A friend of my wife's has breast cancer. She's 32. It could have been picked up on a mammography EXCEPT that the insurance company said that she was too young and a mammography wasn't needed. Another friend of hers, younger, is fighting (and losing to) cancer in both breasts for the same reason.

I have had two pre-cancerous polyps removed during a colonoscopy. The prep is awful, but the consequences of NOT having one are worse.