[Malignant tumors of unknown origin].

Cancers of unknown origin form a specific clinical entity. The diagnostic procedure has to be guided by the therapeutical possibilities and requires a biopsy. Immunohistology, electron microscopy and cytogenetics are informative for carcinomas and poorly differentiated adenocarcinomas. The clinical status and the histology allow the definition of groups of patients who can benefit from a specific therapy and have a better prognosis. For the other patients, the prognosis is severe and there is no efficient therapy available. Such tumors are usually characterized by a very aggressive behaviour.