Familial risks in cancer of unknown primary: tracking the primary sites.
PURPOSE Cancer of unknown primary (CUP) is diagnosed at the metastatic stage, and despite extensive diagnostic work-up, the primary tumor often remains unidentified. No data are available on familial clustering of CUP. We hypothesize that familial clustering of CUP with other cancers may be informative of the primary sites. PATIENTS AND METHODS A total of 35,168 patients with CUP were identified i