[Cancer of unknown origin: diagnostic and therapeutic yield]

Patients with carcinoma of unknown origin represents at least 5% on the total neoplastic patients. A review of the main metastatic locations and the different histological types has been done; giving special attention to the most frequent primitive neoplasms. Diagnostic yield in this type of cancer is emphasized, since many times, it is advisable to limit the number of explorations directed to find the primary tumor, as they decrease patient quality of life while no profit is obtained from the knowledge of the primary tumor, for most of the patients. However, this must not drive us to the opposite end: diagnostic and therapeutic nihilism. We have to rule out, in a reasonable way, certain types of tumors which have an useful treatment even in advanced phases (oat all carcinoma, germinal neoplasms, lymphomas).