Primary human central nervous system tumors represent an incredibly difficult clinical challenge.at one time the obstacles to clinical treatment seemed so overwhelming that there were many who felt that basic research into the biology of human brain tumors was likely to be unrewarding.Primary human central nervous system tumors represent an incredibly difficult clinical challenge.at one time the obstacles to clinical treatment seemed so overwhelming that there were many who felt that basic research into the biology of human brain tumors was likely to be unrewarding.