To evaluate the respective contributions of various investigations used to identify the primary tumor in a cohort of patients referred for diagnostic evaluation of one or more bone metastases.

A single-center retrospective study was conducted in a cohort of patients admitted between October 1990 and January 2000 for evaluation of one or more bone metastases with no known primary. All patients underwent radionuclide bone scanning, a chest radiograph, and an abdominal ultrasound scan. Computed tomography (CT) of the chest and abdomen, CT of the brain, and tumor marker assays were performed as clinically indicated. Using the final diagnosis as the reference standard, we evaluated the diagnostic usefulness of each investigation.

The 152 patients (104 men and 48 women) had a mean age of 63.5±12.5years. The primary was located in the lung in 37 patients, prostate in 26, breast or female genital tract in 24, urinary system in 11, gastrointestinal tract in 11, head and neck in 6, and other organs in 4. In 33 patients, no primary was identified. The extraskeletal metastases were located chiefly in the liver (20.4%), lung (17.1%), pleura (13.2%), and brain (7.2%). Bone biopsies were performed in 107 patients: 84 had a single bone biopsy, 16 had two bone biopsies, and 7 had three bone biopsies. The first bone biopsy was taken in the rheumatology department with or without fluoroscopic guidance in 62 patients, in the radiology department under CT guidance in 6 patients, and in the surgery department in 32 patients; this information was unavailable for the 7 remaining patients. The first bone biopsy was taken from the iliac bone in 48 patients, spine in 32, sacrum in 10, rib in 3, and other sites in 7. The histological biopsy findings indicated adenocarcinoma in 58 cases, epidermoid carcinoma in 28 cases, undifferentiated carcinoma in 2 cases, and other histological patterns in 9 cases. In 80 patients, another metastatic site was easier to access than the bone metastasis. Tumor marker assays were of limited value for determining the site of the primary, with the exception of prostate-specific antigen.

Bone biopsies performed by rheumatologists, generally under fluoroscopic guidance, usually indicate the site of the primary or at least the histological type. Tumor markers are often positive but are of limited usefulness for identifying the primary.