Heavy smokers with knee arthritis may be experiencing an early sign of a difficult-to-treat lung cancer, research shows. Researchers at Prato Hospital in Italy reviewed the case files of 296 patients with inflammation in one knee between 2000 and 2005.

In just under 2 percent of these patients, the mild knee arthritis was accompanied by non-small cell lung cancer. All patients were middle-aged men who had been heavy smokers for most of their lives. Once the cancer tissue was surgically removed, the knee pain cleared up as well. About 85 percent of all lung cancers are non-small cell lung cancer, according to the American Cancer Society. Unless it is caught early, non-small cell lung cancer is difficult to treat. It spreads to the bones in one in five cases and is well advanced by the time it is diagnosed in half of all cases.

Writing in the September issue of The Annals of Rheumatic Diseases, the researchers noted that early warning signs such as knee pain could lead to earlier diagnosis and more successful treatments.

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