Understanding how cancer happens

What is cancer?

Cancer is a group of diseases that involve the unregulated growth of components of our bodies called cells. Almost everything in the body is composed of individual cells or is made by them. Cells are the units of life, and cancer can affect almost any type of cell. In cancer, cells grow and migrate throughout the body, affecting other tissues, until normal functions necessary for life, cannot be sustained anymore. Some of the most common organs affected are: the colon, breast, prostate, and lung.1

What is cancer and how it relates to tumors?

A tumor is an abnormal collection of cells, which are not necessarily harmful. Some of these can be harmful not because they are cancerous, but because of other reasons, such as, tumors that produce too much of a hormone.2 Cancer can be a tumor that has changed from being benign to malignant. Malignant tumors, proliferate excessively and invade the territory of other tissues.3

How cancer happens?

Our body is made mainly of individual cells that cooperate with each other to achieve the complex functions required for an organism.
Inside all of our cells, we have a molecule called DNA (short for deoxyribonucleic acid), which among other things, regulates the growth and reproduction of our individual cells.

DNA stores information about how everything should work in the body, but in some cases, the information it contains can be altered or removed. Damage to this molecule is the origin of cancer.4

This molecule is protected in an area of the cell called the nucleus, but many things can reach it here and cause damage to it. These things are known as mutagens, if they cause a change in the sequence of DNA, and if the change causes cancer, they can be classified as carcinogens.5

Normally, DNA in the nucleus is copied into another molecule called, RNA (ribonucleic acid). Molecules of RNA then leave the nucleus and enter a part of the cell called the cytoplasm. The information of RNA is used to generate many types of proteins. The normal functions of proteins include: acting as enzymes for the body, forming part of structures, acting as carriers, messaging, and in defense from invaders. In relevance for cancer, some of these proteins are very important because they can either promote cancer or block it, and if the DNA is damaged, the production or functioning of these cancer-related proteins, can in turn, be affected.6 The proteins that block cancer are known as tumor suppressors proteins, while the ones that promote it, are known as oncogene encoded proteins.7

Some tumor suppressor proteins can restrict or even kill a potentially cancerous cell; therefore, if these proteins are not doing their normal job, this can provide an opportunity for potentially cancerous cells, to progress in their path towards cancer.8 It is normal for some cells to mutate and go this way, but the tumor suppressor proteins provide ways to control this.9 Yet, if the tumor suppressor proteins are affected, the probability of cancer occurring are greater.10

Oncogene generated proteins can be codified by some segments of DNA called oncogenes.11 In a normal cell, there are only proto-oncogenes, but when damage to DNA occurs, these can turn into oncogenes.12 The proto-oncogenes are present for promoting normal growth of cells, but the oncogenes can promote an abnormally high rate of growth.13

Usually, it is a combination of mutations that lead to cancer.14 As cells accumulate more and more mutations, their growth and reproduction cannot be controlled effectively by the body, and this leads to harmful effects for the organism.15 Natural selection of resistant cells lead to their persistence and endurance to treatment.16


1. Rebecca L. Siegel, Kimberly D. Miller, and Ahmedin Jemal, “Cancer Statistics, 2020,” CA: A Cancer Journal for Clinicians 70, no. 1 (2020): 11, figure 1, https://doi.org/10.3322/caac.21590.

2. Joyce J Shin, Phillip Gorden, and
Steven K Libutti, “Insulinoma: Pathophysiology, localization and management,” abstract, Future oncology 6, no. 2 (2010): 229, https://doi.org/10.2217/fon.09.165.

3. Aisha Patel, “Benign vs Malignant Tumors,” JAMA Oncology 6, no. 9, 1488, https://doi.org/10.1001/jamaoncol.2020.2592.

4.Theodor Boveri, “Concerning the Origin of Malignant Tumours by Theodor Boveri. Translated and Annotated by Henry Harris,” Journal of Cell Science 121, no. Supplement 1 (2008): 1–84, https://doi.org/10.1242/jcs.025742.

5. Anthony JF Griffiths et al.,  “Relation between mutagens and carcinogens,” in An Introduction to Genetic Analysis, 7th ed. (New York: W. H. Freeman, 2000), https://www.ncbi.nlm.nih.gov/books/NBK21788/.

6. Harvey Lodish et al., “Proto-Oncogenes and Tumor-Suppressor Genes,” in Molecular Cell Biology, 4th ed. (New York: W. H. Freeman; 2000), sec. 24.2, https://www.ncbi.nlm.nih.gov/books/NBK21662/.








14. J. C. Fisher,  “Multiple-Mutation Theory of Carcinogenesis,” Nature 181, no. 4609 (1958): 651–52, https://doi.org/10.1038/181651b0.


16. Angelo Fortunato et at., “Natural Selection in Cancer Biology: From Molecular Snowflakes to Trait Hallmarks,” Cold Spring Harbor Perspectives in Medicine 7, no. 2, https://doi.org/10.1101/cshperspect.a029652.


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