Pooling of case specimens to create standard serum sets for screening cancer biomarkers

Multiple identical sets of sera from cancer cases and controls would facilitate standardized testing of biomarkers. We describe the creation and use of standard serum sets developed from healthy donors and pooled sera from ovarian, breast, and endometrial cancer cases.

Two hundred seventy-five 0.3-mL aliquots of sera were created for each of the 95 healthy women, and residual serum was pooled to create 275 identical sets of 20 0.3-mL aliquots. Aliquots (1.0-1.5 mL) from 441 women were combined to create 12 breast and pelvic disease pools with at least 115 0.3-mL aliquots. Sets were assembled to contain aliquots from individual controls, replicates, and disease pools. Cancer antigens (CA), CA 125, CA 19.9, and CA 15.3, and carcinoembryonic antigen were measured in one set and in 217 women comprising six of the pelvic disease pools. Use of a set was illustrated for mesothelin (soluble mesothelin-related protein). Statistical output included concentration differences between pooled cases and controls (z values for single analytes; Mahalanobis distances for pairs), correlation between z values and sensitivities, coefficient of variations, and standardized biases.

Marker concentrations in the six pelvic disease pools were generally within 0.25 SD of the actual average, and z values correlated well with sensitivities. CA 125 remains the best single marker for nonmucinous ovarian cancer, complemented by CA 15.3 or soluble mesothelin-related protein. There is no comparable breast cancer biomarker among the current analytes tested.

The potential value of standard serum sets for initial assessment of candidate biomarkers is illustrated. Sets are now available through the Early Detection Research Network to evaluate biomarkers for women's cancers.