The Big C’s: Climate Change and Cancer

"Disruptors" is a series sharing new and innovative ideas and viewpoints from Columbia Cancer researchers and clinicians.

For decades, researchers have known that climate change can cause cancer. In the 1940s, scientists discovered that heat is required for the activation of ultraviolet (UV) radiations’ tumor-forming ability; in the absence of heat, UV radiation did not promote tumor growth in mice. Recently, it was discovered that heat also worsens the effect of humidity on the human body, changing the expression of genes associated with oxidative stress, DNA repair and inflammation—drivers of cancer development. This is a result of epigenetic modification, one way the body responds to outside influences.

When it comes to fighting or slowing climate change, there has been a lot of emphasis placed on mitigating efforts, including changes in human behavior and the reduction of fossil fuel and electric power use. While it takes time, certain efforts to mitigate climate change have proven successful. 

But mitigation isn’t enough. What we’re finding is that adaptation is just as crucial. 

The question remains: Are we running out of time to manage climate change before it results in increased cancer rates and deaths in the United States? Perhaps we are not solely at the mercy of the environment we live in—our own bodies could have the capability to compensate for climate change.

How Our Epigenome Helps Us Adapt

Epigenetics is the biological ability to alter the expression of our DNA in response to environmental factors. Epigenetic modifications act on the epigenome, which is superficial to the genome. In this way our DNA remains unchanged, but the way in which its genes are expressed is changed. 

While our genome, which is comprised of DNA, is the body’s instruction manual, our epigenome is a network of structures surrounding DNA that control gene expression. DNA methylation or histone modifications are types of epigenetic reprogramming that alter the chromatin structure to turn the expression of a gene on or off, like a switch.

Simply put, if the DNA is the music notes telling genes how to express themselves, the epigenome serves as marks outlined in margins of sheet music, instructing musicians to play softer, louder or not at all.  

Epigenetic modification is an adaptive response to the environment that is designed to ensure the survival of the individual and eventually the species.

There is a lot that we can do to adapt to climate variation. But there is already this built-in system that we have in ourselves. The epigenome is meant to help us cope when things change around us or when we change environments.

Built-in Climate Change Resilience

The very trees and plants around us that serve as natural sinks, sequestering greenhouse gases from the atmosphere, undergo this natural epigenetic modification process. When plants are exposed to drought, cold, or salt water, they reprogram their epigenome, altering the expression of genes involved in growth and development. These changes allow the tree or plant to withstand harsh climate conditions that ordinarily would keep it from flourishing. These alterations are recorded for the future, allowing the plant to gain resilience to its new surroundings, and because epigenetic modifications are also heritable, subsequent generations are ensured through enhanced expression of genes controlling seed production.

Other species have been able to biologically adjust to the new environment created by climate change. These include a type of fish known as Winter Skate, which epigenetically modify themselves to become smaller in order to survive in poorly oxygenated water, as a result of rising sea temperatures.

Epigenetic modifications are not always beneficial and rising temperatures associated with climate change may have harmful consequences. In humans, DNA methylation of CRAT, a gene involved in growth and in development, is accelerated in cancer patients, and CRAT hypermethylation was also identified in people exposed to just three weeks of heat.

The good news is that epigenetic adaptations to heat could be temporary.

The evidence for that includes one species of guinea pig which, when studied, showed epigenetic adaptions to heat that were only retained and passed on to offspring produced during the time of exposure. Interestingly, once heat abated, the changes reversed, making the guinea pig able to adapt to both cold and warm climates. This is a perfect illustration of how epigenetic modification might function in humans: as a compensatory mechanism in which our gene expression can naturally fluctuate or be conditioned through therapeutic epigenetic reprogramming, to reduce the risk of cancer posed by climate change.

The Promise of Future Interventions

We know that climate change can lead to cancer, but through epigenetic modification, the human body might be adapted to the effects of rising temperatures and other environmental pressures. Researchers, including our lab, are investigating whether one day precision medicine could be used to tailor therapeutics or interventions that could induce favorable epigenetic changes for individuals to withstand climate change or reduce the potential of heat to cause cancer. 

For instance, imagine a future when, in spring, you could take a simple blood test to determine whether your body is ready to respond to the heat waves that you will experience in the summer. Your health care provider would then offer tailored plans for you to prepare for the summer. This is critical because while climate change is global, epigenetic research tells us that each of us has different exposures and unique responses. 

While we wait, and hope, that mitigating efforts resolve climate change, our bodies as well as science and medicine are adapting ways to cope with rising temperatures. We may soon find that we won’t need to look past ourselves for the key to surviving the effects of climate.

Andrea Baccarelli is the Leon Hess Professor and chair of environmental health sciences at Columbia University’s Mailman School of Public Health and a member of the Herbert Irving Comprehensive Cancer Center.

Stacia M. Nicholson is a postdoctoral research fellow in the Baccarelli Lab, where she examines air pollution and lead exposure in the development and progression of Alzheimer’s disease and age-related cognitive disorders.