ABSTRACT
Non-spine bone metastasis accounts for approximately 20% of all skeletal metastases, but little data have been published that focused on bone metastasis to the pelvis and extremities as an initial manifestation of cancer. We determined 1) clinicopathologic characteristics of patients who presented with non-spine bone metastasis of unknown primary malignancy, and 2) process by which the diagnosis of primary cancer was made. We retrospectively reviewed 84 patients with bone metastasis of unknown primary cancer site at the time of presentation. The study population consisted of 56 men and 28 women, with a mean age of 59.1 yr (17.5-85.6 yr). The average follow-up period was 20.8 months (1-120 mo). Primary cancer site was identified in 79 patients (94.0%), and was determined to be the lung (46.4%), kidney (13.1%), liver (9.5%), thyroid (8.3%), and prostate (4.8%). Five-year overall survival rate was 28.0%. Multiple bone metastases, distant organ metastasis, and multiple bone with organ metastases were the significant prognostic factors in univariate analysis. Multiple bone metastases remained significant after multivariate analysis (P = 0.008). Lung cancer is the most common site of primary cancer, and patients with multiple bone metastases have a poor prognosis, possibly due to disseminated cancer and a greater tumor burden.