Hi. In this video, I'm going to be telling you about an overview of cancer. So what is cancer? Cancer is a disease; we're probably all familiar with it, but it's caused from misregulated or unregulated cell division. And the cell division occurs rapidly, usually way too much, and because there are all these cells dividing, which shouldn't be, it forms these structures known as tumors. These are just kind of big cell masses from a bunch of cells that have just, you know, continued to divide after they should have.
Now there are two types, probably familiar with these terms. The first is benign, and this is a tumor that remains confined to its original location. So there's a tumor there, but it's just sort of, you know, living its own life even if it shouldn't be there. It's not really bothering anything around it. Then you have malignant tumors, which are very different because malignant tumors start to invade surrounding tissues and can actually spread throughout the entire body into very distant organs and tissues, and this is called metastasis. So there are three main types of cancers. Now obviously, each one of these types has so many different cancer subtypes within them, but just to give you an idea, we have carcinomas, and these are going to be cancers found in epithelial cells, the overwhelming majority of all cancers. Then you have leukemias or lymphomas, and these are cancers of the blood for leukemia or the immune system for lymphoma, and a much smaller proportion here, 7%. And then you have sarcomas, and these are cancers of connective tissue, and these are extremely rare. They do happen, of course, they're on here, but they're, I mean if we add this up, that's around 3% of the rest of the cancers.
So here's an example. Here, benign tumor, and you can see the tumor here in red. It's nicely confined. It's just this nice clean circle, and you can go in there and cut that out and, you know, for the most part it would be all fine. But the malignant tumor looks much worse; it has much more jagged regions that started to invade into surrounding tissues, and obviously, it's not going to be good for the patient with the malignant tumor.
So about cancer, what causes cancer? Well, cancer can be caused by many factors. We'll go over a few of these in other videos. We just want to hit it real quick here. So the first term that we're probably most familiar with is carcinogens, and these are substances that cause cancer. Things like tobacco, which is associated with 30% of all cancers. I mean, think of how might how few we'd have 30% less cancer if we got rid of tobacco since tobacco is known to cause cancer. And so we figure out carcinogens, and we identify, you know, what things cause cancer and what things don't through a field of study called epidemiology. You may be familiar with this if you've done anything with public health, but epidemiology is a scientific field that studies diseases in human populations. So for the epidemiologists that study cancer, a lot of times what they do is they look into, you know, the United States population or, you know, your state population and say, okay, what is everyone doing and which one of these things are causing cancer. So those are called carcinogens.
Now the important thing to realize here is that we know typically that cancer is caused by DNA mutations, but, cancer is not really caused by one mutation. Usually, a bunch of mutations have to accumulate in order to cause cancer. So, we call this tumor initiation when some type of genetic alterations or mutation leads to abnormal cell proliferation or replication. So notice I did say cancer here. This is abnormal cell proliferation. Right? And that's usually how cancer begins, but it's not cancer yet. It hasn't formed cancer until it's formed a tumor and has needs a variety of different properties, which we'll talk about. But, tumor initiators, you know, can actually be handled by the body sometimes even if they're leading to cell proliferation. But what happens is then you get tumor progression, and that is when the tumor cells gain more mutations. Because you're getting more mutations, you're already over-proliferating. These mutations accumulate and that allows these cells to really divide unchecked, and that causes tumors. Now the mutations are generally found within two types of genes. We'll just give an overview. I'll talk more about them later. But the first is called an oncogene. Now an oncogene is a gene that when it's mutated, okay, so oncogenes are mutated genes that cause cell growth. When it is before it's really become an oncogene, we call it a proto-oncogene, and this is a gene that can very easily become an oncogene if it has additional mutations. So oncogenes, mutated genes that cause cell growth, and tumor suppressors are genes that normally, so when they're not mutated, suppress cell growth. And so, obviously, when you mutate that, you mess up that suppression and can lead to cell growth as well.
So here we have an example of this. This is an oncogene. So we have some kind of cancer-causing agent. Do you remember what we call these? Right. So these are going to be carcinogens and they somehow enter into the cell, they come in, they hit the DNA, and they cause DNA damage. So here we have a mutated gene. And so this is we call this a proto-onc. So this is a gene that has a mutation. It can very easily become an oncogene, and now you see that it has, it either gets more damage or there's something weird happens to it. This now becomes an activated oncogene and that can lead to the development of a cancerous stem.
So, tumor cells have a variety of characteristics which we use to determine whether or not they're cancerous. So tumor cells present with certain characteristics. The first is we say tumor cells are genetically unstable. So what that means is that they accumulate mutations at a very rapid rate. So our cells normally, you know, really hate accumulating mutations, and they don't do it, essentially, or else we would be covered in tumors all the time. But cancer cells accumulate a lot of mutations because they're genetically unstable and can do that. We also refer to tumor cells via contact inhibition. So what contact inhibition means is that cells have contact inhibition. So when cells grow and they eventually grow so much that all of their sides are touching other cells. So when their entire plasma membrane is touching other cells, they're going to stop dividing because they realize, oh, I have no place to go because all the sides of me — I'm surrounded by cells. So I'm not going to divide. So they stop dividing when they're touching other cells. That's called contact inhibition. But cancer cells, tumor cells will actually lose contact inhibition. So even though their plasma membranes are surrounded by all these other cells, they continue to divide, and then they just grow on top of each other, and that forms this tumor over time. You may see this in your book as Anchorage-independent growth, but it's the exact same thing. Then, they also have, undergo a term called an angiogenesis. What angiogenesis means, it's the formation of blood vessels. So of course, if you have all these new cells that are growing in a tumor, they're going to need some type of supply of oxygen and nutrients, so you're going to need a blood vessel to get it there. So tumor cells often will undergo angiogenesis and create blood vessels where they shouldn't be to supply those nutrients to the tumors. And then, also, cancer cells and tumor cells have some type of defect in apoptosis or cell death. Right? Because these cells are growing, they're not dying, they're accumulating, forming this tumor, so there's something going on, something wrong with the cell death or the apoptosis pathway. So I know it was a lot of information, but hopefully, it was very simple, just kind an overview of the processes of cancer. So with that, let's now turn the page.
