 Cancer is unarguably one of the most deadliest diseases that exist on the planet today. It kills on average 7.6 million people worldwide each year. But what causes cancer? When normal cells divide, they undergo a process called a cell cycle which is regulated by the cell's genes, and eventually after the cell divides a certain number of times it can no longer divide and enter apoptosis or cell death. However, every time a cell divides, its DNA undergoes slight mutations in some genes. And over the course of the cell's lifetime, these mutations begin to accumulate with each division. And if these mutations are severe enough, then the cell does not undergo apoptosis. And since the mutations disrupted the cell cycle and prevented the cell from undergoing cell death, the cells begin to divide uncontrollably without stopping. And this is what's known as cancer, the uncontrollable division of cells due to the disruption of the cell cycle. As for the cancer cells, they keep on dividing and dividing until a tumor or a clump of cancer cells form. Now there are two types of tumors. A benign tumor is a tumor that just stays in one area of the body instead of spreading out. As a result, this is not really considered a cancer. However, a malignant tumor is a tumor that spreads throughout the body. This is what's commonly classified as cancer. Now despite the fact that cancer is really, really, really hard to cure, there is actually a treatment that exists. First, the patients go for a screening which is nothing but the use of x-rays and MRIs to locate the tumor. Then the patients undergo surgery to excise as much of the tumor as possible. Then ionizing radiation is used to wipe out any remaining cancer cells that decide the tumor. And then if necessary, the patient undergoes chemotherapy in which anti-cancer drugs are injected into the body which go throughout the body and target cells which are constantly dividing. This is why patients usually go bald during chemotherapy. However, there are certain ways in which you can prevent or delay the onset of cancer. Eating a healthy diet, controlling UV exposure, and most importantly, not smoking. But don't forget there are also thousands of other ways in which you can prevent or delay cancer. I hope this video helped you understand more clearly what cancer is. So don't forget to like, share, and subscribe. So please follow me on Twitter and Google+. Also check out my newly started science community on Google+, in which I will include a link to in the description below. And stay tuned for more science videos.