A patient under goes chemotherapy for cancer. Chemotherapy aims to shrink or halt the growth of the primary cancer. It is called a systemic treatment in that it also aims to get rid of any cancer cells that might have spread to the rest of the body. Chemotherapy is effective because the drugs work against rapidly dividing cancer cells. Unfortunately the body has many different kinds of rapidly dividing cells which means the chemotherapy will affect them too – these are known as side effects.