Question: How do people get cancer?

Isabel Pires answered on 12 Mar 2015:

Looking at the biology behind it, there are several ways in which cancers can start. Some of them even happen at the same time, or follow each other.

In some cases, cancers are are caused by defects or mutations in some genes important for making sure cells divide and grow normally. These genes are called tumour suppressors, because in their normal day-to-day job they stop any attempt of the cell to become tumour-like. When some damage to the DNA occur in a normal cell, these genes will be made into proteins that can tell the cell to repair that damage and stop dividing whilst this happens. If the damage is too much to handle, these proteins will trigger a death process, so that cell will die (and only that cell), to prevent the tissue being taken over by cells that might become a cancer.

In other cases, cancers can be caused by some other type of genes, called oncogenes, becoming too active. These genes can make cells grow faster, spread quicker, and survive better.

Finally, there are other things or factors that can allow cancers to develop, which are part of the environment where they are growing, such as the presence of inflammation that does not go away (like a wound that cannot heal), or there being low or no oxygen. These factors can change the way cells behave by changing the genes that are active and the proteins that are being made, including some that are involved in making cancer cells spread better, resist cell death, change the way they get their energy, etc.

Mutations in the DNA can be caused by normal day-to-day living (after all, we all breath oxygen and oxygen can be quite damaging to the DNA when it reacts with it!) and also during ageing, because our cells are not so able to repair the DNA. However, external causes can trigger cancer, such as smoking, being out in the sun for too long unprotected, or bad diet and no exercise.