Researchers who sampled the lungs of 100 patients at a Greek teaching hospital found tiny plastic fragments in the airways of most of them.
In the 50 patients with lung cancer, the plastics showed up more often, and in greater quantities, than in the 50 without the disease.
The team presented the findings at the European Respiratory Society Congress in Barcelona.
The study is small, unpublished and cannot show that microplastics cause cancer. But it adds to a fast-growing pile of evidence that the particles are reaching deep into human tissue.
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What the researchers found
Dr. Ilias Dimeas of University College Dublin School of Medicine and the University of Thessaly in Greece led the team.
Patients were sampled during bronchoscopy at University Hospital of Larissa, using a lung-wash technique and, in half of cases, tissue biopsies.
Across the 100 patients, the team identified 232 plastic particles. Roughly 70 percent of participants had detectable microplastics in at least one sample.
Among lung cancer patients, 66 percent had microplastics in the lung-wash fluid, compared with 46 percent of those without cancer.
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Polypropylene and polyethylene, the plastics used in packaging, textiles and household goods, were the most common types.
"Microplastics have become an unavoidable part of our environment, but we still know remarkably little about what happens once they enter the human body," Dimeas said in a statement released with the study.
Association is not causation
The researchers themselves flagged the key caveat. Higher microplastic loads in cancerous lungs do not mean the plastics caused the tumors.
Diseased tissue may simply hold on to particles differently than healthy tissue.
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"Microplastics could contribute to inflammation or other biological processes that may contribute to diseases like cancer, but it is also possible that diseased lungs simply retain particles differently than healthy lungs," Dimeas said.
Dr. Ria Devereux, an Environmental Research Fellow at the University of East London's Sustainability Research Institute, described the work as a preliminary study that others can build on.
She also noted the sample was small and that only 50 of the 100 participants had both airway fluid and lung tissue analyzed.
Where microplastics have been found
Microplastics have now been detected in nearly every part of the body researchers have examined, including human brain tissue, blood, placenta and testicles.
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Whether they cause harm at the levels most people carry is still an open question.
Lung cancer remains the leading cause of cancer death in the United States.
The American Cancer Society projects about 229,410 new cases and 124,990 deaths in 2026.
Smoking is by far the largest single risk factor, though 1 in 5 US lung cancer deaths hits a never-smoker.
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Outdoor air pollution has been classified as a cause of lung cancer by the World Health Organization's cancer agency.
What comes next
Dimeas said his lab is now running experiments on how plastic particles interact with lung cells.
The findings are being presented at ERS Congress 2026, which runs September 5 to 9 in Barcelona and online.
Anyone with a persistent cough, chest pain, unexplained weight loss or coughing up blood should see a doctor, particularly if they smoke or have smoked in the past.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.