Osteopontin Identified as Lead Marker of Colon Cancer Progression, Using Pooled Sample Expression Profiling

Background: New tumor markers and markers of tumor progression are needed for improved staging and for better assessment of treatment of many cancers. Gene expression profiling techniques offer the opportunity to discover such markers. We investigated the feasibility of sample pooling strategy in combination with a novel analysis algorithm to identify markers. Methods: Total RNA from human colon tumors (n = 60) of multiple stages (adenomas; cancers with modified Astler Collier stages B, C, and D; and liver metastases) were pooled within stages and compared with pooled normal mucosal specimens (n = 10) by using oligonucleotide expression arrays. Genes that showed consistent increases or decreases in their expression through tumor progression were identified. Northern blot analysis was used to validate the findings. All statistical tests were two-sided. Results: More than 300 candidate tumor markers and more than 100 markers of tumor progression were identified. Northern analysis of 11 candidate tumor markers confirmed the gene expression changes. The gene for the secreted integrin-binding protein osteopontin was most consistently differentially expressed in conjunction with tumor progression. Its potential as a progression marker was validated (Spearman's ρ = 0.903; P