Multivariate analysis of serum tumor markers for diagnosis of skeletal metastases.

Serum tumor markers, including carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), carbohydrate antigen 15-3 (CA 15-3), carbohydrate antigen 19-9 (CA 19-9), cancer antigen 125 (CA 125), and tissue polypeptide antigen (TPA), were measured in 26 patients with skeletal metastases and 11 patients with primary malignant bone tumors. TPA, which was elevated in 16 patients (61.5%), was the most sensitive marker for detection of skeletal metastases. Combined measurement of these markers was useful in detecting skeletal metastases from primary lesions, although tumor markers had little organ specificity. In addition, skeletal metastases could be completely differentiated from primary lesions by the use of multivariate discriminant analysis of markers. The most and least powerful discriminating factors were AFP and CA 19-9, respectively. On multidimensional scaling, the distance between AFP and CEA was longest, with the other markers scattered between them. Expression of individual markers can not be linked to that of other markers.