The problem with cancer cells is that they are not foreign invaders, but fifth-column traitors.

FORBES: In search of antigens

This specificity means that the immune system targets foreign invaders without harming the body's normal cells.

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He also suggested that China was buffered from foreign invaders and hence its culture was unhurt.

CNN: ASIANOW - Asiaweek | Letters & Comment

The body produces an inflammatory reaction in response to foreign invaders, such as pollutants.

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Unlike foreign invaders such as bacteria, cancers can often evade immune defences and go unrecognised as a threat.

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Detectors that survive for two days without matching any packets on the network are deemed to be different enough from legitimate strings to be likely to match only foreign invaders.

ECONOMIST: A thousand ills require a thousand cures

The fashion then was for collection and growing foreign species so the Spanish invaders going native was not seen as a problem.

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