Hi and welcome to the Chiari forum.
Chiari is a congenital condition that occurs in utero....it is not the result of cancer.
There is no limits on life expectations with Chiari alone....as it effects each of us differently....you will need more testing to see how your Chiari is affecting you and you over all health.
A neck brace may be helpful if you have cranial cervio instability...but not all of those with Chiari have it or are helped with a brace.
Some with Chiari do have other issues related or non related ...so we have to look at our families medical history as well as looking to see what all is going on...those that have Ehlers-Danlos may have more of an issue with low levels of vitamins and minerals.....
We do have a list of anti inflammatory foods-
http://www.medhelp.org/health_pages/Neurological-Disorders/Anti-inflammatory-Foods/show/1023?cid=186