Benign vs. Malignant Tumors

This page is for anyone who has been told they have a growth or tumor and wants to understand the words benign and malignant. It explains the difference, how doctors tell them apart, and what comes next.

Not every lump is cancer. Doctors sort abnormal growths into two broad groups: benign and malignant. Benign means not cancer. Malignant means cancer. The difference is not about size. It is about how the cells behave.

A benign tumor stays where it started. It does not invade nearby tissue, and it does not spread to other parts of the body. Once removed, a benign tumor usually does not come back. That said, benign does not always mean harmless. NCI says benign tumors can sometimes be quite large, and some can cause serious symptoms or be life threatening, such as benign tumors in the brain.

A malignant tumor is cancer. Cancer cells grow in ways normal cells do not. They keep growing even without the signals that normally tell a cell to stop. They ignore the signals that would normally tell a damaged cell to die. Malignant cells can invade nearby tissue directly. They can also break away and travel through the blood or lymph system. Then they can start new tumors elsewhere in the body. This spread is called metastasis.

NCI says that in most cases doctors need to do a biopsy to be certain someone has cancer. Abnormal tissue is removed and a pathologist examines it under a microscope. Imaging tests like ultrasound, CT, or MRI help doctors find tumors, but NCI says no single test can diagnose cancer, so results are combined with biopsies and other tests.

Most cancers form a solid mass, called a solid tumor. But some cancers do not work that way. Leukemia is a cancer of the blood and bone marrow. Instead of forming a lump, abnormal white blood cells build up in the blood and marrow. These are still cancers, even without a solid tumor.

Whether a growth is benign or malignant changes what happens next. Ask your care team what your result means for you, and whether the tumor needs treatment or watching. A malignant tumor is staged, and the results guide a treatment plan.

Once a tumor is confirmed malignant, doctors describe it further using grade and stage. Grade describes how abnormal the cancer cells look under a microscope; NCI says the more normal they look, the more slowly the cancer grows and spreads. Stage describes how large the cancer is and how far it has spread. Doctors use these together with other factors to plan treatment.

Waiting for a biopsy result is one of the hardest parts of this process. Ask your doctor how long results usually take, and what the next steps look like either way. It is normal to prepare yourself for either outcome, and it is also normal to feel relief that is hard to put into words if the result comes back benign.

• Does my growth need a biopsy to be sure, or is imaging alone enough to tell?
• What does "benign" or "malignant" mean for my case, not just in general?
• If it is benign, does it need to be removed or just watched?
• If it is malignant, what happens next, and how soon?

• National Cancer Institute — What Is Cancer?