You probably know someone who caught lung cancer too late.
By the time a stubborn cough or a shortness of breath sent them to the doctor, the disease had often been quietly growing for years.
Scientists are now hunting for something that could sound the alarm much sooner.
A team at University College London says a shift in the body's own immune defenses may be that early warning.
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In the journal Nature, published on October 7, 2026, they describe an immune fog that appears months or years before a lung tumor shows up on any scan.
The fog is made of regulatory T cells, a type of white blood cell that normally stops the immune system from attacking the body itself.
In lung cancer, these cells appear to also shield pre-cancerous cells from being spotted and destroyed.
What the immune fog looks like
When the UCL team compared blood and lung tissue from people with early pre-cancerous airway changes against healthy samples, one subtype of regulatory T cell kept turning up before cancer appeared.
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It built up slowly over months, sometimes years. The team then designed a prototype blood test that picks up this signal. They are training AI tools on thousands of samples to tell apart people who went on to develop lung cancer from those who did not.
James Reading, an associate professor at UCL who co-led the research, told Cancer Research UK how a prototype blood test might work in practice.
"If we could measure that very early immune response in the blood, then that would give us an idea that somebody has an early and growing pre-cancer that we could intercept," Reading said.
Clearing the fog with existing drugs
The researchers also tested whether removing the fog could prevent cancer. In mice carrying pre-cancerous lung cells, a drug that blocks a specific immune pathway halved the share of animals that went on to develop lung cancer.
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None of the treated mice formed large tumors. The drug family already has human versions used against other cancers, which the team hopes could speed up clinical trials.
The findings are still at an early stage. Humans are not mice, and not every pre-cancerous lung lesion goes on to become cancer.
Anyone with a persistent cough, chest pain or breathing problems should see a doctor rather than wait for a test like this to arrive.
Why finding lung cancer early matters so much
Lung cancer is the leading cause of cancer death in the United States.
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The American Cancer Society expects about 229,410 new diagnoses and roughly 124,990 deaths in 2026.
Most of those deaths happen because the disease is caught late, when treatment options are far narrower. More Americans die from lung cancer each year than from colon, breast and prostate cancers combined.
The UCL team is now optimizing the blood test and plans to move toward the first human trials of a drug that could clear the fog before cancer forms.
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This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.