Are cancer screening worth the stress if you have Alzheimer's disease?

A fellow caregiver asked...

My mother is in late middle stage AD at 83 years old. Her doctor has recommended that, based on her age, she should have several cancer screening tests, including a colonoscopy. I know these invasive tests will be very traumatic for my mother, as she won't understand what is happening and why. I am also not sure how aggressively we would want to treat any illness that was discovered, so I question the value of putting her through so much fear and discomfort. I'd appreciate any feedback from doctors or family members who have dealt with this issue.