How Herceptin Works

Cancer cells are cells that grow in an uncontrolled fashion. Herceptin stops or slows the growth of certain breast cancer cells by blocking the chemical signals they need to grow.

Chromosomes inside every cell contain genes, which regulate the cell's growth, rest, and repair. The genes do this by ordering the production of special proteins that tell the cells what to do. Each protein sets off a step in a chain of reactions, resulting in the desired cell activity—growth, rest, or repair.

Sometimes, if there's a problem with a gene or chromosome, the chain of reactions may not work properly. For example, when there's too much of the HER2 gene, it orders an excess production of protein receptors on the surface of cancer cells, called HER2 receptors. Receptors are like ears, or antennae, on the surface of each cell that receive the signal to grow.

When HER2 receptors are turned on and get excited, they tell the cells to grow. With too many receptors, breast cancer cells pick up too many growth signals and start growing too much and too fast. One way to slow down or stop the growth of the cancer cells is to block the receptors so they don't pick up as many growth signals. That's what Herceptin does.

Herceptin is a special antibody protein medication that attaches itself to the HER2 receptors on the cancer cells and blocks them from receiving growth signals. Herceptin can also alert the immune system to destroy the cancer cells it attaches to.

Because it doesn't usually attach to other types of proteins, Herceptin rarely affects other cells in the body. This means that it causes few serious side effects.