An in vitro method of predicting a favorable or poor response to p53 gene therapy for a human subject having a tumor comprising: (a) determining whether tumor cells of said tumor have a mutated p53 gene; and (b) determining whether tumor cells of said tumor express p53 protein at a level that is higher than that expressed in normal p53-expressing non-tumor cells; (i) wherein if said tumor cells are found to express a mutant p53 protein at levels higher than that expressed by normal p53-expressing normal cells, wherein the mutation in the p53 gene is a blocking dominant negative mutation and wherein said mutated p53 is able to bind to and to inactivate normal p53 protein, then such is indicative of a poor response to said therapy and (ii) wherein if said tumor cells are found to express a mutant p53 protein at levels higher than that expressed by normal p53-expressing normal cells and wherein the mutant p53 protein neither binds or inactivates normal p53 protein, then such is indicative of a favorable response to said therapy; and (iii) wherein if said tumor cells are found to not express a mutant p53 protein at levels that are higher than that expressed by normal p53-expressing normal cells, then such is indicative of a favorable response to said therapy. (a) determining whether tumor cells of said tumor have a mutated p53 gene; and (b) determining whether tumor cells of said tumor express p53 protein at a level that is higher than that expressed in normal p53-expressing non-tumor cells; (i) wherein if said tumor cells are found to express a mutant p53 protein at levels higher than that expressed by normal p53-expressing normal cells, wherein the mutation in the p53 gene is a blocking dominant negative mutation and wherein said mutated p53 is able to bind to and to inactivate normal p53 protein, then such is indicative of a poor response to said therapy and (ii) wherein if said tumor cells are found to express a mutant p53 protein at levels higher than that expressed by normal p53-expressing normal cells and wherein the mutant p53 protein neither binds or inactivates normal p53 protein, then such is indicative of a favorable response to said therapy; and (iii) wherein if said tumor cells are found to not express a mutant p53 protein at levels that are higher than that expressed by normal p53-expressing normal cells, then such is indicative of a favorable response to said therapy. (i) wherein if said tumor cells are found to express a mutant p53 protein at levels higher than that expressed by normal p53-expressing normal cells, wherein the mutation in the p53 gene is a blocking dominant negative mutation and wherein said mutated p53 is able to bind to and to inactivate normal p53 protein, then such is indicative of a poor response to said therapy and (ii) wherein if said tumor cells are found to express a mutant p53 protein at levels higher than that expressed by normal p53-expressing normal cells and wherein the mutant p53 protein neither binds or inactivates normal p53 protein, then such is indicative of a favorable response to said therapy; and (iii) wherein if said tumor cells are found to not express a mutant p53 protein at levels that are higher than that expressed by normal p53-expressing normal cells, then such is indicative of a favorable response to said therapy.