A drug used alone or with other anticancer drugs to treat certain types of colorectal cancer that have spread to other parts of the body. It is used in patients whose cancer has not already been treated or whose cancer got worse after treatment with other anticancer drugs. It is also being studied in the treatment of other types of cancer. Panitumumab binds to a protein called epidermal growth factor receptor (EGFR), which is found on some normal cells and some types of cancer cells. Blocking this protein may help keep cancer cells from growing. Panitumumab is a type of monoclonal antibody. Also called ABX-EGF and Vectibix.