What"s the Difference Between Benign and Malignant Tumors?

By Health & Medical Half year ago

Updated March 12, 2015.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

"Is it benign or is it malignant" (benign vs malignant?) is a question that haunts too many people as they wait for a doctor’s visit, or the results of a scan or biopsy. How are these two terms defined? How are they similar, and what are the differences between benign and malignant tumors?

Definitions of Benign vs Malignant

The term benign is used to describe both medical conditions and tumors, and usually refers to a process that's not especially dangerous.

For example, a benign increase in blood pressure would be an increase that's not dangerous, and a benign heart murmur (also called an innocent heart murmur) would be a heart murmur that probably causes very few problems in terms of sickness or the potential for death. A benign tumor or mass is one that may be a nuisance, but does not usually result in death. Uterine fibroids are a common benign tumor frequently found in women who are perimenopausal. Benign tumors grow locally but do not have the ability to spread to other regions of the body.

The term malignant is often used synonymously with the word “dangerous” in medicine. While it usually refers to a cancerous tumor, it may be used to describe other medical conditions. For example, malignant hypertension (malignant high blood pressure) refers to blood pressure that is dangerously high, and malignant tumors (cancerous tumors) are those that have the ability to spread to other regions of the body either locally, via the bloodstream, or through the lymphatic system.

How are Malignant and Benign Tumors Similar?

Some similarities include:

Both can grow quite large. Size alone does not make the distinction between these types of tumors. In fact, benign ovarian tumors weighing over a hundred pounds have been removed.
Both can be dangerous at times. While benign tumors tend to be more of a nuisance, they can, in some cases, be life threatening. An example is benign brain tumors. When these tumors grow in the enclosed space of the brain, they can put pressure on, and destroy other brain structures, resulting in paralysis, speech problems, seizures, and even death. Some benign tumors, such as pheochromocytomas, secrete hormones that can cause life-threatening symptoms as well.
Both can recur locally. If cells are left over after surgery, both benign and malignant tumors may later recur near the region of the original tumor.

Differences Between Benign and Malignant Tumors

Rate of growth - In general, malignant tumors grow much more rapidly than benign tumors, but there are exceptions. Some malignant (cancerous) tumors grow very slowly, while some benign tumors grow rapidly.
Ability to metastasize - Benign tumors expand locally, whereas malignant tumors can spread (metastasize) to other parts of the body by way of the bloodstream and lymphatic channels. Check this article to see how cancer spreads.
Site of recurrence - While benign tumors may recur locally — that is, near the site of the original tumor — malignant tumors may recur at distant sites, such as the the brain, lungs, bones and liver, depending on the type of cancer.
”Stickiness" - The cells in benign tumors manufacture chemicals (adhesion molecules) that cause them to stick together. Malignant tumor cells do not produce these molecules and can break off and “float away” to other regions of the body.
Tissue invasion - In general, malignant tumors tend to invade nearby tissues, whereas benign tumors do not (though they may grow large and cause damage to nearby organs by creating pressure on them). A very simplistic way of thinking about this is to envision a benign tumor as having a wall or boundary (literally, a fibrous sheath surrounding the tumor). This boundary allows the tumor to expand and push (displace) nearby tissues aside, but does not allow the tumor to penetrate nearby tissues. In contrast, envision cancer as having “fingers” or “tentacles” that can reach into nearby tissues. In fact, the Latin word cancer derives from the word crab, used to describe the crablike, or fingerlike, projections of cancerous tumors.
Cellular appearance - Under a microscope, cells that are benign often look much different from those that are malignant. One of these differences is that the cell nucleus of cancer cells is often larger and appears darker due to an abundance of DNA.
Effective treatments - Benign tumors can usually be removed with surgery alone, while cancerous (malignant) tumors will often require chemotherapy and radiation therapy. These additional treatments are needed to attempt to reach cancer cells that have spread beyond the region of the tumor or are left behind after surgery for a tumor.
Likelihood of recurrence - Benign tumors seldom recur after surgery, whereas malignant tumors recur much more commonly. Surgery to remove a malignant tumor is more difficult than surgery for a benign tumor. Using the fingerlike analogy above, it is much easier to remove a tumor that has a clear fibrous boundary than a tumor that has penetrated nearby tissues with these fingerlike projections. If cells are left over from these fingers, the tumor is more likely to come back.
Systemic effects - Malignant tumors are more likely to have systemic, or total body, effects than benign tumors. Due to the nature of these tumors, symptoms such as fatigue and weight loss are common. Several types of malignant tumors also secrete substances that cause effects on the body beyond those caused by the original tumor. An example of this is the paraneoplastic syndrome caused by some cancers, resulting in a wide array of physical symptoms from hypercalcemia (an elevation of calcium in the blood) to Cushing’s syndrome (which in turn causes symptoms such as rounding of the face, stretch marks and weakened bones).
Death toll - Benign tumors cause around 13,000 deaths per year in the United States. The number of deaths that can be blamed on malignant (cancerous) tumors is over 575,000.

Areas of Confusion

There are times when it's difficult to know whether a tumor is benign or malignant, and this can be very confusing and frightening if it is you that is living with one of these tumors. Physicians often make the distinction between cancerous and non-cancerous tumors under the microscope, and sometimes the differences are very subtle. Sometimes doctors have to use other clues, such as where the tumor is located, its rate of growth, and other findings, to try and make the distinction.

In addition, some benign tumors can become malignant tumors over time. Some benign tumors very rarely become malignant tumors, whereas other benign tumors frequently transform into malignant tumors. An example of this is adenomatous polpys (adenomas) in the colon. By themselves, these are benign and not dangerous. But over time, they may transform into a colon cancer. Removal of adenomas in order to reduce the risk of developing colon cancer (adenocarcinoma) is behind the recommendation that people over the age of 50 have a screening colonoscopy.

Another area of confusion is that frequently normal cells, precancerous cells, and cancerous cells all coexist within the same tumor. Depending on where a biopsy is done, it may not pick up a sample representing the whole tumor; for example, it may only pick up an area of precancerous cells in a tumor that is otherwise cancerous.

Other terms that can make this concept confusing include:

Tumor: A tumor refers to a growth that can be either benign or malignant. It is essentially a tissue growth that does not serve any useful purpose for the body, and may instead be harmful.
Mass: A mass can also be benign or malignant. In general the term mass is used to describe a growth that is greater than or equal to 3 cm (1 ½ inches) in diameter.
Nodule: A nodule may also be either benign or malignant. In general, the term nodule is used to describe growths that are less than or equal to 3 cm (1 ½ inches) in diameter.
Neoplasm: Literally translated as "new tissue," the term "neoplasm" is usually used synonymously with tumor, and these growths can be either benign or malignant.

Understanding Cancer Cells

_Sources:

_{American Cancer Society. The History of Cancer. Updated 06/12/14. http://www.cancer.org/cancer/cancerbasics/thehistoryofcancer/the-history-of-cancer-what-is-cancer}

_{Johns Hopkins Medicine. What are Tumors? Accessed 08/20/14. http://pathology.jhu.edu/pc/BasicTypes1.php}

_{National Cancer Institute. What is Cancer? Updated 03/07/14. http://www.cancer.gov/cancertopics/cancerlibrary/what-is-cancer}

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