I had the same problem Linda last year doing a Caribbean cruise out of Miami. Couldn't get insurance so took the cruise and carried the risk.
I'm not letting this disease stop me enjoying holidays. My wife has said no more long haul trips but she's relented again and we're off to South Africa in January, again with me carrying the risk.
I agree with you about fellow cruisers, many look on their last legs get insurance but cancer sufferers with spread have great difficulty getting cover.