The term originates from the Greek onkos ( Î Î 1\/2 Î Î Ï ) , meaning bulk , mass , or tumor ; and the suffix - ology , meaning `` study of . '' Oncology ( from the Ancient Greek onkos ( á 1\/2 Î Î Î Ï ) , meaning bulk , mass , or tumor , and the suffix - logy ( - Î '' Î Î Î Î ) , meaning `` study of '' ) is a branch of medicine that deals with tumors ( cancer ) .