3 GENES that are ABNORMAL in a CANCER CELL

There are 3 different types of Genes that are important in making a cell cancerous:

Healthy cells follow a life cycle of growth, division and death.   Like leaves on a tree, old cells die off and are replaced by an equal number of healthy cells.  Cancer develops when old cells refuse to die, but keep growing, dividing, and building up in one place – creating a TUMOR.  (breastcancer.about.com)
(the Truth About Cancer / Facts About Cancer)

Genes that encourage the cell to multiply       (ONCOGENES)

     Some genes encourage cells to multiply or 'double'. Normally, in adults, this would not happen very often. Cells would only multiply to repair damage, for example after a wound or operation.  BUT if these genes become abnormal, they tell the cell to multiply all the time.

(the Truth About Cancer / Facts About Cancer)

Genes that stop the cell multiplying       (TUMOUR SUPPRESOR GENES)

     Some genes are in the cell specifically to stop the cell doubling. If one of these 'tumour suppressor genes' becomes damaged and stops working, then the cell may carry on and on multiplying. In other words, it becomes immortal, which is one of the properties of a cancer cell.

(the Truth About Cancer / Facts About Cancer)

Genes that repair other damaged genes       (DNA REPAIR GENES)    

These genes normally repair any damage to the DNA that makes up the cell's genes. If these DNA repair genes are damaged, then other mutations are not repaired and the cell can copy the mutations into its daughter cells. These genes have been found to be damaged in some human cancers, including bowel cancer. (cancerhelp.org.uk)