Normal Cell

When the epidermal growth factor (EGF) binds to the EGF receptor on the surface of a cell, it initiates a growth signalling pathway. This pathway turns on a gene associated with cell division, which causes the cell to divide into two new cells.

Cancer Cell

Many cancer cells have too many EGF receptors on their surface. Binding of EGF to these receptors results in excessive signalling along growth pathways, leading to unregulated cell division and tumor growth.

Cancer Cell plus Drug

Many cancer drugs currently under development work by targeting the EGF receptor. Some of these drugs target the signalling portion of the receptor inside the cell. Drug binding prevents the receptor from activating the growth pathway. Administering only enough drug to disable some EGF receptors on a cancer cell while leaving a few active will hopefully restore normal signalling and cell division, thus inhibiting tumor growth.