Lung cancer is not always as deadly as doctors once thought

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New research suggests lung cancer isn't always as deadly as doctors once thought.

The researchers say almost 1 in 5 lung cancers detected in screening scans are probably so slow-growing that they would never cause problems.

These aren't false-positive results that further testing shows not to be cancer.

These were cancerous tumors -- ones that cause no symptoms and were unlikely ever to become deadly.

The results probably won't change how doctors treat lung cancer.

Usually the disease is diagnosed after symptoms develop, when it's potentially life-threatening.

And doctors don't know how to determine which tumors found on scans might become dangerous, so they automatically treat the cancer aggressively.

The study is in Monday's JAMA Internal Medicine.