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Dr. Andy Connolly shows Sal what cancerous colon tissue looks like. Created by Sal Khan.
Video transcript
SAL: This is Sal, and I'm still at Stanford Medical School with Dr. Connolly. DOCTOR CONNOLLY: Sal, we're going to continue going. You going to get one unit of credit for today. SAL: Excellent. My mother would be proud. DOCTOR CONNOLLY: So what we're going to look at today is a colon polyp. We had said before polyp is something that's going to stick up like this. SAL: So in that last video we saw, it was not a polyp. That was like an irritated part of the bowel? DOCTOR CONNOLLY: Yeah. It was very low lying. It was-- SAL: Let me get you the pen here. We've got it all tangled up. DOCTOR CONNOLLY: It was really just kind of a patch of irritant right there. SAL: I see. DOCTOR CONNOLLY: So we've got a bigger piece now. SAL: I see. That's why it just looks-- everything is more-- DOCTOR CONNOLLY: So you can see the glands look tiny in here. SAL: So roughly that last slide, how big would it be on this? DOCTOR CONNOLLY: It would be about a piece like that. To be fair, it probably was what was underlying this area right here. SAL: I see. DOCTOR CONNOLLY: And then it grew on to be something more than that. SAL: It wasn't this exact one. DOCTOR CONNOLLY: No, it wasn't. SAL: It could grow on to be something like this polyp. DOCTOR CONNOLLY: It could grow into this. So this is something where when we have a colon resection, if there's a cancer, often there's a polyp. SAL: Right. DOCTOR CONNOLLY: There's an area of that patch like we saw with hyperplasia. SAL: Not necessarily where the cancer is? It's in that same section of colon. DOCTOR CONNOLLY: Yeah. We find that people, if they have colon cancer, often they have lots of other pre-cancer lesions. And you can see-- SAL: I see. Their bowels are just going through a lot of trauma. DOCTOR CONNOLLY: Some of it's familial susceptibility, but a lot of it is that they are showing a propensity to this. I don't know if it's from environmental exposures or what. SAL: I see. And just to remind myself on what we're doing here, so you cut out a bit of colon-- you can kind of view it as a tube-- because there was some cancer there. DOCTOR CONNOLLY: Right. SAL: And then this thing might be some other polyp that's sitting in that same section you cut out. DOCTOR CONNOLLY: Yeah. SAL: And maybe that second slide we saw with the irritation, that could be like right there. I see. DOCTOR CONNOLLY: As matter of fact, it's important that you normally wouldn't see this slide in a patient, because almost all polyps, the colonoscopist is coming in. And they remove it through the colonoscope. SAL: I see, because they don't know whether it's cancerous or not. DOCTOR CONNOLLY: They'll remove it, but you wouldn't see the full wall. So right out here-- I mean, that's all the way through the wall and which you've got muscle up here. SAL: I see DOCTOR CONNOLLY: That's the muscular part of the wall. And so this is, really, kind of going down to a full piece of the wall. SAL: I see. Wow. DOCTOR CONNOLLY: So this is a larger piece, and this is in order to show the polyp in its natural environment. So what we're going to do is we're going to begin looking at the polyp here. And so we'll first start way out here, which is to go back again to the normal architecture. SAL: Right. DOCTOR CONNOLLY: So we had said there are supposed to be tubes. Luckily, this one, it's cut right down the middle of the tube. So you can see how big the hole is supposed to be. And so this is normal architecture there. And then if I just go out a little bit and I'm just going to come along, you can see that you have an area here in which there was a bit of irritation. So it's thrown up a little bit like we saw before, but the real trouble is this thing sticking out. SAL: Right. DOCTOR CONNOLLY: And we wonder what is that thing sticking out. And so for the medical students, we try to tell them to think like the way the pathologist would be, that you first need to look at the overall architecture. This is an abnormal architecture. SAL: