"..expected over the next 5 years" = it will grow just like it's doing now! It will spontaneously involute but not over the next 5 years - maybe in 5 years.
You need to acknowledge and discuss the reason for missing. Some people - young women mostly, intentionally restrict insulin therapy to lose weight. It's called diabulimia. They manage their glucose levels right before the blood draw so that their glucose is normal on the labs, but the HA1c doesn't lie.
Prostaglandins increase GI motility due to peristalsis. It's the same reason why the uterus contracts during menstruation.
Some of the cases of cancer in the smoking population will be due to a factor other than smoking. The question is asking about the cases that are due to smoking specifically.