Forty-six patients who had been evaluated because of skeletal metastases of unknown origin, were reviewed. Twenty-six of the patients were referred to an orthopedic surgeon before confirmation of the metastases by biopsy; 20 others were referred to an oncology clinic after a diagnosis of bone metastases had been established. A simple diagnostic sequence consisting of a medical history, physical examination, routine laboratory studies, chest roentgenogram, technetium 99m phosphonate bone scintigram, and intravenous pyelogram identified the site of the primary tumor in 14 patients; 7 of the primaries were lung carcinomas, 4 were hypernephromas, 2 were breast carcinomas, and 1 was a prostate carcinoma. In two other patients, the histologic findings from the biopsy study were diagnostic; one had a thyroid carcinoma and one, a prostate carcinoma. Further extensive diagnostic workups revealed the site of origin in only four additional patients; two had hypernephromas which were discovered by computed axial tomography of the abdomen; one had an ovarian carcinoma and one had a hepatoma, both of which were found a t laporatomy. On the basis of this study, a simple diagnostic strategy is recommended for patients with histopathologically confirmed skeletal metastases of unknown origin: medical history, physical examination, routine laboratory studies, chest radiograph, and technetium 99m phosphonate bone scintigram, followed by computed axial tomographic examination of the abdomen and pelvis. In female patients, it may be judicious to use mam-mography. If this regimen fails to reveal the primary site, it is unlikely that it will be identified with further extensive diagnostic procedures. Cancer 58:1088-1095, 1986. OST SKELETAL MALIGNANCIES are found to be met-M astatic rather than primary tumors. In 3% to 4% of all patients with metastatic carcinomas, however, the site of the primary carcinoma is unknown.'-' In approximately 10% to 15% of these patients, skeletal metastases are the first lesions to be dete~ted.'.~,'.~ The primary location is not often identified despite extensive investigation , and only infrequently does the discovery of the primary tumor influence patient s u r ~ i v a I. ~ ~ ~ ~ ' ~ ~-' ~ In earlier studies, no effort had been made to separate patients with skeletal metastases from those who had metastases in lymph nodes, liver, lung, or other non-skeletal sites. Therefore, we retrospectively analyzed 46 patients who had been referred to our institution with skeletal rnetas-tases as the initial manifestation of a previously unknown carcinoma. We attempted to determine the success rate in locating the primary tumor site, to ascertain the prognosis , and to devise an optimal diagnostic strategy in such cases.
