In this video, we're going to begin our introduction to cancer. And so cancer is a disease characterized by uncontrollable cell division is going to lead to the development of malignant tumors. Now a tumor is defined as an overgrowth of cells, or in other words, an abnormal mass of tissue. And tumors typically can cause health complications, and there are 2 main types of tumors that you should be familiar with. The first main type of tumor is malignant tumors, which are an overgrowth of cancer cells that migrate or, in other words, metastasize to other organs. And malignant tumors are the ones that are the most dangerous because they can create a tumor in one area of the body, but then they can migrate or metastasize to a completely different organ within the body and also cause health complications in that other organ. Now benign tumors are the second type of tumor, and these are not cancerous. This is an overgrowth of cells that are not cancer cells, and they do not migrate, so they do not metastasize. Instead, benign tumors remain at the same site. And benign tumors can cause health complications, but they're not nearly as dangerous as malignant tumors are. And now below in our image, notice over here on the far left we're showing you malignant tumors, and over here on the far right, we're showing you benign tumors. So again, the malignant tumors are cancerous, and the benign tumors over here on this side are noncancerous cells. Now, the malignant tumors, that are cancerous, are actually nonencapsulated, and the benign tumors over here, are actually encapsulated. And the capsule is just this basically structure of tissue that can surround and encapsulate the cells, basically containing them in the same area. Now, malignant tumors tend to be very fast growing. They divide very fast since they are cancerous cells, whereas benign tumors are more slow-growing. And then in terms of metastasizing or migrating to other areas of the body, of course, malignant tumors are characterized by migration or metastasis. So this is, of course, going to be, yes, they do metastasize. Whereas the benign tumors, on the other hand, in terms of do they metastasize, the answer to this would be no, they do not metastasize, and partially because they are encapsulated. And so, this here concludes our introduction to cancer and the difference between malignant tumors and benign tumors. And in our next lesson video, we'll get to talk a little bit more about cancer by talking about specific genes that control the cell cycle. So I'll see you all in that video.