Could the air you breathe be silently raising your cancer risk? Fine particulate matter (PM2.5) and nitrogen dioxide (NO2), common in polluted air or smog, don’t just irritate the lungs; they can trigger changes in tissue stem cells, allowing pre-cancerous cells to grow long before a tumor is detectable.
Factors that trigger damage
The inhaled PM2.5 and NO2 molecules go into the body’s protective barriers and target the airway and skin stem cells. These pollutants cause severe oxidative stress by creating reactive oxygen species (ROS). The stress caused affects the cellular defenses and results in direct and indirect damage to the DNA. Stem cells have a long lifespan and regenerative capacity, but they are vulnerable to the accumulation of these mutations.
Ways of molecular transformation
Smog damage to DNA leads to oncogenic mutations in the tumor suppressor genes TP53 and KRAS. The constant inflammation due to pollution causes the damaged cells to become malignant. The activation of the aryl hydrocarbon receptor (AhR), a sensor that detects toxins like those in smog, causes metabolic disruption and drives chronic NF-kB inflammation. This long-term inflammation fuels pre-cancerous stem cells, helping them grow and survive.
Effects on stem cells
Chronic inflammation, oxidative stress, and activated AhR change the way stem cells behave. The mutated stem cells have enhanced survival rates and enable faster replication in comparison to healthy cells. The increased proliferation and pro-inflammatory atmosphere result in clonal expansion, which is the uncontrolled multiplication of a single and damaged cell lineage.
Tissues at high risk
Tissues that are highly exposed and have rapid cell turnover, like the lung bronchi and the skin’s basal layers, are most at risk. The effects are not always limited to these areas, as changes in circulating stem cells can have a broader, systemic impact on cancer risk.
Why does it matter?
Smog can increase the number of pre-cancerous stem cells, which raises the chance that one may develop into invasive cancer. For non-smokers in heavily polluted areas, this can mean earlier cancer development and a higher lifetime risk. Controlling air pollution is, therefore, an essential step in cancer prevention.