What is the role of chronic inflammation in the development of cancer?

Many cancers begin at sites where the body has been dealing with infection, irritation, or a chronic inflammatory disease over a prolonged period. Persistent inflammation promotes every step of tumour formation: from the initial DNA damage through to tumour growth and spread to other organs. This connection is strong and is broadly supported by research.

Around a tumour, a distinct micro-environment develops, populated by inflammatory and support cells. This environment acts as a breeding ground: it stimulates the formation of blood vessels so the tumour can obtain oxygen and nutrients, helps tumour cells escape the immune system, and makes the tumour more resistant to treatment. A key protein in this process is NF-kB, a kind of switch that controls inflammatory genes. When this switch is chronically turned on, it directly contributes to uncontrolled cell growth and metastasis, making it an interesting therapeutic target.

Not all inflammation is cancer-promoting, however. A short-lived, acute inflammatory response can actually activate immune cells that recognise and attack tumour cells. Chronic inflammation has the opposite effect: it exhausts the immune system and progressively trains it to tolerate tumour cells. A separate phenomenon in this context is the so-called tertiary lymphoid structures: small immune organs that can develop within tumours and actually strengthen the immune response. Their presence is associated with a better prognosis, although it has not yet been fully established whether they are the cause or the consequence.

Two specific lifestyle factors deserve attention. Fatty tissue in people with excess weight produces inflammatory substances that increase the risk of breast cancer and other cancers, and worsen prognosis. Notably, this also applies to people who are not classified as obese based on BMI but who do have inflamed fatty tissue. Chronically elevated insulin levels, such as those seen in obesity and type 2 diabetes, are likewise linked to inflammation and a higher cancer risk, although the causal relationship in humans has not yet been fully proven.