Benign vs. Malignant: What's the Difference?

This page is for anyone who has seen the words benign or malignant on a scan or pathology report. It explains what each word means, how doctors tell them apart, and what a result does and does not tell you.

These two words come up early in almost every cancer work-up. Benign means not cancer. Malignant means cancer. What separates them is one specific ability: the ability to invade nearby tissue and spread to other parts of the body.

A benign growth is not cancer. NCI says benign tumors do not invade nearby tissue or spread to other parts of the body. When removed, they usually do not grow back.

Benign does not always mean "leave it alone," though. NCI notes benign tumors can sometimes be quite large, and can cause serious symptoms or even be life threatening, such as in the brain. Some are removed for that reason alone.

A malignant growth is cancer. It can grow directly into nearby tissue. It can also spread to distant parts of the body through the blood or the lymph system, a process called metastasis. This ability to invade and spread is what makes malignant growths dangerous, and it is the main reason they are treated.

NCI says the pathology report provides the definitive cancer diagnosis. A biopsy is a procedure to remove cells or tissue for a pathologist to examine. A pathologist, a doctor who specializes in diagnosing disease from tissue samples, writes up the findings in a pathology report.

That report typically states the diagnosis in plain terms: benign or malignant. If malignant, it usually also reports the grade. Grade means how abnormal the cells look, which relates to how the cancer is likely to behave. For a tumor that has been surgically removed, it also reports the margins: whether cancer cells reach the cut edge of the removed tissue. A "clean" or "negative" margin means no cancer cells were seen at the edge. A "positive" margin means some may remain.

A benign result rules out cancer in the sample taken, but it does not always end the conversation. If a growth is large, growing, or in an unusual location, your doctor may still recommend removing it or watching it, even without a cancer diagnosis.

A malignant result confirms cancer, but by itself it does not tell you the stage, whether it has spread, or what your specific outlook is. Those answers come from more tests, such as imaging, sometimes further biopsies, and blood work, combined with the original pathology report. A single word on a report is a starting point for a conversation, not the whole picture.

Waiting for a biopsy result is genuinely hard, but most biopsies are not emergencies in the sense of needing same-day answers. What matters more is following up. Know when your results will be ready. Have a plan for the appointment where they are discussed, rather than getting the news by an isolated phone call or portal message.

• Do you expect this growth to be benign or malignant, and how confident are you before the biopsy?
• Is a biopsy needed to know for certain, and what kind makes sense for this location?
• Once results are in: if it is malignant, what are the grade and margins?
• What happens next either way?

• NCI — What Is Cancer?
• NCI — Surgical Pathology Reports Fact Sheet