The cells of our body depend on signal transduction pathways to carry out different types of cell processes at the right moments in time to basically produce physiological responses to certain types of external stimuli. Now, even though these signal transduction pathways are very, very important to the functionality of our cells, these signal transduction pathways must, must be closely maintained and regulated by ourselves. In fact, the inability of our cells to regulate and terminate these signal transduction pathways can actually lead to tumor growth and eventually cancer. And so in this lecture, what I'd like to focus on is discuss how different types of abnormalities in a signal transduction pathway can actually lead to cancer. Now, before we actually begin our discussion on the abnormality part, let's focus on how normal process takes place and how normally our cells terminate these signal transduction pathways. And to use an example, we're going to focus on the EGF signal transduction pathway where EGF stands for Epidermal growth factor.