How does Cancer Develop?

A cell forms the part of cancer. A normal cell becomes abnormal or cancerous when it loses important control systems i.e. some significant genes in a cell are either destroyed or missing. This is called mutation.
Development of a cancer takes long time that is why most types of cancer are more common among older people. So years before your doctor could actually detect cancer, cancerous cells would have started multiplying themselves.
A cell can becomes cancerous if any of the following types of genes are missing or become abnormal.

- Oncogenes:
Normally, cells do not multiply all the time unless you are recuperating from a wound or a surgery. If these genes encourage abnormal multiplification of cells it can cause cancer i.e. cancerous cells too would get doubled.

- Tumor suppressor genes:
If genes, which prevents cell from doubling, are destroyed or stop working then cell may start multiplying abnormally. As a result cancerous cells too would start reproducing itself.
P53 is a best example of such types of genes.

- Genes that correct the damaged:
Normally, cells do not multiply all the time unless you are recuperating from a wound or a surgery. If these genes encourage abnormal multiplification of cells it can cause cancer i.e. cancerous cells too would get doubled.