Can Exercise Help Slow Breast Cancer Progression?

In recent years, there has been growing interest in how lifestyle factors influence cancer progression. Among these, physical activity has emerged as a powerful tool with the potential to impact tumor development.

Dr. Mhairi Morris, a researcher specializing in cancer biology at Loughborough University, has been investigating how exercise interacts with breast cancer at a molecular level. Her research seeks to answer a key question: Can exercise help slow or even prevent breast cancer progression?

Morris recently spoke to Technology Networks about how her lab is trying to answer this.

The biology of breast cancer and exercise

Breast cancer develops when cells in the breast tissue begin to grow uncontrollably, forming a malignant tumor. This growth is often driven by hormones, genetic mutations and environmental factors. One of the key players in breast cancer development is estrogen, a hormone that can fuel tumor growth. Factors like chronic inflammation and metabolic dysregulation also contribute to the progression of the disease.

Exercise has been shown to counteract these biological processes through four main mechanisms.

Lowering estrogen levels

"When women hit menopause, we stop producing estrogen from our ovaries. Fat cells are another source of estrogen, which is why women often find it really hard to lose weight when they hit menopause because their bodies are just clinging on to it," said Morris.

Since adipose tissue produces estrogen, higher body fat levels can increase estrogen exposure, promoting tumor growth. Normally, progesterone acts as a counterbalance to estrogen, functioning like a brake on its pro-growth effects. However, in obesity, while estrogen levels rise due to increased adipose tissue, progesterone levels do not increase proportionally. This leaves estrogen’s tumor-promoting effects unchecked. Physical activity helps counteract this imbalance by reducing adiposity, which in turn lowers estrogen production and decreases circulating estrogen levels in the bloodstream – creating a less favorable environment for cancer development.

Regulating metabolic markers

“It [exercise] also impacts your metabolic markers, things like insulin and insulin-like growth factor (IGF) receptor, which are key in driving cancer cell growth,” said Morris.

Elevated insulin and IGF levels have been linked to cancer cell proliferation, as they act as growth signals that encourage tumors to expand. Regular physical activity improves insulin sensitivity and reduces circulating insulin levels, potentially slowing cancer growth.

Reducing chronic inflammation

“People who are overweight or obese have chronic low-grade inflammation, which fosters that tumor growth, and exercise counteracts that,” said Morris.

Physical activity reduces pro-inflammatory cytokines and increases anti-inflammatory responses.

Mobilizing immune cells

Another way exercise can impact tumor growth is by enhancing the body's natural immune defenses, particularly through natural killer (NK) cell activation. These immune cells play a critical role in the body’s immune system, acting as first responders against abnormal or infected cells, including cancer cells. Unlike other immune cells that require prior exposure to a pathogen or cancerous cell, NK cells can identify and destroy malignant cells on contact. They do this by recognizing stress signals on the surface of tumor cells and releasing toxic molecules that trigger cell death.

One way exercise supports this immune response is through the release of adrenaline.

“Exercise mobilizes them [NK cells] because of the release of adrenaline when you do a bout of exercise that binds the receptors on the surface of these cells in the blood,” said Morris.

This surge of adrenaline temporarily increases the number of NK cells circulating in the bloodstream, enhancing the body’s ability to detect and eliminate cancerous cells.

“We also know from the literature that patients who undergo exercise before and during their chemotherapy regime tend to have a better response to chemotherapy,” Morris said in a talk she gave at the recent WORD+ 2025 conference.

Animal studies reveal the power of exercise

Morris and her team conducted a systematic review on the role of exercise in modulating breast cancer progression in vitro. They discovered various exercise interventions on breast cancer cells in vitro significantly reduced breast cancer cell viability, proliferation and tumorigenic potential.

“When we exercise, our body releases all manner of different components into the bloodstream – cytokines, chemokines, catecholamines, you name it. We call these exerkines, and these reduce tumor growth,” said Morris.

A Danish study on tumor-bearing mice demonstrated the power of this effect. Mice with access to a running wheel showed a >60% reduction in tumor incidence and growth across 5 different tumor models compared to sedentary mice. The researchers found that exercise increased the presence of NK cells in tumors.

Morris did, however, note that while exercise is beneficial in reducing the likelihood of developing cancer, its ability to shrink existing tumors was limited: “Sadly, it didn't appear to reduce the size of existing tumors. And this is the same in mice and humans. Because wouldn't that be amazing, being able to say to patients, you no longer have to take this horrendous therapy that makes you feel dreadful – you can just go and hop on a treadmill? Sadly, it’s not that simple.”

Despite these limitations, exercise’s ability to prime the immune system, particularly by activating NK cells, is a promising area of research. While it may not replace traditional cancer therapies, it offers a complementary approach that could improve outcomes and enhance the body’s natural ability to fight disease.

What type of exercise works best?

While the benefits of exercise for cancer patients are widely recognized, the optimal intensity and duration of exercise remain uncertain.

“The literature is a bit split, and nobody really knows the best type, how long to do it for or what intensity to do it for,” Morris explains.

While some studies suggest that higher-intensity exercise may offer additional benefits, findings in human and animal studies have been inconsistent.

“We know that six weeks of moderate-intensity exercise is sufficient to reverse the effects of, say, prediabetes, for example,” she added.

While some animal studies suggest that intense exercise may enhance immune responses, human studies have not always produced the same results.

“I was quite surprised that I didn't see much of a response in the model of moderate intensity exercise, because all the literature shows that it does,” Morris said in reference to an unpublished study from her lab.

The study involved a group of fit young individuals who completed a single bout of moderate- or high-intensity exercise. Post exercise, the participant’s blood was collected and the serum extracted from the samples was used to supplement their cell culture medium.

“This was a group of pretty much fit young people who had done one acute bout of exercise. And I do wonder how real those results were.”

This discrepancy highlights the need for further research, particularly in older adults and individuals at different cancer stages.

Importantly, even low-intensity exercise can have a meaningful impact.

“If you're really obese and you can't do high-intensity exercise, just walking and doing that regularly is good to lower those levels of inflammation.”

“I don't think we need to do high-intensity exercise, and actually, even physical activity – things like doing the housework, gardening – that all counts as activity. The overall suggestion is, ‘Sit less and move more’,” she said.

This is particularly relevant for cancer patients who may experience fatigue or other limitations due to treatment.

Could exercise be a standard part of cancer treatment?

As research continues to highlight the benefits of exercise for cancer patients, there is growing interest in integrating structured physical activity into standard cancer care. Some oncology programs are already incorporating exercise prescriptions, tailoring physical activity recommendations to individual patients based on their cancer type, treatment regimen and overall health.

“In America, there's a person who's developed an app where you can plug in your symptoms, your type of cancer and things that you're struggling with, such as what kind of symptoms and side effects you've got from your treatment. Then it'll spit out an exercise prescription for you,” said Morris.

Ultimately, exercise recommendations must be individualized.

“How I respond to exercise will be different from how you do, and if a patient’s got cancer, they’ve got a whole other set of challenges overlaid on top of that,” Morris said.

As researchers like Dr. Morris continue to explore these connections, the hope is that exercise will not only be recognized as a valuable supportive therapy but also integrated as a routine part of cancer treatment, improving outcomes and quality of life for patients.