Monoclonal antibodies are drugs that recognise and lock onto specific proteins (receptors) that are present in particular cancer cells.

Some cancer cells have parts known as epidermal growth factor receptors (EGFRs). When proteins in the body known as growth factors attach to these receptors, the cancer cell is stimulated to grow and divide. The monoclonal antibody cetuximab (Erbitux®) locks onto the EGFR, stopping growth factors from attaching, and so may prevent the cancer cell from growing and dividing. Before having cetuximab, doctors test whether the cancer cells have enough EGF receptors. Cetuximab is given as a drip (infusion) into a vein.

Another monoclonal antibody called bevacizumab (Avastin®), which works in a slightly different way to cetuximab, can also be used to treat advanced cancers of the colon and rectum that have not been controlled by other chemotherapy combinations. Bevacizumab works by preventing the tumour from developing a new blood supply, and so starve the cancer of oxygen and nutrients. Drugs that interfere with blood vessel growth in this way are called angiogenesis inhibitors or anti-angiogenics.

The National Institute for Health and Clinical Excellence (NICE), which advises doctors about treatment, currently does not recommend the routine use of either cetuximab or bevacizumab in the treatment of advanced (metastatic) bowel cancer. As a result it may not be possible to get either drug on the NHS. However, NICE recommends that people who are currently receiving bevacizumab or cetuximab should be able to continue the treatment – as long as their doctor thinks it is needed.

Some people can have an allergic reaction to monoclonal antibodies. This can make you have a flu-like reaction, a drop in blood pressure or feel sick. Other possible side effects include skin rashes and tiredness. With some monoclonal antibodies, the first dose is given slowly, over a number of hours. You may be given some other drugs first to make a reaction less likely.