This document provides methods and materials for identifying biomarkers (e.g., peptide biomarkers) that can be used to identify a mammal as having a disease (e.g., cancer). This document also provides methods and materials for identifying and/or treating cancer. For example, this document provides methods and materials for using one or more peptide fragments derived from a peptidyl-prolyl cis-trans isomerase A (PPIA) polypeptide to identify a mammal as having cancer (e.g., ovarian cancer).