A method for identifying an aggressive cancer or which may develop metastases in a patient affected with breast or colon cancer, and comprising the steps of: - measuring the expression level of the APC11 protein in a sample stemming from said patient, and - classifying the cancer as aggressive or which may develop metastases when a significant difference in the expression level of the APC11 protein is detected with respect to a reference value, said reference value may be: i) an expression threshold value, obtained by determining the number or the proportion of cells which express the APC11 protein or further the amount or intensity of expression of the APC11 protein within samples from patients affected with breast or colon cancer and the subsequent fate of which is known as regards aggressiveness of the cancer, and/or development of metastases, ii) an expression level of the APC11 protein measured in a biological sample from a healthy subject or else affected with the same type of cancer but which is not aggressive or able to metastasize, iii) an average value of the expression level of the APC11 protein which is detected on a pool of biological samples from healthy subjects or else subjects affected with the same type of cancer but which is not aggressive or able to metastasize. - measuring the expression level of the APC11 protein in a sample stemming from said patient, and - classifying the cancer as aggressive or which may develop metastases when a significant difference in the expression level of the APC11 protein is detected with respect to a reference value, said reference value may be: i) an expression threshold value, obtained by determining the number or the proportion of cells which express the APC11 protein or further the amount or intensity of expression of the APC11 protein within samples from patients affected with breast or colon cancer and the subsequent fate of which is known as regards aggressiveness of the cancer, and/or development of metastases, ii) an expression level of the APC11 protein measured in a biological sample from a healthy subject or else affected with the same type of cancer but which is not aggressive or able to metastasize, iii) an average value of the expression level of the APC11 protein which is detected on a pool of biological samples from healthy subjects or else subjects affected with the same type of cancer but which is not aggressive or able to metastasize. i) an expression threshold value, obtained by determining the number or the proportion of cells which express the APC11 protein or further the amount or intensity of expression of the APC11 protein within samples from patients affected with breast or colon cancer and the subsequent fate of which is known as regards aggressiveness of the cancer, and/or development of metastases, ii) an expression level of the APC11 protein measured in a biological sample from a healthy subject or else affected with the same type of cancer but which is not aggressive or able to metastasize, iii) an average value of the expression level of the APC11 protein which is detected on a pool of biological samples from healthy subjects or else subjects affected with the same type of cancer but which is not aggressive or able to metastasize.