[Cancer of unknown primary. Epidemiology and pathogenesis]

The term cancer of unknown primary (CUP) describes by definition epithelial malignancies for which no primary tumor can be found after primary diagnostics have been performed.

The CUP syndrome constitutes 2-3% of all fatal cases of malignancies in both men and women. The proportion of women has increased in parallel to the increase of tobacco consumption in women.

The most frequent origin appears to lie in the lungs or upper abdominal organs, while notable differences can be found between older autopsy findings and recent gene expression data with respect to identified primary tumors or tissue assignation. The fact that a primary tumor cannot be identified is probably based on various reasons: a complete regression of a primary tumor in isolated cases seems to be just as plausible as the misclassification of a primary tumor as a metastasis.

In combination with the fact that a primary tumor cannot be identified by autopsy in more than 20 % of cases, the important conclusion can be drawn that curative approaches seem appropriate for localized CUP cases.