Few words are more dreaded to hear from a doctor than learning that a tumor has been discovered. It's something most people equate to significant illness, inconvenience, and even death. 

But what many people don't realize is that being diagnosed with a tumor and being diagnosed with cancer aren't necessarily the same thing; and having a benign tumor won't automatically upend your life. "In reality, any growth of cells qualifies as a tumor," says Dr. Ryan Osborne, a surgical oncologist and the director of the Osborne Head & Neck Institute in Los Angeles. From this perspective, "even an unusual pimple or a mole qualifies, which is why doctors sometimes recommend having them checked out," he says.

Indeed, the word "tumor” has a Latin root that simply means “swelling.” With these factors in mind, it can be helpful to know what a tumor is, what it's not, and when to worry. 

What is a tumor? 

The first thing to understand is that tumors start as clumps of cells "that begin to grow abnormally to form a mass," says Dr. Julie Gralow, the chief medical officer at the American Society of Clinical Oncology. 

This means tumors "are not mutants or Martians the way some people think they are," says Osborne. "They are cells that originate in our body every day, that, for whatever reason, have found a way to evade the normal life and death cycle of a cell." This enables this grouping of cells to continue to grow and multiply unregulated until they can cause problems.

Such tumors "can range from puny to massive - millimeters to literally inches or feet," says Dr. Scott Eggener, a urologic oncologist and the co-director of the UChicago Medicine High-Risk and Advanced Prostate Cancer Clinic. The largest tumor that's ever been recorded weighed 302 pounds. It was removed from a woman in 1991, who made a full recovery. 

Tumors can be benign, meaning they are not cancerous and only likely to grow where they are without spreading to other areas of the body. "Benign tumors are very common," Gralow says, "as most of us have lumps and bumps that we can see and feel that are not cancer." She says these types of tumors are usually not a problem, "but occasionally if they grow very large or start to compress blood vessels and nerves, they may need to be removed by surgery." 

On the other hand, malignant tumors are cancerous, and will usually spread throughout the body - often into critical organs and systems, which can make them life threatening. While malignant tumors are "less common than benign tumors, they are not uncommon," says Gralow. She says that current estimates show that 1 in 4 people in the U.S. will develop a cancerous tumor, "with risk increasing as we age." 

What causes tumors? 

The primary reason age is a contributing factor for tumor growth is because of declining immune health as we get older. "You're making tumor cells from the day you're born until the day you die," explains Osborne. "But the reason these cells don't actually grow into a tumor is because your immune system seeks out and destroys them before they have an opportunity to grow into a tumor." However, this seek-and-destroy element of our immune system declines (along with most other bodily symptoms) as we enter our 40s, 50s and beyond, "which is why tumors and cancers are more common later in life," he says. 

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Beyond aging, genetics can also play a part in the development of tumors. “Many tumors form spontaneously from mistakes or mutations that are made when our cells are dividing," explains Dr. Andrea Cercek, a gastrointestinal oncologist and co-director of the Center for Young Onset Colorectal and Gastrointestinal Cancers at Memorial Sloan Kettering Cancer Center. While this dividing is often thought to be random, "some of these mistakes or mutations arise from a hereditary predisposition," she says. 

Environmental risks are also a factor. Prolonged exposure to sunlight and ultraviolet radiation, for instance, has been shown to sometimes lead to melanoma - which is one type of tumor, usually referred to as skin cancer. "Smoking is another risk factor for developing many cancers including lung cancer and head and neck cancers," says Dr. Marissa Barbaro, a neuro-oncologist at the Perlmutter Cancer Center at NYU Langone Hospital—Long Island.

"Much of the time, however, we are not able to identify a clear cause for a tumor," she adds. 

Is there a way to prevent tumors?

While "tumors can never be avoided completely," says Osborne, there are ways in which risks can be diminished.

For one, maintaining a strong immune system is crucial. This can be helped through getting adequate sleep, exercising regularly, minimizing stress, eating a well-balanced diet with plenty of fruits and vegetables, and maintaining a healthy weight, he says.  

Avoiding risk factors associated with malignant tumor growth is also important. These include protecting your skin from sunlight exposure, limiting the amount of alcohol you drink, and avoiding tobacco, per the Centers for Disease Control and Prevention (CDC).

Staying up to date on cancer screenings and catching malignant or premalignant tumors early in their growth is also crucial. "Cancer screening means checking your body for cancer before you have symptoms," notes the CDC. "Getting screening tests regularly may find breast, cervical, and colorectal (colon) cancers early, when treatment is likely to work best."