Cancer can occur in any part of the body since cells are constantly growing everywhere. Cancer occurs “when cells grow out of control” and continue “growing and making new cells” (1). The term cancer is a very general term that can be specified to a specific kind of cancer. Some examples of cancers include breast cancer, lung cancer, melanoma (skin cancer), leukemia (cancer in the blood and/or bone marrow), brain cancer, etc. Although the name can describe what kind of cancer the patient might have, that does not mean that the cancer is forever localized to that one location. If not treated or detected early enough, cancer can metastasize to other parts of the body. Before I continue to the more in-depth characteristics to developing cancer, here are some defined key terms:
Mutation (2):
A mutation is when there is a change in the DNA sequence, which could be caused by a mistake that occurred when the DNA was being created or by an environmental factor. A mutation does not always guarantee that something bad has happened, sometimes a mutation in the DNA sequence could have no effect on the individual, but it all depends on the location and what mutation actually occurred in the DNA sequence.
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The image above has one example of a mutation, a point mutation (other types of mutations include insertion, deletion, substitution, and inversion). As you can see, there is a single nucleotide change from the original sequence to the point mutation sequence. The original sequence has C →T→G while the point mutation has C→C→G.
Proto-oncogene (3):
This kind of gene allows your cells to divide and grow normally.
Oncogenes (3):
This type of gene is a mutated or bad version of a proto-oncogene. An oncogene is what causes cells to grow and divide out of control which can eventually create malignant (cancerous) tumors.
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The image above shows the cell cycle of a normal cell in one’s body. The G1 phase is where the cycle technically starts. In this phase, the cellular contents will be duplicated so that when the original cell becomes two daughter cells, there will be enough materials to be divided amongst them. Also in this phase, the cell will grow in size. Once the cell has completed the necessary tasks in G1, it can move on to the S-phase. This phase is where the chromosomes are duplicated and where the centrosome is created. The centrosome is an organelle that creates the spindle fibers near the nucleus so that a single sister chromatid can separate to either side of the cell. Once all of the chromosomes are duplicated, the cell will enter G2 (4). In this phase, the cell will continue to grow, make proteins and organelles, and will reorganize its materials so that it can begin the M-phase.
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| https://www2.le.ac.uk/projects/vgec/highereducation/topics/cellcycle-mitosis-meiosis |
The M-phase, or mitosis, is where the cell actually begins dividing. Interphase (G1, S, and G2) is the necessary preparation in order for the cell to divide. The division of the cell will begin in prophase. This phase is the longest phase, taking up about half of mitosis. In this phase, the nuclear membrane will break down, the microtubules will start to appear, and the chromosomes will condense, forming a single compacted structure in the cell. Next, the cell will enter prometaphase. In this phase, the chromosomes begin lining up in the middle of the cell, preparing for metaphase. Metaphase is when the chromosomes are all aligned in the middle of the cell and the spindle fibers have attached to the kinetochore. At the end of metaphase, anaphase will begin. Anaphase is the shortest stage in mitosis and in this phase, the spindle fibers will split the sister chromatids and move them to either side of the cell. Finally, the cell will enter telophase. In this phase, two nuclear membranes will reform around each group of chromosomes and the spindle fibers will disappear. The last event to occur is the actual division and separation of the original cell to the two daughter cells. This event is called cytokinesis (4). Below is a video to give you a better representation of how the cell cycle/ division occurs:
https://youtu.be/_aQXhors-OE
Once the two daughter cells have formed, each will either restart the cell cycle at G1 and divide into two new daughter cells or will exit the cell cycle, otherwise known as G0. When a cell undergoes G0, it no longer needs to divide (even though the cell can re-enter the cell cycle at a later time if necessary) and can begin working (such as a daughter cell becoming a red blood cell). So, what actually causes cancer then? There are several risk factors associated with having cancer, such as genetics, age, diet, sunlight, tobacco, radiation, etc (5). Cancer can be caused by a mutation in the DNA, such as in melanoma (which you can read more about in my previous post), and cancer can also be caused by a mistake that occurs during the cell cycle. Generally, if a cell is formed incorrectly, it will undergo programmed cell death. Cancer forms if/when that incorrect cell continues replicating and dividing rapidly (meaning it didn't die).
