Protein biomarkers. Proteins are particularly useful molecules to use as biomarkers as they are often the effectors of diseases and the targets of therapeutic treatments. Using panels of protein biomarkers, healthcare experts can perform accurate disease diagnosis through convenient non-invasive testing. In cancer research, molecular biomarkers refer to substances that are indicative of the presence of cancer in the body. Biomarkers include genes and genetic variations, differences in messenger RNA (mRNA) and/or protein expression, posttranslational modifications of proteins, and metabolite levels.