Cancer follows a well defined life cycle, the important phases of which are outlined below. Understanding the basics of each phase will help you use the information on this site. Credit to [Jane McLelland](../../CancerPlan/5.%20Resources/People/Jane%20McLelland.md) for my introduction to this general model; it was really helpful in my own understanding of cancer in those first early days. ### 1. Abnormal cell signalling Our body's cells communicate (signalling) with each other as they go through life together. Cell signaling functions like a language, or the traffic lights and turn indicators we use while driving around town in our car. When abnormal signalling occurs, cellular ‘traffic accidents’ occur, which can become cellular mutations. Our immune system cleans up thousands of these "accidents" every day. But some cellular mutations get overlooked by our immune system and stick around. This is the start of cancer, and why a healthy immune system is so important in prevention. ### 2. Abnormal cell metabolism Metabolism is our body's process of generating energy from fuel (sugar, fat and protein) to aid cellular growth and routine body operations. Most of our cells get their fuel from sugar (glucose). But cancer cells have adapted some abnormal metabolizing abilities, designed to give them an advantage and feed their growth and spread through the body. ### 3. Abnormal growth factors Our cells have very strict rules governing when, how and where they grow and naturally die within our bodies. Similar to cell signalling, these rules keep things in order and running smoothly. Cancer has figured out ways to break these cell growth rules. Abnormal growth factors allow cancer cells to grow in places they shouldn't, and create fuel supplies they shouldn't normally have access to. Worst of all, they've found the switch to turn off natural cell death (called [apoptosis](../../CancerPlan/4.%20Lions%20&%20Tigers%20&%20Bears%20(Pathways%20&%20Drivers)/Apoptosis.md)), making themselves immortal! ### 4. Abnormal immune response Under normal circumstances our body's immune system identifies those cellular traffic accidents (eg. baby cancer cells) and clears them out, just like sweeping up spilled popcorn from the kitchen floor. But under *abnormal* circumstances, cancer tricks our immune system into not seeing these errors, leaving the mutated cells alone to continue their growth and spread. Understanding how our immune system works is important because there are ways to "reprogram" it to seek out and kill these cancers cells early in their development. ### 5. Fast cell division One of the hallmarks of cancer cells is their ability to divide (double up and grow) quickly. In the beginning it's at a microscopic level which is hard to notice. Three cells or three thousand cells can all sit on the head of a pin, so that growth is hard to see. But just like the compound interest on our money, when you're doubling something's growth every X period of time, in the later stages that doubling growth effect is huge and can quickly overcome an organ or the entire body. Fast cell division is also closely linked to [chemotherapy](../../CancerPlan/3.%20Treatments/3.6%20%20Standard%20care/Chemotherapy.md), as chemo drugs are specifically designed to seek out and kill fast dividing cells.