Chronic Inflammation and Breast Cancer: Is There a Link?

Medically Reviewed by Brunilda Nazario, MD on January 15, 2021
5 min read

There's been a lot of research on a potential link between chronic inflammation and breast cancer. For example, some studies show that chronic inflammation may lead to a higher risk of breast cancer coming back (you’ll hear this called recurrence).

Other studies have shown that anti-inflammatory drugs called NSAIDs may reduce the risk of developing breast cancer. And there’s evidence that chronic inflammation may contribute to cancer spreading, and to resistance to cancer treatments too.

Here’s what we know about the relationship between chronic inflammation and breast cancer, as well as where the research is headed.

Inflammation is a normal response to infections or injury, says Cynthia Lynch, MD, a medical oncologist and breast cancer program clinical advisor at Cancer Treatment Centers of America in Phoenix, AZ.

But chronic inflammation can result from infection, obesity, a sedentary lifestyle, and things like alcohol or tobacco, she says. “Chronic inflammation can, through many mechanisms we are still trying to understand, support cancer development and survival of cancer cells.”

She also points out that chronic inflammation may not be as obvious as acute inflammation that results from infection or injury.

Though the topic of how inflammation may lead to an increased risk of developing cancer, including breast cancer, is popular these days, there are still a lot of questions surrounding this possible link.

“It’s really a challenging topic,” says Naoto Tada Ueno, MD, PhD, a breast cancer specialist at The University of Texas MD Anderson Cancer Center in Houston. “I think inflammation does contribute to developing cancer, not just breast cancer, but any cancer, as well as potentially making the cancer more likely to spread.”

What’s less clear, he adds, is whether controlling inflammation really plays a role in survival rates or preventing cancer from spreading. “That is a question mark,” he says.

Ueno specializes in inflammatory breast cancer, a rare form of the disease that he says represents around 2% to 4% of cases. But even with common forms of breast cancer, there’s a subset of people that have inflammation.

“People are trying to dissect exactly what the trigger is of this inflammation. If we could understand the mechanism and define this, then I think we could intervene and make a difference,” he says. “That’s where the science stands at this moment.”

Inflammation happens when your immune system responds to an injury to your tissues, like from bacteria, trauma, or toxins. Because of this, “one hypothesis is that (the link between inflammation and breast cancer) has to do with our immune response,” says Tina J. Hieken, MD, a cancer surgeon at the Mayo Clinic and professor of surgery at Mayo Clinic College of Medicine in Rochester, MN.

“One of the interesting observations that our group at Mayo Clinic made is the presence of immune cells right in the breast lobule,” Hieken says. “The thought was that there must have been some type of exposure to microbes in order for there to be immune cells in that area.”

This led to a study published in 2016 in which Hieken and her team found that breast tissue collected from sterile surgical samples of both women with benign (noncancerous) breast disease and women with invasive breast cancer had bacterial DNA present, even though the women didn’t have any infection. This showed that breast tissue has its own distinct microbiome -- a community of microbes, which consist of bacteria, viruses, fungi, and protozoa.

The researchers also found noticeable differences between the breast tissue microbiomes of women with breast cancer and women with benign disease. “That could be an explanation of this association with inflammation,” Hieken says. Why? Because research has shown that microbes influence inflammation.

We have trillions of microbes in and on our bodies, and most of them are in our gut. Hieken says there have been some interesting studies on the gut microbiomes of people who already have cancer. Research has found that people who have a good response to immunotherapy to treat their cancer seem to have a different microbiome than those who don’t respond as well.

Now scientists are looking at changing a person’s microbiome using fecal transplant. This procedure involves transferring stool from a donor into the host’s gastrointestinal tract, usually with a colonoscopy. “It’s a way of changing that bacterial environment,” Hieken says.

She points to a just-published phase I clinical trial in which 10 people with melanoma were treated with a fecal transplant. Three had a positive response to immunotherapy afterward, even though they hadn’t responded to the treatment before. It’s really exciting to see this move forward, Hieken says. “It may be one point of the connection between cancer risk and inflammation.”

This is important for people who already have breast cancer too, since research suggests that microbes, particularly ones in the gut, may play a role in breast cancer progression.

“If you ask me if there are particular drugs or a particular approach that’s definitely proven to make a big difference, the answer is no at this moment,” Ueno says. “I think something more exciting will come out down the road. Even 10 years ago, nobody was excited about immunotherapy in breast cancer and now there’s a dramatic shift in how we approach it. I think what’s going to happen over the next 10 years is that we’ll understand inflammation in more detail and what causes it so we know exactly what medical intervention we need to improve the outcome of breast cancer.”

In the meantime, since things like stress, obesity, being sedentary, and poor diet can play a role in inflammation, lifestyle changes can really help, Lynch says. Plus, Ueno adds, “general lifestyle modifications benefit not just inflammation, but other health conditions too.”

Here’s what all three experts recommend to reduce chronic inflammation:

  • Maintain a healthy weight. This is actually thought to be the No. 1 way to reduce chronic inflammation. Being overweight or obese can lead to insulin resistance, Ueno says, which can lead to uncontrolled blood sugar and inflammation.
  • Exercise regularly. Getting regular exercise is another inflammation buster, so aim for at least 30 minutes of moderate activity every day.
  • Limit alcohol intake. Any more than 1 drink per day for women and 2 per day for men can ramp up inflammation. Alcohol has also been linked to an increased risk of breast cancer, as well as other cancers.
  • Stop smoking. Research shows that cigarette smoking is linked to inflammation, so this is yet another good reason to ditch the cigarettes.
  • Make sure any chronic health conditions you have are well-controlled. When they’re uncontrolled, conditions like diabetes and autoimmune diseases increase your body’s state of inflammation. Treatment helps keep inflammation in check, so see your doctor regularly and take your medications as prescribed.
  • Learn to manage stress. Chronic stress can increase inflammation, so it’s important to have healthy ways to cope. Try yoga, meditation, taking a walk with a friend, journaling, or listening to music.