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| https://gfycat.com/accuratewholekinglet |
From the GIF above, on the left is a healthy cell dividing at a steady/constant rate, while the cancer cell on the right is dividing rapidly and on top of each other (creating a tumor). This process is the reason why cancer is so hard to treat. Cancer is not similar to a bacteria or virus infecting a specific part of the body, cancer is random and starts in different places in different people. For this reason, it’s hard to find a cure when there are too many targets to consider! Cancer results from 4-6 mutations and those mutations are different depending on the type of cancer, meaning that the mutations in melanoma are not the same as the mutations you could find in breast cancer or lung cancer. Therefore one form of cancer can have thousands of related genetic diseases.
There are two different forms of tumors: benign and malignant. A benign tumor is a non-cancerous growth of cells that will not invade neighboring tissues. A malignant tumor is cancerous and will invade neighboring tissues. This tumor will continue growing and can metastasize (spread) to other parts of the body. A tumor can help doctors determine the stage of a patients cancer. Why is knowing the stage of cancer important? Knowing the stage of the cancer can help the doctor determine a mode of treatment and prognosis for the patient. The stages of cancer are (6):
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| https://thetruthaboutcancer.com/understanding-four-stages-cancer/ Here is an image to help you visualize the 4 stages of cancer. Stage 0 being on the left and stage 4 being on the right. |
Stage 0: This stage of cancer is highly curable. In this stage, the cancer is only at the original location, meaning that surgery can easily remove the benign tumor.
Stage 1: This early stage of cancer can still be curable through means of surgery because it has not spread to nearby lymph nodes or tissues. The tumor has slightly grown since stage 0.
Stage 2 and 3: These two stages are very similar in that the tumor has grown more than stage 1 or 0 but has started to spread to nearby tissues and lymph nodes.
Stage 4: In this stage, the cancer has spread to nearby lymph nodes, tissues, and organs. This stage is when the cancer has metastasized (spread) to other parts of the body. This stage is very hard to cure because of how advanced and spread out the cancer could be.
In order for a doctor to cure any form of cancer, he or she must first determine the type of cancer the patient has, the stage at which the cancer is in, and then the best mode of treatment needed to fight that cancer. Some treatments used in modern medicine include surgery, chemotherapy, etc. In next week’s post, I will be including treatments and treatment rates on cancer patients with a primary emphasis on melanoma.
References:
1) This website provides a general understanding of cancer. American Cancer Society. What is Cancer? https://www.cancer.org/cancer/cancer-basics/what-is-cancer.html. Reviewed December 8, 2015. Accessed April 17, 2019.
2) This website provides about information about different mutations that can occur in the DNA. Your Genome. What is a Mutation? https://www.yourgenome.org/facts/what-is-a-mutation. Accessed April 17, 2019.
3) This website describes what oncogenes and tumor suppressor genes are and how they are associated with cancer. American Cancer Society. Oncogenes and tumor suppressor genes. https://www.cancer.org/cancer/cancer-causes/genetics/genes-and-cancer/oncogenes-tumor-suppressor-genes.html. Accessed April 17, 2019.
4) This website provides an in-depth evaluation of the cell cycle and its phases. Khan Academy. Phases of the cell cycle. https://www.khanacademy.org/science/biology/cellular-molecular-biology/mitosis/a/cell-cycle-phases. Accessed April 18, 2019.
5) This website describes the risk factors that can be associated with cancer. National Cancer Institute. Risk Factors for Cancer. https://www.cancer.gov/about-cancer/causes-prevention/risk. Updated December 23, 2015. Accessed April 18, 2019.
6) This website describes the different stages of cancer and how doctors are able to determine the stage of a cancer patient. Approved by the Cancer.Net Editorial Board. Cancer.Net. Stages of Cancer. https://www.cancer.net/navigating-cancer-care/diagnosing-cancer/stages-cancer. Updated 03/2018. Accessed April 20, 2019.
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