Yes. DOCTOR CONNOLLY: You don't usually have bumps sticking out. Then the next thing you're going to do-- SAL: In 3D it would look like a mushroom? DOCTOR CONNOLLY: Yeah. So it would look like a mushroom. Actually, they tend to have foldings on the top of them, so a little more like cauliflower, because they tend to be cauliflower colored. SAL: I see. DOCTOR CONNOLLY: So then when you look here-- SAL: That color, too? DOCTOR CONNOLLY: Yeah. They don't have much color to them. In fact, the colonoscopist, when they look at a polyp, can kind of tell if there's a chance of cancer, because they begin having weird blood vessel samples. SAL: And just to be clear, they're not this purplish color that we're seeing on this slide. DOCTOR CONNOLLY: No. SAL: This is color added. DOCTOR CONNOLLY: Thin section and we had to put the-- it would be colorless otherwise, so we had to put a stain on it. SAL: Right, right. Makes sense. DOCTOR CONNOLLY: So now what I'm going to do is I'm going to draw the area where I'm going to do a comparison. See this thingamabob here? SAL: Yeah. DOCTOR CONNOLLY: You're going too-- SAL: Look at that. DOCTOR CONNOLLY: So now-- SAL: Miracles of science. DOCTOR CONNOLLY: Yeah. SAL: Technology. DOCTOR CONNOLLY: So these are cells which are relatively normal. These are cells which are abnormal. And when we look them, a pathologist immediately says these look angry. SAL: They do. I would say that, too. DOCTOR CONNOLLY: And so when you look-- so what's angry about them is, first of all, they're not committed to behaving. Proper behavior over here. Nuclei belong at the bottom. Things that you're supposed to do for your job, J-O-B, are at the top. SAL: Yes. DOCTOR CONNOLLY: And so when you look at these guys, it's like, where's your job? And so a few of them are making mucin, but these ones have nuclei of different sizes and shapes. SAL: Yeah. And they're all just-- DOCTOR CONNOLLY: They're just doing their own thing. SAL: They're not even doing mucin. DOCTOR CONNOLLY: No, some make mucin, but a lot of them all they're doing is growing. And so usually there's a playoff between that if you're committed to your specific job-- and we call it differentiation. SAL: Right, right. DOCTOR CONNOLLY: So if you're committed to your differentiation, you tend not to have as much propensity to grow. And if you tend to grow a lot, you tend not to do the differentiation. And so this is largely that you have this sort of chaos of nuclei, less commitment to the normal structures. And you're not producing as much. And so what this, this is now called dysplasia. SAL: Dysplasia. DOCTOR CONNOLLY: D-Y-S. SAL: Right, plasia in the wrong thing. DOCTOR CONNOLLY: So it's the wrong growth. And so that's what we're saying is we don't like the looks of these ones, and so these individual cells look dysplastic and they grow. So then to tell whether it's cancer, cancer means in this organ that you've grown across this line in the sand. SAL: So let me-- so literally if you've crossed this boundary right over here, cancer? DOCTOR CONNOLLY: Right. SAL: So even if I'm in the polyp up here and I'm controlling uncontrollably cancer cells and it's mutated and it's not killing itself the way it's supposed to, you still would not call it officially cancer? DOCTOR CONNOLLY: No. So what happens is that there's a middle term where it's a cancer still in the usual place, and that's carcinoma in situ. SAL: I see. DOCTOR CONNOLLY: So carcinoma in situ means it's not an invasive cancer. And therefore, most people would not really call it a cancer. It's just so wild looking up here, you know that it would do that if it was given any chance or time. SAL: I see. So what we're saying is if something was out here, carcinoma in situ, that eventually it probably would make its way. DOCTOR CONNOLLY: Yeah. It just looks so committed to growth and so aggressive and so little differentiation that you know if you gave it time, you'd worry that it would grow. SAL: Makes sense. DOCTOR CONNOLLY: So with here though, this is dysplasia, where it's very upsetting that it's growing so fast. But what's important about