Epidemiology of unknown primary tumours; incidence and population-based survival of 1285 patients in Southeast Netherlands, 1984–1992

Patients with an unknown primary tumour (UPT) represent 5–10% of all new cancer patients. Data on survival and prognostic factors of UPTs are based on selected patient series from specialised institutions. Population-based data on incidence, histology and determinants of survival for patients with UPT are not available. All patients diagnosed with UPT between 1984 and 1992 and entered in the population-based Eindhoven Cancer Registry for Southeast Netherlands were included. Follow-up of vital status is complete up to 1999. 1285 patients were registered. In 1024 patients, the diagnosis was confirmed histopathologically: 479 (47%) had adenocarcinoma, 453 (44%) poorly differentiated carcinoma (PDC) or adenocarcinoma (PDA), 76 (7%) squamous cell carcinoma and 16 patients (2%) had an undifferentiated malignant neoplasm. In 26% of these patients with UPT, the tumour was already widely disseminated at presentation. The majority of patients (67%) received only supportive treatment. The median survival was 11 weeks and only 15% were still alive 1 year after diagnosis. Favourable subgroups comprised young patients and patients with metastases localised in lymph nodes. In 261 cases, the diagnosis was made clinically. These patients were evaluated separately. They were older than the biopsy-confirmed patients, received less cancer therapy and their prognosis was even worse (median survival of 7 weeks). In a comparison with data from a tertiary referral centre in the United States of America (USA), our patients were older, received less therapy and had a poorer prognosis. Demographics of our favourable subgroup resembled the patients from the American study. The differences were most likely caused by the differences in the patient populations. In conclusion, we have demonstrated in a population-based study that the prognosis for patients with UPT is more unfavourable than suggested in most clinical studies.