Aim: Until recently, peritoneal metastases (PM) were regarded as an untreatable condition, regardless of the organ of origin. Currently, promising treatment options are available for selected patients with PM from colorectal, appendiceal, ovarian or gastric carcinoma. The aim of this study was to investigate the incidence, treatment and survival of patients presenting with PM in whom the origin of PM remains unknown. Methods: Data from patients diagnosed with PM of unknown origin during 1984-2010 were extracted from the Eindhoven Cancer Registry. European age-standardised incidence rates were calculated and data on treatment and survival were analysed. Results: In total 1051 patients were diagnosed with PM of unknown origin. In 606 patients (58%) the peritoneum was the only site of metastasis, and 445 patients also had other metastases. Chemotherapy usage has increased from 8% in the earliest period to 16% in most recent years (p = .016). Median survival was extremely poor with only 42 days (95% confidence interval (CI) 39-47 days) and did not change over time. Median survival of patients not receiving chemotherapy was significantly worse than of those receiving chemotherapy (36 versus 218 days, p < .0001). Conclusion: The prognosis of PM of unknown origin is extremely poor and did not improve over time. Given the recent progress that has been achieved in selected patients presenting with PM, maximum efforts should be undertaken in order to diagnose the origin of PM as accurately as possible. Potentially effective treatment strategies should be further explored for patients in whom the organ of origin remains unknown.

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Keywords Incidence, Peritoneal metastases, Prognosis, Treatment, Unknown primary neoplasm
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Journal European Journal of Cancer
Thomassen, I, Verhoeven, R.H.A, van Gestel, Y.R.B.M, van de Wouw, A.J, Lemmens, V.E.P.P, & de Hingh, I.H.J.T. (2014). Population-based incidence, treatment and survival of patients with peritoneal metastases of unknown origin. European Journal of Cancer, 50(1), 50–56. doi:10.1016/j.ejca.2013.08.009