Update on the diagnosis of cancer of unknown primary (CUP) origin.

The cancer of unknown primary (CUP) concept encompasses a heterogeneous group of cancers that are difficult to diagnose and that show diverse clinical and histopathological features. Currently, CUP is the fifth most frequent cancer diagnosis in women and the eighth in men. The ongoing development of new therapies specific to the various cancer types makes mandatory the identification of the primary tumour in CUP patients, so that they may benefit from advances in therapy and improvements in prognosis. Molecular detection techniques provide very useful tools in the prediction of primary tumour types and must be used together with clinical, histopathological and IHC diagnostic techniques. Steady collaboration and fluid communication between oncologists and pathologists is of the utmost importance for the correct interpretation of tests and the personalised approach required by each individual case. Work in multidisciplinary teams will result in significant changes in the diagnosis and treatment of these patients.