[Pathohistology and molecular genetic diagnostics in CUP syndrome]

Patients with cancers of unknown primary (CUP syndrome) represent a relatively large group of cancer patients (5-10%) in whom the histomorphological diagnosis is made from tissue from the metastasis, and the site of the primary tumour remains unclear. The incidence is variable, depending on the definition used and the intensity of the search for a primary tumour. From a biological and prognostic point of view, it is helpful to distinguish eight clinical entities of the CUP syndrome; four of these entities can be subdivided histologically. Histopathologic diagnosis should be performed using a diagnostic algorithm based on the HE morphology and supplemented by immunohistochemistry. With the use of a broad spectrum of immunohistochemical markers, many tumour entities can be diagnosed, so in most cases molecular genetic investigations are not necessary.