when extra cells do not belong where they grow, they cause cancer.
Step-by-step explanation:
When there is overgrowth of cells, that is they grow and multiply in an uncontrolled manner, they result in cancer.
In cancer, cells spread to any body part where they don't belong.
It is a normal function of a cell to grow and then divide and after that it dies. But, when a cell starts growing and dividing and then again growing and dividing kind of it becomes immortal, then it becomes a cancerous cell.
The exact reason of cancer is yet to be know. But still after much research, scientists and researchers have some idea that cancer may be as a result of some genetic factor or due to some environmental change.
Still, research is going on to know it better so that the cause can be known and thus, scientists and researchers can work to prevent its occurrence.
Now a days, it is possible to cure cancer. In most cases, early deduction helps in starting early treatment which results in complete cure of the disease.