Unknown primary adenocarcinoma: incidence of overinvestigation and natural history.

Out of 1300 patients referred to a medical oncology unit, there were 87 with metastatic cancer in whom a primary tumour site was not evident from the history and after physical examination and chest radiography had been carried out. An analysis of the investigations performed in these patients and their results showed that in only eight of the 87 patients did non-surgical investigations at presentation determine the primary site. In two patients it was identified by diagnostic laparotomy, and in a further 13 clinical follow-up led to recognition of the primary tumour site before death. Few investigations should be performed in patients in whom the primary site is known since they have a low yield, and in our population identifying the primary tumour did not improve the outcome or alter management. Treatable tumours should be excluded, and this may be done in most cases by simple blood tests, particularly those measuring acid phosphatase activity and other tumour markers.