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Voiceover: So, now we can talk about the different types of acute leukemias. And remember that acute leukemias come from these cells. So, the most immature types of blood cells that you can possibly have, and we can split up the acute leukemias into ones that come from myeloid cells, so these cells, so the acute myeloid leukemias, or the leukemias that come from lymphoid cells, so the acute lymphoid leukemias, and we're going to start off by talking about the acute lymphoid leukemias. So, I took that big diagram, and I shrunk it down, and I stuck it into the corner because, to be completely honest, nobody memorizes this diagram by just looking at it one or two times. You have to keep looking at it over and over again, in order for it to stick inside your mind. So, if at any point you're like, what cell is she talking about, just look up at this diagram to help you reorient yourself. So, I said that we were going to start off talking about these guys, so the acute lymphoblastic leukemias. That's often abbreviated ALL, so we don't have to write it all out again. So, one of the things that I really loved about learning the different leukemias was that the name of the leukemia told you a lot of the information that you needed to know about it. So, the word leukemia tells you that you're dealing with a cancer of the blood cells. Well, what type of blood cells? So, this is a lymphoblastic leukemia, so we're dealing with lymphoblasts or immature lymphocytes, immature B and T cells, and just how immature are those cells? So, if this is an acute leukemia, we're dealing with the most immature cells that you could possibly have, and really, that's the majority of the information that you need to know about this disease. A couple of other important things is, number one, ALL is the most common cancer in kids. So, unfortunately, it affects the little ones the most, and it's also associated with Down syndrome, with Down syndrome, and you may know that Down syndrome is a genetic syndrome, where you end up with three copies of chromosome 21, and in a normal cell, you only have two copies of chromosome 21, but in Down syndrome, you end up with an extra copy, so, you end up with three in total, and that's called Trisomy 21. Well, it turns out that chromosome 21 has this gene on it, and that gene makes a protein that can damage DNA. So, the idea is, among other ideas, that because you have an extra gene, you end up with more damage to your DNA, and that increases your risk of getting ALL. So, let's say that you have a patient, a really young patient who's showing signs and symptoms of leukemia, so you go ahead and you get a bone marrow aspiration from him, and if the patient has ALL, you'd expect that when you looked at the aspirate underneath the microscope, you'd see lots of lymphoblasts, because ALL, after all, is just a cancer of lymphoblasts, right? But what do I mean by you'd see a lot of lymphoblasts? Because lymphoblasts look like all of the other immature blood cells. They look exactly the same, and it's not like they're carrying around a sign saying, hey, I'm a lymphoblast, right? Or are they? Well, they kind of are, because remember we said that all lymphoblasts have this protein inside their nucleus called TdT, TdT, and only the lymphoblasts have this, so none of the other blood cells have it, and not even the immature lymphocytes have it. So, it kind of is like a sign that they're carrying around, saying, hey, I'm a lymphoblast. So, if the cells in the aspirate have TdT inside the nucleus, then you can go ahead and diagnose the patient with ALL. So, moving on, since there are two different types of lymphoblasts, you'd think that there would be two different types of ALL, and there are. There are two different types of ALL. The first one is called the B cell, B cell ALL, and the second type is called a T cell ALL. And we're first going to talk about the B cell ALL, so that's this guy over here, and going back to our patient that we did the bone marrow aspiration on, we said that in his aspirate there were lots of lymphoblasts, but how do we tell if that's a T lymphoblast or a B lymphoblast? So, there are lots of markers that only B lymphoblasts will have, and there are other markers that only T lymphoblasts will have. So certainly you could use those markers to tell them apart, but there's another really nifty feature of B cell ALL's that you could use to tell them apart, and that is that B cell ALL's are associated with translocations, so chromosome translocations. So, we know that there are lots of different leukemias that have translocations associated with them, right? But a B cell ALL has two very specific translocations associated with it. The first is a t, t for translocation, t (12;21) translocation, and all that means is that chromosome 12 and chromosome 21 each have a segment that's shifted onto the other chromosome. And the second type is a t(9;22) translocation, and the first, and the t(12;21) is usually found in kids who have B cell ALL, and the t(9;22) is usually found in adults who have B cell ALL. So these translocations are really helpful or super helpful. First, they help us diagnose the disease, and, secondly, they help us determine the prognosis of the disease, and I say that because it turns out that the t(12;21) translocation is associated with a better prognosis, and that's because the leukemia cells that have this translocation inside them, the cells themselves are more responsive to treatment, to chemotherapy, and that's for a whole bunch of scientific reasons, but the way I like to think of it, is that 12 and 21 are mirror images of each other. So, I like to think, I like to imagine that there's a mirror in between them, and this is my really poor attempt at drawing a pistol, a gun, and the gun is shooting therapy, chemotherapy at the mirror, so that leads to this explosion that kills lots of cells around it, and I know it's a really silly way of thinking of it, but for some reason, I haven't been able to forget that 12;21 means better response to therapy, and sometimes a bad analogy is more memorable than a good analogy, okay? So, that's B cell ALL. Now, the other type of acute lymphoblastic leukemia is a T cell ALL. So, now we're talking about this guy over here, and I want to start by asking you, when the bone marrow releases T cells into the circulation, into the blood, where do the T cells go? Well, usually, they go right into the thymus, and they go there so that they can develop a little bit more. So, in T cell ALL, you have lots of T lymphoblasts in the blood, and they can also go to the thymus, and if they do, your thymus will get bigger, and it'll feel like there's a mass, a mass inside your thymus, and that's a problem because if your thymus is growing larger, it can compress the structures around it. So, it can compress the airway, and it can compress the esophagus, and that'll lead to a whole slew of symptoms on its own. So, you can get a thymic mass, and the other thing that's important is that T cell ALL's are most often seen in teenagers, and something that might help you remember these three things is remembering the letter T. So, T cell ALL is associated with thymic mass and found in teenagers, okay? So, those are acute lymphoblastic leukemias. Now, let's move on to our acute myeloid leukemias. So, that means in this diagram we're looking at these guys over here. We're looking at the acute myeloid leukemias, myeloid leukemias. And because there are many types of myeloid cells, you can have several different types of acute myeloid leukemias, and then, acute myeloid leukemia is abbreviated AML. So, for example, you could have an acute myeloid leukemia developing from a myeloblast, so this cell over here, and that would give you, and that would be called, an acute myelo- myeloblastic leukemia. You could also have an AML that develops from a monoblast, and that would give you an acute monoblastic leukemia, and in the same way, you could have an AML developing from a megakaryoblast, and that would give you an acute megakaryo- megakaryoblastic leukemia. And you could actually get a leukemia, an acute myeloid leukemia developing from an erythroblast, but that's so extremely rare that you won't really hear people talk about it. It doesn't really happen in the real world, but it's good to know that it's possible, theoretically, right? So, those are all of the different types of acute leukemias. Now, we're ready to talk about the chronic leukemias.