panitumumab
Meaning of panitumumab: A laboratory-made antibody that plugs a growth switch on tumor cells, but only helps when one particular gene is unaltered.
Definition of panitumumab
Panitumumab is a treatment for advanced bowel cancer given by infusion. It is a fully human monoclonal antibody that attaches to the epidermal growth factor receptor, a protein on the cell surface that signals the cell to divide. By occupying the receptor it blocks the natural signal, slowing growth of tumors that depend on it.
How does it work?
Epidermal growth factor normally binds a receptor on the outside of a cell and starts a chain of messages that ends in cell division. Many bowel cancers rely on this route. Panitumumab binds the same receptor and covers the site where the natural signal would attach. Nothing is switched on, and the relay inside the cell stays quiet. The antibody is too large to enter the cell, so all of its effect happens at the surface.
Why does gene testing come first?
| RAS gene status | What the pathway does | Effect of the drug |
|---|---|---|
| Unaltered | Signal depends on the receptor | Blocking the receptor stops it |
| Mutated | Signal is switched on further downstream | Blocking the receptor changes nothing |
RAS proteins sit inside the cell, below the receptor in the same relay. A mutation locks them in the on position, so the message continues regardless of what happens at the surface. Testing the tumor for these mutations is done before treatment, because the drug offers no benefit when they are present and still carries its side effects.
What is distinctive about it?
It is a fully human monoclonal antibody, produced in genetically modified mice engineered to carry human antibody genes, rather than a mouse antibody adapted afterward. That reduces the chance of the immune system reacting against the drug itself. Its most characteristic side effect is a rash resembling acne over the face and upper body, which follows directly from the fact that skin cells also use this receptor. Low blood magnesium develops with continued treatment, because the same receptor is involved in magnesium handling in the kidney.
Also known as
Used in a sentence
Panitumumab was started after testing confirmed the tumor was RAS wild type.
Good to know
Tumors carrying a RAS mutation do not respond to panitumumab, because the growth signal continues below the level of the receptor the drug blocks.