Overview of Cancer

Hi in this video we're gonna be talking about an overview of cancer. So cancer is a disease we're all familiar with it. But essentially the basic definition of cancer is that it is abnormal. Um or it can be unregulated. It's a little bit more difficult term but abnormal cell growth and division. So you're getting a ton of cell growth sales are growing in size and they're dividing. And generally what we term this whole cell growth and division is called proliferation. And in cancer it's unregulated and uncontrolled. It's just going all over the place proliferation which is the cell growth and division. And if you get a lot of cell growth and division eventually that's going to develop into a tumor. But it's not only cell growth and division that is unregulated, it's also unregulated death. And so cell death is called apoptosis. And that is a process that is this whole regulated pathway that tells cells when it's time for them to die. And um unregulated and uncontrolled apoptosis also causes cancer because you're getting these cell growth, you're getting these divisions and nothing's telling them, oh wait, you're growing too much, you're dividing too much, it's time to die. So it's this combination of growth division and unregulated death that allows for these tumors to grow and so in order to affect cell growth division and death, it requires multiple mutation. So a lot of people think, oh cancers one mutation and that leads to cancer, but actually what makes cancer difficult to treat is that it's an accumulation of mutations and those mutations are different for every cancer and for every individual. So we call cancer, you know, a disease, like we say breast cancer. But everyone's breast cancer is different because they all have different mutations in different genes. And there may be some common ones that we're familiar with, like the Bracha, um jeans and breast cancer. Those are very commonly found in breast cancer cells. But each one of those, even if they do contain Bracha, also have to contain other mutations that can vary in different genes in different positions throughout the genome. So these multiple mutations exist. And because there's multiple mutations, we say that cancer cells are genetically unstable and this is a fairly common term that you hear when describing cancer. And so what that means is that there's just a ton of mutations and even chromosome elaboration meaning that there's chromosomal breakage, chromosomal inversions, um sort of transitions these all these different things that we've talked about in different chapters. These are commonly found in cancers. And so we just sort of say, you know, cancer cells have a lot of these, therefore they're genetically unstable. Now there are two types of cancer, assume Urz the first is benign and these are still cancer, right, this is still cancer. It's created a tumor, It has unregulated cell growth division and cell death. But the the I guess the positive part of benign tumors is that they're proliferating abnormally, but they're contained to a single area. So if you have a benign tumor that's causing problems, a surgeon can just go in, chop it out and you may need a little bit of extra cancer therapy. But generally the prognosis or the survival rate of people with benign tumors is extremely high because they're confined to this one area and you can just go and take them out. Whereas malignant tumors are much more dangerous because they metastasize, which means they travel to other areas of the body. So they may have started out in the breasts, but then they go to the brain and that's very dangerous. Or they may have started out in the kneecap and the bone and the kneecap. But then they travel to the liver and it's very difficult because you can't just take out, you know, your kneecap and then also your liver. Um and then also part of your brain because that is very difficult. It's very harmful to your body. You can't just cut out one single benign tumor. Um and expect that to work for a malignant tumor. So an example of this is that this is an organism. You have a benign tumor that has very clear edges here and a surgeon can just come cut this region out and then the cancer is mostly gone. For the most part malignant tumors are much more difficult because if a surgeon comes in, it can cut this much out while you're still left with these regions here that may travel and exist in other organs or elsewhere throughout the body. And it can be very dangerous now to neurogenesis is the term you're going to see. And what that is is it's the development of the tumor, particularly malignant tumor. These tumors that travel to different areas and like other