The term cancer is one that is often associated with dread and foreboding. The cancer statistics we frequently hear about can be quite shocking. In 2014, 356,860 new cases of cancer were reported in the UK, with 163,444 deaths recorded (Cancer Research UK, 2017). 1 in 2 people will develop cancer over the course of a lifetime. But things are changing and 50% of people with cancer now survive cancer for ten years or more. But what is cancer and how does it develop? The term, in fact, refers to a group of over 200 diseases, which are characterised by abnormal and uncontrollable growth in a single cell or in a small group of cells. Some cancers have the potential to spread to other tissues, others not. Most cancers arise from acquired gene mutation over many years, whilst a smaller number are inherited. In this lecture, we will explore the epidemiology and nature of cancer, reviewing some the known risk factors associated with its major types. We will examine the biological and genetic mechanisms that underpin major types of cancer, moving into modern theories of immune dysfunction and epigenetic changes to DNA and its associated proteins. Finally, we will consider existing treatments such as traditional chemotherapy and monoclonal antibody therapy in terms of their biological mechanisms, moving to treatments on the horizon. This lecture is intended to be a primer in the biological basis of cancer and will aim to deal it in a sensitive but direct manner.