Why Do We Get Cancer? How Our Lifestyles Impact Our Risk

There are many factors that dictate whether someone will develop cancer, and they fall roughly into two categories: genetic and environmental.

With respect to genetics, certain variants of some genes, like BRCA (breast cancer) genes, can predispose one to cancer and can be passed from parents to children.

On the other hand, we are exposed to environmental factors through our daily lives – both actively through our behaviors and passively based on where we live, the water we drink, and the air we breathe.

For decades, we have appreciated the role of lifestyle, and known that high-risk health behaviors such as smoking cigarettes, drinking alcohol, and sunbathing increase risks of lung, liver, and skin cancers, respectively.

Other behaviors, such as alcohol consumption and consuming unhealthy foods, can increase the risk of cancer diagnosis as well.

Smoking & Air Quality

The hard evidence that cigarette smoke is a carcinogen made waves in courtrooms, newsrooms, and broadly throughout society in the 1990s. Since then, our knowledge of the link between tobacco smoking and cancer has surged.

Cigarette smoking can cause several types of cancer, but none more so than lung cancer. CRI Scientific Advisory Council member Patrick Hwu, MD, with the Moffitt Cancer Center has stated that cigarette smoke is responsible for DNA mutations that can disguise lung cancer to look like a foreign body and a virus, complicating diagnosis and treatment.

There are also instances where air quality can contribute towards cancer. In these cases, environmental circumstances are the culprit and individuals’ behaviors don’t contribute towards contracting cancer.

Sunbathing

A staggering 90 percent of skin cancers are caused by exposure to the sun’s harsh, ultraviolet (UV) rays. These UV rays are an invisible form of radiation produced by the sun, tanning salons, and sunlamps.

Absorbing UV rays can damage skin cells and lead to contracting cancer on sun-soaked areas of the body, such as the face, head, and limbs.

While one in five Americans will be diagnosed with a form of skin cancer prior to reaching age 70, there is also good news: thanks largely to advances in immunotherapy, over 99 percent of skin cancer cases are successfully treated.

Alcohol Consumption

There’s a growing consensus that alcohol consumption, particularly in excess, can contribute toward a greater risk of getting cancer.

As of March 2023, the Center for Disease Control (CDC) has reported that several studies demonstrate three or more alcoholic drinks per day creates a greater risk of developing stomach and pancreatic cancers.

Alcohol consumption is also linked with other types of cancers, including head and neck, breast, esophageal, and liver.

CRI Lloyd J. Old STAR Gregory Sonnenberg, PhD, of Weill Cornell Medicine, says that it is common practice for your doctor to tell you that avoiding alcohol is one way to guard against cancer.

Furthermore, recent research establishes around 4% of cancers worldwide are caused by ingesting alcohol.

Dietary Impact on Cancers

The food we consume is another aspect of human lifestyles that can contribute to the development of cancer. When we think of our digestive system, many of us just consider the stomach and intestines.

While our dietary intake can contribute towards stomach cancer, it can also lead to melanoma, uterine, colorectal, ovarian, and prostate cancers. CRI Postdoctoral Fellow Rebecca Delconte, PhD, of Memorial Sloan Kettering Cancer Center, cites emerging scientific proof that dietary restriction can improve the elimination of cancer cells.

For example, the lab Dr. Delconte works in has demonstrated that a cyclic fasting diet in mice can bolster natural killer T (NKT) cell responses against tumors. The evidence shows that diets higher in vegetables, whole grains, and fruit, coupled with avoiding red meat, can help people to reduce the risk of cancer.

Avoiding excessive UV rays, drinking alcohol, and cigarette smoking can also decrease the risk of cancer. There is no silver bullet for avoiding cancer through our behaviors and diet, but doctors and scientists agree that we can directly impact our chances of contracting cancer through what we put on and in our bodies.

For example, we know that dietary fiber and probiotics positively impact the gut microbiome and immune response to melanoma. While further research is necessary to better understand these connections, the findings in this study demonstrate positive outcomes for patients who were given targeted probiotics and bacterial consortia.

This research was led by CRI Scientific Advisory Council member Jennifer Wargo, MD, of the University of Texas MD Anderson Cancer Center, and was also co-authored by CRI Postdoctoral Fellow Marie Vetizou, PhD, of the National Cancer Institute.

The Microbiome

Our microbiome consists of all the microscopic organisms that live in and on us. This includes viruses, fungi, and the bacteria that make their home on our skin and in our gastrointestinal tract, among other places.

Although the microbiome’s relevance didn’t receive mainstream medical appreciation until the 1990s, there has since been an outpouring of scientific research on its relationship with cancer.

According to Dr. Sonnenberg, a symbiotic relationship exists between the microbiome and the immune system, at least under healthy conditions. The microbiome primes and supports the immune system’s ability to protect us against harmful pathogens that infiltrate or are normally kept in check in our intestinal tract, where the immune system localizes to deal with constant influxes of bacteria and other microbes from the food we consume.

Our diets and behaviors can directly impact the microbiome, and therefore, the immune system and its response to cancer.

Obesity

According to CRI Postdoctoral Fellow Claire McIntyre, PhD, of Brigham & Women’s Hospital/Harvard Medical School, obesity is likely to surpass smoking as the foremost preventable cause of cancer.

However, a vast majority of the public is woefully unaware of this link, creating a need for improved, streamlined communication about the factors leading to obesity and how obesity can lead to cancer.

While using mouse models, Dr. McIntyre discovered that consuming animal fat both aids tumor growth and reduces the number of anti-tumor immune cells. She is currently probing the mechanism underlying consumption of animal fats towards magnified tumor growth.

Dr. McIntyre isn’t the only CRI Scientist focused on deepening our knowledge of how obesity fosters cancer development. CRI Lloyd J. Old STAR Alexander Marson, PhD, of the University of California, San Francisco, works with genome-editing tools to better recognize cancer cells and eliminate tumors. Dr. Marson and his research team cite recent evidence that points to obesity and metabolic diseases’ ability to negatively affect the immune system.

While the underlying mechanism is still unclear, what is known is that lean mice responded to treatment more positively than their obese counterparts.

Cause and Effect

While many genetic and environmental factors can contribute towards contracting cancer, the scientific and medical communities are always striving to better understand cause and effect.

This is an area of research that, while well-established, is fluid and evolving. The more we learn about these links, the better we’ll be positioned to fully realize a world immune to cancer.