In this post I will focus on some of the mechanisms that turn normal cells into cancer cells and why they are bad for us.
As you might already know cells can divide, one cell divides into two cells, two cells into four cells etc. Every time a cell divides, all its contents are copied so that the descendant cells have the same content as the parent cell. Control systems makes sure that the cell only divides when needed and that every step of cell division goes smoothly. If there is an error (e.g. DNA is not copied properly) cell division pauses so that the error can be repaired before it continues. If not repaired, the cell activates a self destruction program to prevent the formation of defect cells that could develop into cancer cells. After every cell division, the ends of the chromosomes (telomeres) get shorter. Once the telomeres become too short, the cells die. This is a safety mechanism to prevent cells to grow and divide indefinitely, which is a hallmark of cancer cells.
A normal cell does not turn into a cancer cell overnight. It’s a process that can take decades. During this process the behavior of the cell gradually changes as a result of errors (mutations) in the genes controlling cell growth and division. The changes includes for example the ability of the cell to keep growing without oxygen or having the ability to put back pieces of the telomeres after each round of cell division. These changes gives cancer cells a growth advantage over normal cells by being able to survive and divide in circumstances where normal cells would die. In short, cancer cells escapes death and becomes immortal. Even though there is a system that repairs mutations (and other errors), mutations can still slip through the system (spontaneous mutations) and the gradual accumulation of these mutations turns a normal cell into a cancer cell.
In addition to spontaneous mutations, external factors such as chemicals, radiation and viruses can also cause mutations. X-rays for example can cause pieces of DNA to break off or switch places with each other (DNA rearrangement), thus making the information in the DNA incorrect. Viruses such as the human papilloma virus on the other hand cause mutations by inserting its own DNA into the DNA of the cell it has infected. Insertion of viral DNA also results in that the host cell begins to produce virus particles that can infect other cells.
So why are cancer cells bad for us? Does it really matter if cells continuously divide? Cancer cells that continuously divide eventually form a lump of tissue called a tumor. Tumors can block blood vessels disrupting the flow of the blood or press against a nerve. Cancer cells can also invade and grow into organs rendering it dysfunctional. Cancer cells also releases hormones that negatively affect the normal function of the organs. In worst-case scenario, cancer cells from a tumor can detach and spread to another region of the body to form a new tumor in a process known as metastasis. Metastatic cancers are very difficult to treat.
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