Metastatic adeno or undifferentiated carcinoma from an unknown primary site--natural history and guidelines for identification of treatable subsets.

Two hundred and eighty-six patients presenting with metastatic adenocarcinoma or undifferentiated carcinoma whose primary site was not identified by clinical history, physical examination and chest radiograph have been studied. Median survival from presentation was 22 weeks. Factors independently predicting improved survival were lymph node presentations, good performance status and body weight loss of less than 10 per cent. In 88 (31 per cent) patients the primary tumour site was subsequently identified, in 58 (20 per cent) during life. Lung cancer was the most frequently identified primary tumour, and in only 32 (11 per cent) of the patients was a 'treatable' primary tumour (i.e. germ cell, breast, ovarian, prostate, thyroid cancer or lymphoma) identified. Among the treatable primary tumours were those in eight out of 16 female patients presenting with axillary metastases who were subsequently shown to have primary breast cancer and four of 13 females presenting with ascites who were found to have primary ovarian cancer. Prostatic cancer was confirmed in five out of 13 men with raised serum acid phosphatase. Of 22 patients with elevated serum alphafoetoprotein (AFP) or beta-human chorionic gonadotrophin levels (beta HCG) 18 had some features of the 'atypical teratoma syndrome'. Of the total of 32 patients with treatable tumour types, 29 (90 per cent) were identified during life. Median survival for patients with treatable tumour types identified during life was 104 weeks, compared with 22 weeks for the group as a whole. Retrospective immunocytochemical staining of the original biopsy showed that prostatic specific antigen and antibodies to beta HCG and AFP were diagnostically useful, but a series of organ site non-specific markers of histogenesis or cellular differentiation (carcinoembryonic antigen, secretory component for IgA, peanut lectin binding, epithelial membrane antigen and keratin) showed no significant correlations with identified primary sites, responsiveness to empirical chemotherapy or survival. Metastatic undifferentiated carcinoma or adenocarcinoma from an unknown primary site represents 6.5 per cent of all referrals to the medical oncology unit, Royal Prince Alfred Hospital, Sydney. We offer guidelines for the rapid identification of the limited number of primary sites for which effective and specific forms of systemic treatment are available.