tumors, they require more than one mutation. And generally these mutations that occur often happen in signal transaction pathways. So what our signal transaction pathways, well, you'll learn about them, You probably heard about them at least a little and you'll learn about them in different biology classes, but essentially they're just pathways of proteins that go from one to the next to create some kind of big response at the end and there can be offshoots here of different proteins that they can affect and that can affect different response. So it's these networks of proteins that control cell activities. And a lot of these signal transaction pathways end up controlling gene expression. So you can have imagine if there's a bunch of mutations in the signal transaction pathways that can essentially affect the regulation and the expression of hundreds if not thousands of genes which is obviously very dangerous to the cell and can very easily lead to tumors. And so but the interesting part of cancer is that cancer is considered clonal meaning that it derives from a single cell. So at some point this one cell created have a mutation, then it has more mutations and more mutations and more mutations. Until it's it's created this tumor through just unregulated cell growth and division and unregulated death and that it creates single cell. So we say that cancer is clonal because it comes from this one cell to begin with. And so whatever aberrations, whatever mutations it creates is passed onto progeny cells. And those progeny cells can come up with their own mutation like this one can have a mutation and therefore every time it divides it will have these this one can add another mutation. And so it ends up being this like super genetically diverse tumor where even different regions of the tumor can contain different mutations but they're all um sort of have this unregulated cell growth division and death that allows them to form this tumor. Now there is an interesting type of cell and this is called a cancer stem cell. And these are controversial for a while. Um And they're not found in every cancer but they have been found in a few cancers. And what they are is they're stem cells. And so stem cells just mean that they can proliferate and create more tumor cells but they also have the ability to self renew which means that they produce more of themselves. So if a cancer stem cell divides it's gonna produce one stem cell And 1 to Marcel. And so um this is a major source of um tumor cells because often these cells that have a lot of mutations eventually reached the point where they're no longer dividing. It's just gotten they have so many chromosomal aberrations are so genetically unstable that they can't do anything. They can can't even divide anymore. But these stem cells can keep dividing because they keep producing these same stem cells over and over and so they produce stem cells and tumor cells. And so it helps the tumor continue to grow even after its accumulated so many mutations that it wouldn't normally grow otherwise. So it's this like constant source of just nutrients and just feeding the tumor with more cells through these stem cells. And so there's a new sort of research undergoing right now to figure out how to improve cancer therapies to target these stem cells which we've just really recently found out about to improve the treatment of cancer. So hopefully that will I'm sure we'll be hearing about that more. If you guys go into medicine or research and focus on cancer that will definitely be something that you'll hear about more. So pretty much like the process of cancer is you have one cell remember this is clonal and it creates some type of mutation. Now it says particularly here tumor suppressor gene and we're going to talk about different types of genes and cancers in the next video but for now just know it's mutation in a gene, this cause cells to proliferate. So they're growing and dividing. Sorry about my handwriting. But growing and dividing. Then they get another mutation then they create another mutation. Then they get another mutation in several different genes. And eventually you get this cancer where you can see here that there's different subtypes here of different cancers that look different cells that look differently. And this is because these tumors don't necessarily have all the same cells with all the same mutations there. This um combination of different cells with different mutations depending on at what point they accumulated those cells in the formation or accumulated those mutations in the formation of the tumor. So that is the first little bit of overview of cancer. Now let's move on to some of the causes.

