How do we get cancerous cells?

The current theory of cancer is "one mutation, one cancer". According to this theory, a dividing cell in your body acquires a genetic mutation that somehow disrupts the normal control mechanisms. This mutated cell then continues to grow and divide. If the immune system doesn't destroy the mutated cell, and the cell is able to maintain nutrient flow into itself, it will eventually show up as a cancerous mass.

However, new research is unveiling just how complicated the development of cancer is. For instance, as the mutated cells keep dividing, they keep acquiring new mutations which can significantly change the behavior of the overall tumor. Also, sometimes just one mutation is not sufficient to cause a cell to become cancerous - in some cancers it appears there have to be a series of specific mutations before the cells start to exhibit cancerous properties.