What's the Difference Between a Neoplasm and a Tumor?

Ronald Reagan Points to Neoplasm on Nose — President Ronald Reagan points to a bandage after having a basal cell neoplasm removed from his nose in 1987. A neoplasm is an abnormal proliferation of cells that begins to create a mass totally unlike the normal tissue around it. Diana Walker/Getty Images

Almost 2 million people will be diagnosed with cancer in the United States this year alone. That's pretty scary, but diagnosing cancer is complicated and there is lots of jargon associated with it.

Take, for instance, neoplasm and tumor. You have probably heard of one of these, but maybe not the other. The good news is, these things mean essentially the same thing, which cuts down on the amount of learning you have to do. However, although they're synonymous with each other, it's like saying one of them is a 6th grader and the other is a middle schooler: basically the same thing, but there can be exceptions.

The word "tumor" comes from the Latin word for "bulge" or "swell." For this reason, a tumor can be any type of swelling or mass of abnormal cells in the body. Even though cells in different parts of the body have very specialized jobs, one thing they all have in common is their habit of continually replicating themselves perfectly in order to assure the pancreas or the lung has fresh, properly functioning cells at the helm. But sometimes the cells start making new cells all wrong — maybe the DNA is messed up, but they keep replicating themselves imperfectly over and over, regardless. The resulting knot of cells is a tumor.

What is a Neoplasm?

A neoplasm is an abnormal proliferation of cells that begins to create a mass totally unlike the normal tissue around it. Neoplastic cells can be malignant, meaning the cells are cancerous: They replicate very quickly, attack surrounding tissue and can even enter the bloodstream, wreaking havoc on far-flung regions of the body — this is called metastatic cancer.

The neoplasm could also be benign, meaning it is not cancerous and doesn't pose much of a threat to the surrounding tissue (think of a mole on the skin or uterine fibroids), although the cells could eventually develop into cancerous cells.

A neoplasm and a tumor are almost always considered interchangeable terms, although neoplastic cells are generally not considered tumors in the case of leukemia — a cancer of the blood and bone marrow — and certain types of skin cancer.