Experts have long suspected inflammation may play some role in cancer’s development. In 1863, German scientist and physician Rudolf Virchow was the first to make the connection, observing that cancer often develops at sites of chronic inflammation. But researchers have only recently pinpointed chronic inflammation as a primary risk factor for cancer and other serious health conditions. Among the reasons it’s taken science so long to confirm the relationship: Chronic inflammation causes few, if any, outward symptoms. And inflammation by itself is a sign the body is doing its job.
The concept of inflammation is sometimes tricky to grasp because it may seem contradictory. On one hand, inflammation is a healthy process, essential to the body’s ability to heal itself. When you have an infection or injury, the immune system releases white blood cells and chemicals to fight off the infection or repair damaged tissue. But when inflammation persists, or when the immune system triggers an inflammatory response when you don’t have an infection or injury—like that caused by arthritis and other autoimmune diseases—it may damage healthy tissues.
“Chronic inflammation is sometimes called ‘smoldering inflammation’ because it’s inflammation that never really resolves. It’s the opposite of ‘good’ inflammation, which your body uses to get rid of bacteria and viruses, and then, once it achieves its goal, resolves,”says Eugene Ahn, MD, Medical Director of Clinical Research and Hematologist/Oncologist at Cancer Treatment Centers of America® (CTCA), Chicago.
Today, researchers have a fairly broad understanding of inflammation’s split personality. They’ve learned that sometimes, chronic inflammation is caused by factors outside of our control, such as inherited gene mutations that raise the risk of chronic inflammation. But it also may result from lifestyle choices you may be able to change. That’s important because so-called lifestyle-dependent inflammation is on the rise. “The connection between inflammation and cancer has been apparent for a long time, but it may be that it’s now coming into sharper focus because of the increase in lifestyle-dependent inflammation we’re seeing,” Dr. Ahn says.
Chronic inflammation’s role in cancer development isn’t a small one. As many as one in five cancers are believed to be caused or influenced by inflammation. One reason is that chronic inflammation may damage DNA, says Cynthia Lynch, MD, Medical Director of the Breast Center and Medical Oncologist at our hospital near Phoenix. Other times, the inflammatory process produces molecules called cytokines, which stimulate the growth of blood vessels that bring oxygen and nutrients to the tumor. The process also may generate molecules called free radicals that further damage the DNA. These inflammation side effects may help sustain and fuel cancer growth.
The reason inflammation becomes chronic isn’t always apparent. It may be caused by infections that don’t go away, abnormal immune reactions to normal tissues, or certain conditions like obesity. Over time, chronic inflammation may damage DNA, leading to conditions like heart disease, type 2 diabetes, stroke and cancer. “Anything that causes inflammation will cause the DNA of a cell to replicate faster,” says Brad Mons, DO, Head and Neck Surgeon. “The more your cells replicate, the higher chance you have of cancers developing.”
Sometimes, cancer-causing chronic inflammation stems from a disease characterized by inflammation. The inflammatory diseases colitis, pancreatitis and hepatitis, for example, are linked to a greater risk of colon, pancreatic and liver cancers, respectively. In these diseases, immune cells create highly reactive molecules containing oxygen and nitrogen that can damage DNA. Inflammation also may cause cells to divide.
Chronic inflammation also may result from a chronic infection, like H. pylori, which is linked to stomach cancer, and hepatitis B and hepatitis C, which are linked to liver cancer. HIV increases the risk of other viruses and very rare cancers, including Kaposi sarcoma, non-Hodgkin lymphoma and invasive cervical cancer.
In other cases, environmental factors are the culprits. Asbestos exposure, for example, increases the risk for mesothelioma. Many environmental carcinogens and risk factors, in fact, are associated with some form of chronic inflammation. According to the National Institutes of Health, up to 20 percent of cancers are linked to chronic infections, 30 percent are linked to tobacco smoking and inhaled pollutants, such as asbestos, and 35 percent are linked to dietary factors, including obesity. “Whether it’s an autoimmune disease like lupus or rheumatoid arthritis, or irritations from a chemical you may be exposed to, such as asbestos, if we can reduce the amount of inflammatory processes in our environment, we can reduce our risk of cancer,” Dr. Mons says.
Ways to reduce the risk
Today, researchers are exploring whether oxygen sensors in the body can be manipulated to reduce chronic inflammation. One study found that tricking immune cells into believing they’re lacking oxygen makes them retreat from the site of inflammation to conserve energy. Researchers are now studying whether medications could be developed to turn on certain proteins that, when activated, inhibit the body’s inflammatory response.
Evidence is also building that aspirin may help prevent chronic inflammation. The non-steroidal anti-inflammatory drug works by reducing the production of prostaglandins, which are chemicals that promote inflammation, pain and fever. In a 2016 report published in the Journal of the American Medical Association, researchers who studied aspirin use in 135,000 patients concluded “long-term aspirin use was associated with a modest but significantly reduced risk for overall cancer, especially gastrointestinal tract tumors. Regular aspirin use may prevent a substantial proportion of colorectal cancers.” Already in the United States, tens of millions of adults take aspirin to reduce the risk of heart attack or stroke. “We take aspirin to prevent heart attacks, so taking it to prevent certain types of cancer isn’t unreasonable,” Dr. Ahn says.
The U.S. Preventive Services Task Force now recommends certain adults ages 50 to 59 years old take low-dose aspirin to help prevent colorectal cancer and suggests older adults also consider an aspirin regimen. “Aspirin is being looked at to treat other cancer types, as well, but there isn’t much data on anything other than colorectal cancer right now,” Dr. Lynch says.
With 35 percent of cancers linked to dietary factors like obesity, stress and lack of exercise, the association between lifestyle habits and inflammation remains a concern. These factors trigger an immune response, even without an infection to fight off or an injured tissue to heal. “The reason inflammation gets so much attention in the press right now is because a lot of it is dependent on our lifestyle,” Dr. Ahn says. “The more sedentary you are and the worse your diet is, the more inflammation you’re generating.”
In fact, a 2016 report from the American Institute for Cancer Research found that maintaining a healthy weight may be as important as avoiding tobacco and overexposure from the sun. And the American Cancer Society found that those who follow a healthy lifestyle, by eating a nutritious diet, limiting alcohol consumption and taking other important steps, are 10 to 20 percent less likely to be diagnosed with cancer.
Diet and exercise top the healthy lifestyle list, Dr. Lynch says. And even small changes can make a difference, like adding more plant-based foods that contain anti-inflammatory phytonutrients to your plate, and eating more fermented foods, such as yogurt and miso, which contain natural probiotics that reduce inflammation. Also, try to avoid carcinogens like asbestos, silica and tobacco, and, if you have an underlying condition like hepatitis B or hepatitis C, seek treatment.
Experts also recommend limiting processed foods, which may increase the risk of throat cancer. “It’s not significant, but the risk is more than it is for someone who eats fresh produce, because those preservatives are acting as irritants,” Dr. Mons says. Alcohol can act as an irritant, too, especially in the head and neck—the first area food or drink touches when swallowed. Another concern: Alcohol and its byproducts may damage the liver and lead to inflammation in the organ.
The bottom line: Focus on what you can change. “I always tell patients that there are certain things they have control over in their lives, and there are certain things they don’t, and they should only worry about the things they have control over,” Dr. Ahn says. “That’s where lifestyle comes into play.”