Abstract: The invention relates to a method for the classification of cancer using a specific multi-class tumor classifier comprising specific sets of genes for the interpretation of expression data obtained from tumor samples. More specifically, the method of the present invention provides an accurate, reproducible, robust, objective and easy to perform method for determining the primary site of a Cancer of Unknown Primary site (CUP). For this purpose, the method provides that a classifier parameter is determined by comparing an expression profile of a tumor sample with a template profile representative for a particular primary site of a cancer.