Why does Cancer appear?

Your cells are constantly replicating to grow, replace worn-out cells and repair the damage done to the body. During this process, DNA is copied so that each cell gets the same genetic material. This, however, is where the problems begin. During this process, DNA is unwinded and serves as a template to assemble the new DNA. This process sometimes fails to assemble new DNA correctly, so errors are made. The cell has systems to check and repair DNA damage, but sometimes, they miss some or cause even more damage when repairing, resulting in permanent DNA damage. However, not all the damage to DNA causes mutation. Only some do. DNA damage can be done exogenously (from outside of the body), such as by very long exposure to UV, smoking or ingesting carcinogens, and some genes can make you more prone to mutations. [1]

Over the years, this permanent damage to DNA accumulates, and every adult has some permanent damage to their DNA. However, sometimes, the damage to DNA causes mutations to appear. Some mutations are harmless, but some can cause changes in the way a cell operates. Suppose a cell has mutations in the right genes and it acquires all six hallmarks of Cancer (resisting cell death, activating invasion and metastasis, inducing growth of new blood vessels to the cells, evading growth suppressors, enabling to divide infinitely and sustaining proliferative signalling not to rely on body signals to tell them when to grow). In that case, it becomes a tumourigenic cell (able to form tumours). [1]

At some point in your life, you had a Cancer cell in your body, but your immune system successfully killed it before it was able to become a tumour [2,3]. Most of the Cancer cells you develop will be killed without you noticing. The set of interactions between Cancer cells and the immune system is called Cancer Immunoediting, and it has three stages. [2]

Elimination is the first one, where the immune system recognises and kills the Cancer cells effectively before they cause harm. This phase is complete if all the Cancer cells are killed, but the Equilibrium stage begins if some tumour cells are left. [2]

In the Equilibrium stage, the tumour cells are kept in check but not entirely eradicated. In this stage, the Cancer cells stay dormant (inactive) or evolve, obtaining further mutations. As this process continues, the immune cells exert selective pressure by killing susceptible variants of Cancer cells where possible. As this continues, the whole tumour is not eradicated, and the result is that only the cancer cells that can resist, avoid, or suppress the immune system are left. In this case, the escape phase begins. [2]

The tumour escape can happen through different mechanisms, including reduced immune recognition (where the Cancer cells hide the proteins on the membrane that are used to help immune cells identify them as Cancerous), resistance to immune cells or creating a tumour microenvironment [4]. All these ‘abilities’ of immune cells can appear due to further mutations obtained in the equilibrium phase. The result is that the immune system cannot control the tumour's growth effectively, and the Cancer grows uncontrollably, becoming a life threat.

This was a simplified version of why Cancers appear. There are numerous process and molecules all taking part in the processes mentioned above and there are even more details to each of the processes. However, these were the basics.

In the end, Cancer appears spontaneously. We can only decrease the risks by avoiding carcinogens and making sure that our immune system works properly, as it is the key player in Cancer development.

References

1.Gutschner, T. and Diederichs, S. (2012). The hallmarks of cancer. RNA Biology, [online] 9(6), pp.703–719. doi:https://doi.org/10.4161/rna.20481.

‌2.Swann, J.B. and Smyth, M.J. (2007). Immune surveillance of tumors. Journal of Clinical Investigation, [online] 117(5), pp.1137–1146. doi:https://doi.org/10.1172/jci31405.

‌3.Beer, G. (2019). Why doesn’t the immune system attack cancer cells? Science surgery: [online] Cancer Research UK - Cancer News. Available at: https://news.cancerresearchuk.org/2019/02/28/science-surgery-why-doesnt-the-immune-system-attack-cancer-cells/?utm_source=chatgpt.com [Accessed 29 Dec. 2024].

4.Mittal, D., Gubin, M.M., Schreiber, R.D. and Smyth, M.J. (2014). New insights into cancer immunoediting and its three component phases—elimination, equilibrium and escape. Current Opinion in Immunology, 27, pp.16–25. doi:https://doi.org/10.1016/j.coi.2014.01.004.