we all have certain amount of different elements including metal in our body but when we say carbon base, we are saying case that is the highest quantity in our body, I think around 20%
Having said that, there are certain things that we can be sure of, like our base cannot be metallic cause it can expand and contract. It cannot be of element of higher atomic weight (i.e. the elements that dont exist on earth) cause those elements are unstable and easily break up into 2 elements of lower atomic weight, so a long lasting life form cannot be comprised of unstable elements.
Then again we are made out of stardust, an ingredient that is common around the universe, so any noticeable life cannot be formed out of any exotic element if that element is indeed exotic or rare.
my scientific 2 cents that can actually be a total crap