Proteomes of patients suffering from diseases are being studied to understand the genetic basis of diseases. The most prominent set of diseases being studied with proteopmic approaches is cancer. Proteomic ptapproaches are being used to improve screening and early detection of cancer, which is achieved by identifying proteins whose expression is affected by the disease process.
An individual protein that indicates disease is called a biomarker, whereas a set of proteins with altered expression levels is called a protein signature . For a biomarker or protein signature to be useful as a candidate for early screening and detection of a cancer, it must be secreted in body fluids (e.g. sweat, blood, or urine) such that large-scale screenings can be performed in a non-invasive fashion. The current problem with using biomarkers for the early detection of cancer is the high rate of false-negative results. A false-negative is an incorrect test result that should have been positive. In other words, many cases of.. cancer go undetected, which makes biomarkers unreliable. Some examples of protein biomarkers used in cancer detection are CA-125 for ovarian cancer and PSA for prostate cancer. Protein signatures may be more reliable than biomarkers to detect cancer cells.