External signals are transmitted to the cells through receptors activating signal transduction pathways. These pathways form a complicated interconnected network, which is able to answer to different stimuli. Here we analyze an important pathway for oncogenesis namely RAS/MAPK signal transduction pathway. We show that the interaction of the elements of this pathway induces topological structure in the element set and that the knowledge of the topology simplifies the analysis of the set. With a computer algorithm, we isolate from a large and complex group, smaller, independent, more manageable subsets, and build their hierarchy. Subsets introduction makes easier the search for attractors in discrete dynamical system, it permits the prediction of final states for elements involved in signal transduction pathways.