What's the difference? Benign and malignant tumors

Not all tumors are malignant, or cancerous, and not all are aggressive.

There is no such thing as a good tumor. These masses of mutated and dysfunctional cells may cause pain and disfigurement, invade organs and, potentially, spread throughout the body. But not all tumors are malignant, or cancerous, and not all are aggressive. Benign tumors, while sometimes painful and potentially dangerous, do not pose the threat that malignant tumors do. "Malignant cells are more likely to metastasize [invade other organs]," says Fernando U. Garcia, MD, Pathologist at our hospital in Philadelphia. "They grow faster, and they are more likely to invade and destroy native organs."

Benign tumors don't generally invade. They usually push the normal tissue to the side.” - Fernando U. Garcia, MD, Pathologist

Malfunctioning DNA

Tumors grow because of a malfunction in cells' DNA, mainly in genes that regulate cells' ability to control their growth. Some damaged genes may also prevent bad cells from killing themselves to make room for new, healthy cells. "The regulation of cell death so important," Dr. Garcia says. "If your programmed cell death is altered, the cell does not knows when it's time to die and persists. If the cell learns how to block that, and it develops the ability to proliferate, tumors grow more rapidly." Some of these mutations lead to rapid, unchecked growth, producing tumors that may spread quickly and damage nearby organs and tissue. "Malignant cells have the ability to produce enzymes that dissolve the native tissue. This is known as invasiveness," Dr. Garcia says. Other mutations are less aggressive, forming slow-growing tumors that are not cancerous. "Benign tumors don't generally invade," Dr. Garcia says. "They usually push the normal tissue to the side."

Many people carry benign tumors their entire life. Nevi, or moles, are types of benign tumors that may never need treatment. Other types of benign tumors include:

  • Adenomas: These bumps form on the surfaces of G-I tract. "A colon polyp, a classic adenoma, has only a 1 percent chance of becoming cancer in the patient's lifetime," says Jeffrey Weber, MD, Gastroenterologist at our hospital near Phoenix.
  • Fibromas: These tumors of connective tissue may be found in any organ. Fibroid tumors are named for where they form in the body, such as uterine fibroids.
  • Desmoid tumor: These are often more aggressive than most benign tumors and may invade nearby tissue and organs. But they do not metastasize.
  • Hemangiomas: These tumors are a collection of blood vessel cells in the skin or internal organs. They may appear on the skin as a birthmark-like discoloration and often disappear on their own.
  • Lipomas: These soft, round, fatty tumors are often found on the neck or shoulders.
  • Leiomyomas: The most common gynecologic tumors in the United States, these may be found in the uterus. Their growth is fueled by hormones.

How do you know if a tumor is cancerous?

The only way to be certain if a tumor is benign or malignant is with a pathology examination. While benign tumors rarely become malignant, some adenomas and leiomyomas may develop into cancer and should be removed. Desmoid tumors and fibroids also may cause damage if they are allowed to grow and may require surgery or a polypectomy. But while benign tumors may require some treatment, the cells that form them share few of the characteristics of aggressive cancer cells, Dr. Garcia says. 

"Cancer is an evolution," he says, adding that benign tumors do not evolve in the same way. "A cancer cell learns how not to die. Then it learns how to proliferate. Then it learns how to invade. Then it learns to metastasize. Cells are the building blocks of cancer."

Still wondering, what exactly is cancer? Learn more.