Cancerous cells are quite different from normal cells. Normal cells have specific functions in the body and mature into distinct cell types but cancer cells do not have any specialized function in the body, they just continue to grow and divide indiscriminately.
They are also unable to receive signals from the body hence the reason why they do not fulfill a normal cell life cycle known as apoptosis. Apoptosis is the natural way through which the body rids itself of unwanted cells, allowing new ones to take their place.
So, for normal cells, it’s all programmed so that there are no unwanted cells but cancerous cells do not conform to this. Instead, they continue to grow and divide as they please and may even influence normal cells and blood vessels around a tumor to begin to feed it with nutrients and oxygen so that the tumor continues to grow bigger.
Cancerous cells may also invade the immune system, the system responsible for fighting off infections and ridding the body of foreign bodies. Normally, the immune system is built to be able to rid the body of abnormal cells but when cancerous cells invade the immune system, they are able to live in the body undetected and use the immune system to protect the tumor so that instead of the immune system fighting off the tumor, it begins to defend and protect it.
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