The short answer
A tumor is a lump of extra cells. Benign tumors are not cancer and do not spread, while malignant tumors are cancer and can invade nearby tissue and spread to other parts of the body.
A tumor is an abnormal mass that forms when cells grow more than they should.
Benign tumors are not cancer; they do not spread to other parts of the body.
Malignant tumors are cancer; they can invade nearby tissue and spread.
Some benign tumors still need treatment if they press on organs or nerves.
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The full explanation.
The simple version
A tumor is simply a lump of extra cells. The important question is whether it is benign (not cancer) or malignant (cancer). That difference shapes what happens next.
Benign tumors
Benign tumors are not cancer. They tend to grow slowly, have clear borders, and — most importantly — do not spread to other parts of the body. Many are harmless and simply watched.
Benign tumors are not cancer and do not spread.
Malignant tumors
Malignant tumors are cancer. They can grow into nearby tissue and can spread to distant parts of the body through the blood or lymph system, a process called metastasis. This ability to invade and spread is what makes them dangerous.
Telling them apart
Doctors often cannot tell for certain by imaging alone. A biopsy — removing a small sample to examine the cells under a microscope — is usually how they confirm whether a tumor is benign or malignant. Some benign tumors are still removed if they press on organs or nerves.
Words to know
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Common questions
▸What is a tumor?
A tumor is a mass that forms when cells grow and divide more than they should, or do not die when they should. Not all tumors are cancer.
▸What is the difference between benign and malignant?
Benign tumors are not cancer and stay where they start; they do not spread. Malignant tumors are cancer and can grow into nearby tissue and spread to other parts of the body.
▸Are benign tumors harmless?
Often, but not always. A benign tumor can still cause problems if it grows large or presses on an organ, nerve, or blood vessel, and some are removed for that reason.
▸How do doctors tell them apart?
Doctors often use a biopsy — removing a small sample of the tumor to examine the cells — along with imaging, to tell whether a tumor is benign or malignant.
Questions to ask your doctor
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