Figure 2. In metastatic progression, time and the failure factors indicated in the figure above, play a crucial role in the prognosis and treatment of the patient with cancer, as shown in the model of the linear progression of a tumor. In time, the cells increase in malignancy. Thus the concept of ‘metastasis of metastasis’ is used in reference to the metastasis becoming in the course of time more malignant, resulting in the death of the patient, as the illness cannot be controlled.