When you hear the word tumor, you likely think of cancer. But, in fact, many tumors aren’t cancerous.

A tumor is a cluster of abnormal cells. Depending on the types of cells in a tumor, it can be:

  • Benign. The tumor doesn’t contain cancerous cells.
  • Premalignant or precancerous. It contains abnormal cells that have the potential to become cancerous.
  • Malignant. The tumor contains cancerous cells.

In this article, we’ll take a closer look at the key differences between benign and malignant tumors and how they’re diagnosed and treated.

Benign tumors aren’t cancerous. They won’t invade surrounding tissue or spread elsewhere.

Even so, they can cause serious problems when they grow near vital organs, press on a nerve, or restrict blood flow. Benign tumors usually respond well to treatment.

The most common types of benign tumors include the following:


Adenomas, or polyps, develop in glandlike cells in epithelial tissue, a thin layer of tissue covering glands, organs, and other structures.

Treatment depends on location and size. Some colon polyps are adenomas and should be removed in case they become malignant.


Fibroids grow in fibrous tissue. Uterine fibroids are common, affecting 20 to 80 percent of women by age 50. They don’t necessarily need treatment. If they’re causing pain or other problems, a doctor can surgically remove them.


Hemangiomas are a type of tumor that’s made up of extra blood vessels. They’re the most common tumors in children. They tend to occur more often on the skin and liver.

On the skin, a hemangioma may initially appear to be a red birthmark. Then, over time, it will start to form a red lump.

Although they should be monitored, hemangiomas typically don’t cause problems and usually fade away without treatment.


Lipomas are slow-growing tumors that form in fatty tissue under the skin. They can occur anywhere, but particularly the neck, shoulders, armpits, or trunk.

They’re most common between the ages of 40 and 60. Treatment isn’t always necessary, but you can have them removed if they bother you.

Benign tumors don’t necessarily turn into malignant tumors. Some have the potential, though, to become cancerous if abnormal cells continue to change and divide uncontrollably.

These terms describe some unusual characteristics of potentially premalignant tumors:

  • Hyperplasia. Normal-looking cells are reproducing faster than normal.
  • Atypia. Cells appear slightly abnormal.
  • Metaplasia. Cells look normal but aren’t the type of cells usually found in this area of the body.

Since it’s difficult to know which tumors will progress, the following types of masses must be carefully monitored or treated:

  • Dysplasia. Cells appear abnormal, are reproducing faster than normal, and aren’t arranged normally.
  • Carcinoma in situ. Cells are extremely abnormal but haven’t yet invaded nearby tissue. This is sometimes called “stage 0” cancer.

Colon polyps, for example, are often precancerous. Even though it can take 10 or more years to develop into cancer, they’re usually removed as a precaution.

Malignant tumors are cancerous.

Our bodies constantly produce new cells to replace old ones. Sometimes, DNA gets damaged in the process, so new cells develop abnormally. Instead of dying off, they continue to multiply faster than the immune system can handle, forming a tumor.

Cancer cells can break away from tumors and travel through the bloodstream or lymphatic system to other parts of the body.

Types of malignant tumors include the following:


The most common cancers are carcinomas, which develop in epithelial cells. They include the following:

  • Adenocarcinoma forms in cells that produce fluids and mucus. This includes many breast, colon, and prostate cancers.
  • Basal cell carcinoma starts in the lowest layer of the epidermis.
  • Squamous cell carcinoma forms in cells just beneath the outer surface of the skin, as well as organs like the bladder, intestines, kidneys, or stomach.
  • Transitional cell carcinoma develops in tissue called the epithelium or urothelium. Bladder, kidney, and ureter cancers may be this type.


Sarcomas begin in bones, soft tissues, and fibrous tissues. This can include:

  • tendons
  • ligaments
  • fat
  • muscle
  • blood and lymph vessels

Germ cell

Germ cell tumors begin in cells that produce eggs or sperm. They’re likely to be found in the ovaries or testicles. They can also develop in the abdomen, chest, or brain.


Blastomas start in embryonic tissue and developing cells in the brain, eyes, or nervous stem. Children are more likely than adults to develop blastomas.

Benign tumorsMalignant tumors
Don’t invade nearby tissue Able to invade nearby tissue
Can’t spread to other parts of the body Can shed cells that travel through the blood or lymphatic system to other parts of the body to form new tumors
Normally don’t return after they’re removedCan return after being removed
Usually have a smooth, regular shapeMay have an uneven shape
Often move around if you push on themDon’t move around when you push on them
Typically not life-threateningCan be life-threatening
May or may not need treatmentRequire treatment

If you discover a new or unusual lump on your body, see your doctor as soon as possible.

Sometimes, though, you may not know you have a tumor. It may be found during a routine screening or checkup, or during a test for some other symptom.

After a physical exam, your doctor may use one or more imaging tests to help confirm a diagnosis, such as:

Blood tests are another common way to help with diagnosis. But a biopsy is the only way to confirm the presence of cancer.

A biopsy involves removing a tissue sample. The location of the tumor will determine whether you need a needle biopsy or some other method, such as colonoscopy or surgery.

The tissue will be sent to a lab and examined under a microscope. Your doctor will receive a pathology report. This report will tell your doctor whether the tissue that was removed is benign, precancerous, or malignant.

Treatment for cancerous tumors depends on many factors, such as where the primary tumor is located and whether it’s spread. A pathology report can reveal specific information about the tumor to help guide treatment, which may include:

Genetics plays a role, so you can’t prevent all tumors. Still, there are steps you can take to lower your risk for developing cancerous tumors:

  • Don’t use tobacco, and avoid exposure to secondhand smoke.
  • Limit your alcohol consumption to not more than one drink per day for women, two drinks per day for men.
  • Maintain a healthy weight.
  • Include plenty of fruits, vegetables, whole grains, and beans in your diet while limiting processed meats.
  • Exercise regularly.
  • Protect your skin from the sun.
  • Get regular medical checkups and screenings, and report any new symptoms.

A tumor is a mass of abnormal cells. Many types of benign tumors are harmless and can be left alone. Others can cause serious problems or become cancerous.

Malignant tumors can be life-threatening. Benign or malignant, treatment depends on the specifics of the tumor.

If you feel a new lump anywhere on your body, see your doctor as soon as you can. Early diagnosis gives you more treatment options and a potentially better outcome.