Site-specific survival rates for cancer of unknown primary according to location of metastases

Cancer of unknown primary (CUP) is diagnosed at the metastatic stage and despite extensive diagnostic work-up the primary tumor often remains unidentified. Limited population-based survival data are available for metastatic location and none are available that link the location with the cause of death, which might give clues about the tissue-of-origin. A total of 9,306 CUP patients with extranodal metastases of adenocarcinoma and undifferentiated histology were identified from the Swedish Cancer Registry. Hazard ratios (HRs), mean survival times and Kaplan-Meier survival curves were provided according to CUP location at diagnosis and cause of death. The median survival was shortest (2 months) for patients with liver and longest (5 months) for those with nervous system metastases. Lung cancer was the most common cause of death in patients with CUP metastasis in the respiratory system, nervous system, bone and skin, with a median survival of 3 months. Patients with peritoneal/retroperitoneal and pelvical metastasis died not only of ovarian cancer, with a favorable median survival of 8 months, but also of pancreatic and colorectal cancers. Patients with pancreatic, liver, biliary and colorectal cancers with liver metastasis succumbed quickly. The data show that the location of metastases predicts site-specific cancer deaths which in turn may point to the hidden primary tumor. The results should facilitate the management of CUP in proposing that the diagnostic arsenal should target the lungs when metastases are diagnosed in the respiratory or nervous system, bone or skin; ovarian tumors should be suspected after diagnosis of pelvical metastases. What's new? Cancer of unknown primary site (CUP) carries a high fatality rate and often is diagnosed at the metastatic stage, though there is little data available concerning relationships between survival and metastatic location. In this nation-wide study in Sweden, analysis of survival data for 9,306 CUP patients revealed that metastasis location is predictive of site-specific cancer deaths. For instance, patients with metastases diagnosed in the respiratory or nervous system or in the bone or skin frequently died of lung cancer. The findings may help with tissue-of-origin identification in CUP patients and thereby improve diagnosis and treatment.