this is in hyperplasia, if you took away the stimulus or irritant, it would go back to normal. This will not. SAL: I see. Like we said, if there's some irritant unless we do-- like a week later, we had a couple weeks later that hyperplasia would go away. Dysplasia is here to stay. DOCTOR CONNOLLY: That's right. And so the key word we use is autonomous. SAL: Autonomous. It's independent. DOCTOR CONNOLLY: It's just whatever. So it will grow no matter what. It doesn't care about clues from neighboring cells. It doesn't need something driving it. So what you have then is this is growing. And if it's growing and it's all by itself and growing, it's then called a neoplasia. So that's our last plasia. SAL: So neoplasia showing dysplasia-- DOCTOR CONNOLLY: Yep. So dysplasia just is more of when you go in to look at these guys, these features-- SAL: Oh. It's like a particular feature. DOCTOR CONNOLLY: These cells aren't growing right. SAL: So that's an example of dysplasia. DOCTOR CONNOLLY: Right. That's dysplasia. And then overall, this lump is a new growth. SAL: New growth, neo. DOCTOR CONNOLLY: It's a new plasia, and we you reserve it in the medical field for meaning it's growing on its own. SAL: And how do we know it's new? Because as you said, it sticks around like the hyperplasia. So how do we know this wasn't around for a year? DOCTOR CONNOLLY: Oh, it probably was. So I think it actually came from an area here. And the thinking would be that you probably had irritants or hyperplasia. It would continue to grow. Cells divide. Cells divide too much, and then one of them made a mistake. And so then it clicked on something where it would say, you know what, from now on I'm not listening to any clues. SAL: And then all of its descendants were crazy, too. DOCTOR CONNOLLY: That's right. So then it would then have a real mean streak, and so then they would grow from here. So this is an area where you can see-- SAL: I see that pattern in my own family. DOCTOR CONNOLLY: Yeah, exactly. So then here, these are more normal glands. But even these, that's dysplasia. So these are growing, and they do not have a good pattern of growth. And overall, this lump is a neoplasia. SAL: I see. So when we say new, it's kind of newer than the other tissue. DOCTOR CONNOLLY: Yeah. We don't really mean so much the new for-- meaning that's new as much as its own thing. New kid on the block. SAL: OK. DOCTOR CONNOLLY: So this is the neoplasia. So this one here is a polyp. It has features of dysplasia, but we would say we see no cancer. SAL: How would you know that? DOCTOR CONNOLLY: And so-- SAL: Right, because it never crossed a boundary line. DOCTOR CONNOLLY: And there's a reason why the boundary is important, is that if you look here, these are all the surface cells. Down here, these are the vessels that go to the rest of the body. These are blood vessels. These ones are called lymphatics, and what lymphatics are is they just take the clear fluid around there. SAL: So these right here are the lymphatics, the clear fluid. Fluid can go back and forth between blood vessels and the lymph system? DOCTOR CONNOLLY: Yeah. Usually what happens is that blood comes in an artery like this, goes on down to these little vessels. And then a little bit of the clear parts of it will kind of leak out into it. SAL: The red blood cells are too big, kind of leak out. DOCTOR CONNOLLY: Yeah. So then the lymph is the clear stuff that comes out. And then this is how it gets back to the rest of your body are through these lymphatics, so you can see you do not want neoplastic cells in the-- SAL: Right, because once they're in there, they can get to any part of the body. DOCTOR CONNOLLY: Go anyplace. And then guess what. Set up shop. New kids on the block. They just do what they want. SAL: Mis-mis-stas. I can't say the word. DOCTOR CONNOLLY: Metastasis. So metastasis would be if it gets into these things, it can get out of the colon in a hurry. SAL: Go anywhere in the body, right. DOCTOR CONNOLLY: So this is one where it is not cancer, and it has not invaded these areas where it gets the rest of the body. SAL: Fascinating.