Attention, all recruits, and commit these to memory. These are the four tenets of the Cancer Police:
- Detect and fight off invaders
- Recognise the body you serve, and protect it from attack
- Do not forgive or forget: remember previous offenders
- Exercise force with restraint—maintain homeostasis by suppressing your response once the threat is neutralised, preventing collateral damage to the body.
Cancer is the most insidious of organised crime networks that threatens to ruin our city. In taking this oath, you are promising to patrol the trillions of cells that are the building blocks of this body, and to identify and neutralise threats before they take root. Do not underestimate cancer, for it is a cunning master of disguise with a constantly evolving strategy. Cancer has no qualms: it bribes guards, recruits locals, and rewrites the city’s laws to suit its needs. But even the most sophisticated crime syndicate relies on its environment, and by unravelling the cancer ecosystem and the ‘exposome’—the cumulative measure of environmental influences that shape our health—we can learn how to support our immune system, our cancer police force, in defeating it. Here’s the latest intel.
Every breath you take
For decades, we have known that smoking causes lung cancer (among other types) primarily by directly damaging DNA in our cells. However, the realisation that air pollution threatens the peace of our internal cities even in non-smokers is a more recent one, with the WHO only classifying it as a Group 1 carcinogen (alongside smoking) in 2013. Since then, there has been an abundance of research that has pieced together how.
In 2022, the TRACERx Lung Cancer study revealed a mechanistic link in humans for the first time: chronic exposure to PM2.5 (air pollutants ≤2.5 microns in diameter) inflames lung tissue, essentially triggering a state of constant civil unrest. This is the signal for the syndicate’s ‘sleeper cells’—cells with cancer-causing mutations that would have otherwise been dormant and harmless—to wake up and proliferate. Our cancer police, distracted by the fires of inflammation, might then fail to spot the coup until it’s too late. Worse yet, the Sherlock-Lung Study (2025) implicated PM2.5 in DNA damage, associating high air pollution exposure with an increased prevalence of mutations to TP53 (the ‘guardian of the genome’). In effect, not only does air pollution awaken the ‘sleeper cells’, it dismantles the infrastructure of the city too.
Every move you make
Movement is medicine, and new research has proven its effectiveness in cancer. In 2025, the CO.21-CHALLENGE trial (the first Phase III, randomised control trial of its kind) found that cancer patients who underwent a three-year structured exercise programme after completing adjuvant chemotherapy remained disease-free significantly longer than those who were provided health education materials.
How does exercise achieve a 28% reduction in relative risk of recurrence, new primary cancer, or death? One explanation is that exercise triggers the release of adrenaline and myokines, blaring sirens that cause the release of immune cells, like natural killer and T cells, into the bloodstream; movement is a mobilisation order for our cancer police’s patrols. Moreover, exercise changes the terrain of the battlefield: tumours often defend themselves by creating a hostile, acidic (lactate-rich) microenvironment that exhausts immune cells; aerobic activity helps clear it. With more patrols, and a clearer field of view, any delinquent cells are more likely to be caught before they can cause any more damage to the body.
Every bond you break
Our internal city maintains a mutually beneficial treaty with the trillions of bacteria residing in our gut. In exchange for food and shelter, these microbial ‘informants’ teach our recruits how to distinguish between harmless tourists and dangerous infiltrators.
Unfortunately, the use of antibiotics can inadvertently break this bond at the worst possible moment. Whilst antibiotics are crucial lifesaving drugs, they are also blunt instruments that wipe out our microbial allies alongside invaders. The severing of this ancient bond is not without consequence. A 2019 study showed that patients who required antibiotics within 30 days of starting immune checkpoint inhibitors (ICI) saw significantly worse overall survival. Why? By taking out our friendly neighbourhood informants, antibiotics effectively cause a communication blackout just as the warrant (ICI) is executed. The cancer police are authorised to attack, but don’t know where to go. The proof of this came in 2021, when studies found that repairing the broken bonds (via faecal microbiota transplantation) could reverse resistance to the drugs. This confirms that the immune system does not function in isolation; to effectively fight cancer, we must protect the biological partnerships that underpin our existence.
Every step you take, your immune system’s watching you
Every single day, the cells in our bodies are accumulating mutations that could result in defection. Meanwhile, our diligent cancer police forces are constantly monitoring and responding to the threats that arise. As the commissioners of these sprawling internal metropolises, we have the power to make decisions that help to protect them. Personally, I am inspired by the fact that modern science has developed to the point that we can understand the mechanisms for how the most mundane of actions impact our most minute of pieces, and proud that I can contribute to it. I am comforted that we have agency: by clearing the air, mobilising forces, and repairing our alliances, we can ensure that for every step a cancer cell takes, the immune system is watching.
This piece was a runner up in the 2025 Mel Greaves Science Writing Prize
Ashley Wong is a PhD student in the Genomics and Evolutionary Dynamics lab. Her PhD focusses on the mechanisms of colorectal cancer metastasis. Prior to joining the ICR, she completed an MBiochem in Biochemistry at the University of Oxford.