Okay so now let's talk about the causes of cancer. So cancer mutations developed in many different ways. Um One that you may not even be familiar with our viruses can cause cancer. So a big one that hopefully you're familiar with because this vaccine came out during your lifetime. But as HPV and HPV has carries two genes called E six and E. Seven. And these very easily lead to cancer. They don't do it every time but they can. And um so viruses can introduce different genes that can activate cancer causing genes or interfere with the normal cell pathway that leads to cancer very easily. And so um only mentioning HPV here but there are lots of others especially in liver cancer. Um HCV hepatitis C um is another example. There's capacity sarcoma which is found in HIV and AIDS patients. Um but essentially these different viruses can lead to cancer. But the good part about viruses leading to cancer is that you can have vaccines against viruses and therefore there is a vaccine against HPV. It's the only vaccine that currently exists that is a vaccine against cancer. And so it's super amazing. It's an incredible vaccine. And so um this will actually not only prevent you from getting HPV but can prevent overwhelmingly cervical cancer in women but also head neck and throat cancer in men which a lot of people don't know about but viruses can very easily and often cause cancer then a second way is epigenetic changes. So epigenetic changes are changes to the histone protein modifications that are found in the packaging of D. N. A. And we know that different modifications can cause genes to be over expressed or genes to be under expressed. And either way this is resulting in gene this regulation so causing it to not be expressed correctly. And if a gene is over activated or under activated it can affect regulatory genes that are controlling cell growth division and death and that very easily can lead to um cancer. So viruses epigenetic changes and then finally environmental substances. So these are things like cigarette smoke which we definitely know called cancer. It can also be exposure to UV rays from the sun or tanning beds. Um It can be exposure to certain chemicals like asbestos but essentially all these different environmental substances that we encounter all the time um can very easily lead to a mutation or multiple mutations that can accumulate over time if you're exposed to various different ones. And those accumulation of mutations will lead to cancer because they'll affect cell growth division and death. So those are some of the causes of cancer. Now one way that these causes all sort of come in together and really cause cancer is through mis regulation of the cell cycle. And um mis regulation of cell cycle is one way these mutations can forgot what the word was here. Miss regulations. Like one way these mutations can um something in a single cell we're just gonna put effect a single cell. I'm not entirely sure what I was going for there but don't worry about it. And so um essentially mis regulation of the cell cycle is obviously going to affect everything from growth division and death which are the three main facets of cancer. And so how the cell cycle is regulated is actually through different proteins. Some of these proteins are called Cyclones and some of these proteins are called cycling dependent kindnesses. And first do you remember what phoenix is? Right? It's going to add phosphate and when phosphates are added to proteins that can activate more proteins. And so um the cell cycle has these different regions called checkpoints. And at different checkpoints, these proteins called Cyclones and the proteins that depend on Cyclones. The cycling dependent penises are have to be appropriately regulated at these different points to allow the cell cycle to continue. So an example of some of the cell cycle checkpoints include G. One to s so remember the phases of the cell cycle is G one, S. G two, then you have em and then you're back to interface, this is the cell cycle here. So the G one S transition is right here. And this is um a checkpoint that ensures that the D. N. A. Is not damaged, right? Because in S DNA replication occurs and the cell does not want to replicate damage D. N. A. So it stops here and it checks to make sure that the D. N. A. Is right, it's not damaged and if it is damaged it repairs it. And so a important protein that you'll read about that is important in this transition is called retinoblastoma. And we'll talk about this protein a little bit more but in later videos, but essentially this is a transcription factor and what the transcription factors do they regulate gene expression. And so the retinoblastoma transcription factor is really important in the G. One S transition, making sure that the D. N. A. Is appropriately repaired and is correct before replicating it. Second one is G. Two to M. And this is making sure DNA replication has gone correctly. So D. N. A. Was replicated here and now the cell wants to stop before it divides and make sure something hasn't gone incredibly wrong with DNA replication, which makes sense. Right. If your DNA is replicated wrong, then that can induce a lot of different mutations that can very easily lead to cancer. And so um here's a cycling called C. D. C. Two and Cyclone B. And this is the this is the kinetics and this is the cyclone and these are important in these transitions. You don't necessarily need to know these um that's for cell biology for most of you, but just know that these cyclones and the cyclones dependent penises are here. So if we look have this sort of graph the different phases G one phase DNA replication happens here in the S phase G two phase and mitosis. You can see that different cyclones activate at different times where Cyclone E. Is going to really affect the G. One S. Transition where um you know, cycling B for instance will really affect this G two to M. Transition. And there's these different concentrations of cyclones that happen over time and the different concentrations of cycling affect the cyclone dependence, kindnesses that go on to add prostates, two different proteins that say, okay, everything's checked. It's time to move on. Okay we're good with S phase, let's move on. And then it gets to G. Two phase and it's like oh wait we need to do something else, let's start over and it will it will actually go back. It will start over. It will pause and make sure that everything is right before mitosis continues. Now. You can imagine if mutations happen in these regions and these proteins that are regulating these sections or any of the proteins that are going to be added that will have phosphate added to them by the kindnesses. Then this whole system will get messed up. And that is what allows mutations to that accumulate over time to pass through mitosis because it says oh I have a mutation but don't worry about it. We can move on. We don't need to check it and repair it. Oh the DNA wasn't replicated correctly. Oh don't worry about it, we'll move on. We don't have to correct it. And so these impacting these pathways are super important in creating this abnormal growth, proliferation and death and preventing it from happening normal cells. And that leads very easily to cancer. So, no, that was a mouthful. But with that it's an overview of cancer. Let's now move on.

Which of the following is NOT a cause of cancer?

• A. A collection of DNA mutations
• B. Unregulated proliferation
• C. Unregulated apoptosis
• D. A single DNA mutation

Which of the following statements about cancer is false?

• A. Cancer stem cells exist to continue growing the tumor for some cancer types
• B. Cancers are clona
• C. Cancer is triggered only through external mutagens
• D. Cancer can be caused by epigenetic changes

Which of the following are enzymes are responsible for controlling the cell cycle?

• A. G1 cylases
• B. Cyclin-dependent kinases
• C. Bypass polymerases
• D. Ligases