Proteins called receptors live on the surface of cells. When a protein called a ligand binds to the receptor outside the cell, the receptor transmits the signal to the inside of the cell. This results in normal cell division and growth. Mutations in these receptors can cause this growth signal to be constantly “on” and lead to uncontrolled cell growth. Sometimes mutations occur in one of the signaling proteins inside the cell also causing constantly “on” growth. In either case, uncontrolled cell growth may result in the development of cancer.
How Targeted Therapies work:
Traditional cancer treatments like chemotherapy and radiation work by killing all rapidly dividing cells. Because some of our normal cells divide rapidly too, these treatments kill many normal cells in addition to killing cancer cells. This results in side effects like nausea, vomiting, diarrhea, hair loss, and low blood counts.
Targeted therapies work by targeting the parts of cancer cells that are different from normal cells: a mutated receptor or mutated signaling protein. Ideally, targeted therapies block the growth signal in cancer cells much more than in normal cells, making them more effective therapies with fewer side effects. However, most current targeted therapies do cause significant side effects.
Targeted therapies can block transmission of the growth signal at multiple points, as shown in the figures below: