A tumor is a mass of abnormal tissue caused by an overgrowth of cells. Benign tumors don’t always require treatment, but they do call for careful monitoring.

There are two main types of tumors. Benign tumors are noncancerous and malignant tumors are cancerous. Other words for ‘tumor’ are lesion, polyp, and neoplasm.

Some types of benign tumors, such as colon polyps, have the potential to progress into cancer over time.

Read on to learn the different types of benign tumors and which ones are more likely to become malignant.

Tumors form when cells start dividing too rapidly and stop dying off as they should. The big difference is that benign tumors can’t invade other parts of the body as malignant ones can.

About benign tumors

Benign tumors have smooth, distinct borders and are typically slow growing. They can get bigger, but they grow in one place without spreading.

While they don’t always cause problems, they can become harmful if:

  • they grow so big that they push on nearby structures or organs
  • they cause pain or discomfort
  • they release hormones that affect body systems
  • you’re not comfortable with how they look

About malignant tumors

Malignant tumors have irregular borders and tend to grow faster than benign tumors. They’re made up of cancer cells and can invade nearby tissues.

Cells can break off and spread through the bloodstream or lymph system. Then, they can form new tumors in distant parts of the body, a process called metastasis.

Diagnosing benign vs. malignant tumors

Your doctor may have some idea whether a tumor is cancerous based on a physical examination and imaging tests. But you’ll need a biopsy to know for certain.

By examining the tissue under a microscope, a pathologist can identify features of the tumor, including whether it contains cancer cells.

Is there a difference between a cyst and a tumor?

A cyst is not a tumor. A tumor is a solid mass of tissue that develops from an overgrowth of cells. A cyst is a closed sac of tissue filled with fluid, air, pus, or other material. Most cysts are benign. Cysts form for various reasons, including infection, blocked ducts, or injury.

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Many types of benign tumors can grow just about anywhere on the body, including:

  • Adenomas: These tumors start in epithelial tissue, such as colon polyps in the GI tract.
  • Fibromas: Growths, such as uterine fibroids (also called leiomyomas or myomas), usually form in fibrous connective tissue.
  • Hamartomas: These tumors are an abnormal mix of cells and tissues from the surrounding area. They tend to form in the lungs, heart, skin, brain, or breast.
  • Hemangiomas: Caused by an abnormal buildup of blood vessels, these growths usually develop on the skin and internal organs.
  • Lipomas: These soft tissue tumors usually develop in the fatty tissue just under the skin.
  • Nevi: These are moles on the skin.
  • Osteochondromas: These bone tumors form from an overgrowth of cartilage and bone.
  • Papillomas: These tumors grow in tissue linking skin and organs, such as intraductal papilloma of the breast.

Colon polyps are a prime example of benign tumors that can turn malignant. Colon and rectal cancer (colorectal cancer) often starts with polyps.

According to Harvard Health Publishing, it can take 7–10 years or even longer for an adenoma to turn cancerous, but you may not have symptoms until it’s advanced. While only 5% of adenomas progress to cancer, doctors have no way to predict who’s at risk.

Removing polyps found during a colonoscopy can help prevent colorectal cancer from developing.

Moles are generally harmless, but an abnormal mole can develop into melanoma. A sign this may be happening is that the mole is changing in size, shape, color, or texture. Melanomas are typically asymmetrical and have irregular borders.

Cervical dysplasia describes growths in the cervix that are a precursor to cervical cancer. It can happen faster, but the transition to cervical cancer can take 10–30 years. There are usually no symptoms, so a pap test may provide the first clue. Removing the abnormal tissue can help prevent cervical cancer from developing.

Cells go through stages on their way to becoming cancerous. Hyperplasia is when there’s an unusually high number of cells, but they still look normal under a microscope.

Dysplasia means the cells no longer look normal. Dysplasia can be mild, moderate, or severe. The more abnormal the changes, the more likely it will turn into cancer. Doctors sometimes call this “precancer.”

Your doctor may recommend a schedule of visits to look for these changes. This is known as “active surveillance.” Active surveillance usually means regular visits with your doctor or having repeated tests to check for changes and if cancer has developed.

Most benign tumors are slow growing and may never need treatment. However, depending on the cancer, a doctor may choose to treat a precancer with surgery or another removal method before active surveillance to prevent or delay a malignant tumor from developing.

Treatment depends on the type, size, and location of the tumor. Some reasons you may need to surgically remove a benign tumor include:

  • it’s taking up space in the brain or spinal cord
  • it’s pressing on an organ, nerves, or blood vessels
  • it’s weakening a bone
  • it’s replacing healthy tissue with abnormal tissue as it grows
  • it’s causing pain or discomfort
  • you’d like it removed for cosmetic reasons

Once removed, benign tumors don’t usually recur. Other treatments for benign tumors may include topical medications or radiation therapy.

If you have a new growth on your body, it’s best to see a doctor and find out if it’s benign or malignant. Many benign tumors are harmless, but they can cause problems if they grow too large or affect major organs or vessels.

There are treatments for benign tumors, including surgical removal.

Some benign tumors can become malignant over time. That’s why it’s important to schedule periodic examinations. Let your doctor know if a benign tumor starts to change in shape, size, color, or texture.