will a new health insurance covers an existing medical condition?

My uncle lost his job last year 'cause of cancer surgery and long months of chemo. He's better now, on remission and is looking for a new job. Is it considered pre existing condition to be covered by a new health insurance? He never lost his insurance, he's covered from his old employer but it will end soon. Will he look for another job or go back to his old employer and find an open position?
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Most group insurances cover pre-existing conditions, but it depends on the employer. This is something he needs to ask during the interview process.
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