The present invention relates to a method for predicting the survival time and/or the disease severity in a subject suffering from a disease associated with a loss of p53 function. Here, the inventors established a 13-gene functional p53 score from a sample collection involving genes downregulated upon p53-silencing and they showed that the score directly predicts the survival time in subjects. Moreover, the inventors showed that this method works with the commonly methods used in the prior art for sequencing genes and measuring their expression. Thus, the present invention relates to a method for use in the prevention and/or the treatment of diseases associated with a loss of p53 function in a subject in need thereof.