[Question about Disability Review Examination]

I'm a brand new member and a bit lost in all the resources and information.   I would appreciate any advice (or pointing me to a good reference.)    Here's my situation:   I'm 76 years old and a 27-year Army veteran.   I served in Vietnam with an engineer land clearing battalion and was exposed to Agent Orange.   When I retired in 1996 I was given a 20% rating due to skin issues including skin cancer.  I had multiple sign cancers and Mohs surgeries afterward.    Many years later I developed Non-Hodgkin Lymphoma, and the VA rated me at 100%.  The decision letter said the evaluation was "not considered permanent" and would be reviewed after two years.   I recently got a letter telling me I would be contacted to schedule an ACE Exam by telephone.   I'm nervous about this obviously.   My condition is stable, but I expect to see an oncologist for the rest of my life.   Has anyone had a similar situation?  Can anyone offer me advice going forward?  

Thanks very much!