Concordant release of glycolysis proteins into the plasma preceding a diagnosis of ER+ breast cancer

Abstract

Although the identification of peripheral blood biomarkers would enhance early detection strategies for breast cancer, the discovery of protein markers has been challenging. In this study, we sought to identify coordinated changes in plasma proteins associated with breast cancer based on large-scale quantitative mass spectrometry. We analyzed plasma samples collected up to 74 weeks before diagnosis from 420 estrogen receptor (ER)(+) cases and matched controls enrolled in the Women's Health Initiative cohort. A gene set enrichment analysis was applied to 467 quantified proteins, linking their corresponding genes to particular biologic pathways. On the basis of differences in the concentration of individual proteins, glycolysis pathway proteins exhibited a statistically significant difference between cases and controls. In particular, the enrichment was observed among cases in which blood was drawn closer to diagnosis (effect size for the 0-38 weeks prediagnostic group, 1.91; P, 8.3E-05). Analysis of plasmas collected at the time of diagnosis from an independent set of cases and controls confirmed upregulated levels of glycolysis proteins among cases relative to controls. Together, our findings indicate that the concomitant release of glycolysis proteins into the plasma is a pathophysiologic event that precedes a diagnosis of ER(+) breast cancer.

Figure 1. Quantified proteins in the glycolytic pathways

Color representation consists of red (increased levels), green (decreased levels) and yellow (no significant quantitative change) based on log2 ratios for the 0–38 week pre-diagnostic samples relative to matched controls.

Figure 2. Extensive peptide coverage for glycolysis proteins

Representative data for the identification of three glycolysis proteins, ALDOA, ENO1 and GAPDH, in a case control experiment illustrate the extent of coverage achieved in the identification of glycolysis proteins in plasma by mass spectrometry in this study. For each protein, the peptides identified are displayed below the predicted tryptic peptides. Orange indicates cysteine containing peptides used for determination of case/control ratios.

Figure 3. Gene set enrichment analysis in relation to time to diagnosis

The x-axis represents the rank of each protein's log2 ratio in descending order while the y-axis is the proportion of proteins represented in the gene set for each rank as utilized for gene set enrichment scores (6) which are normalized such that cumulative score is zero. The area under the curve (AUC) serves as a measure of how the protein ratios in one gene set are distributed among all proteins measured.