low.

“There are only a few known cases of cysts turning into cancer,” says Dr. Isakov. “The overwhelming majority of cysts are harmless. But if it’s causing you pain or it gets infected, we can remove them.”

If you or your healthcare provider feels a lump in your breast, the next step typically involves imaging of the lump through a mammogram and ultrasound. If the radiologist sees a cyst, rest easy.

“Cysts in the breasts are benign,” says Dr. Shepardson. “They don’t turn into cancer, and they don’t increase your risk of getting breast cancer. In fact, we usually leave cysts alone unless they are causing symptoms like pain or they are getting large, in which case we can use a needle to remove the fluid.”


What are tumors?

Your body’s cells grow and divide at a set pace. Some cells die, while new ones form. If something goes wrong with this process, a tumor can develop.

“A tumor is a mass or lump of tissue that forms when cells grow and divide too quickly,” explains Dr. Isakov. “Many tumors are benign. That means they aren’t cancer, and they won’t spread.”

Some of the most common types of benign tumors include:

  • Lipomas: These fatty tumors are slow-growing and very common, affecting at least 1 in every 1,000 people. You might find a lipoma on your back, torso, shoulders, neck or arms. “We may need to perform a biopsy to be sure it’s a lipoma and not another type of growth,” says Dr. Isakov. “Lipomas can run in families, so if your parent had them, you’re more likely to have them, too.”
  • Fibroadenomas: This is the most common type of benign breast tumor. If you or your healthcare provider feels a lump in your breast and a solid mass is seen on your mammogram and ultrasound, it may very well be a fibroadenoma. “The good news is that fibroadenomas can often be left alone, requiring no treatment,” notes Dr. Shepardson.

How can you tell the difference between a cyst and a tumor?

Only a medical professional can tell you for sure what that lump or bump is. “Even if you’re pretty sure it’s a cyst, your doctor needs to check it out,” cautions Dr. Isakov.

Identifying a cyst

If you have a cyst, it might:

  • Feel sore or tender to the touch.
  • Have a pore, dot or blackhead in the center.
  • Leak yellowish or green fluid.
  • Look red or irritated.
  • Move around under your skin when you press on it.

Identifying a tumor

A lump could be a tumor if it:

  • Feels firm to the touch, almost like a pebble or stone.
  • Shows up suddenly or seems to be growing rapidly.
  • Doesn’t move when you press on it.

Signs to watch for

See your doctor right away if your lump or bump is:

  • Fast-growing or seems to be changing in shape.
  • Located in your armpit, groin or neck. Lumps in these areas could signal an infection or tumor in your lymph nodes, which act like filters for your immune system.
  • Red or feels hot when you touch it, which could be a sign of an infection.


Again, if you notice a lump in your breast, bring it to the attention of your healthcare provider immediately. Although most breast lumps aren’t cancerous, your doctor may want to examine your breast and/or recommend a mammogram and ultrasound to get a better look at it.

Tests that diagnose cysts or tumors

Your doctor will probably order at least one imaging test to look at that lump or bump. You may need:

  • Ultrasound: This test uses sound waves to determine if the mass is filled with fluid or is solid.
  • CT scan: This detailed X-ray produces 3D images of the inside of your body.
  • MRI: Magnets and a special computer take pictures of your internal organs and structures without radiation.
  • Mammogram: X-ray of your breast, which looks for any abnormality in the breast tissue. (Learn how 3D mammograms can help find hidden cancers.)

Next steps after tests

If your test results reveal a cyst, your doctor may offer to drain it with an in-office procedure. But in many cases, cysts don’t need draining unless they’re bothering you.

Sometimes, your doctor may perform a biopsy to determine exactly what the lump is. Usually, doctors use a special needle to take a small sample of the growth. They send the sample to a lab for testing and then let you know the results.

Don’t wait — get that lump checked out

Finding a new lump or bump can be alarming. But don’t let worry or fear stop you from seeing your healthcare provider. They can reliably find out what that lump is and help you get the appropriate treatment if you need it.


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