CA19-9 is a biomarker often used in pancreatic cancer diagnosis; it measures serum CA19-9 levels in the blood which corresponds to cancer status and even staging. It is used clinically but not as a screening biomarker as it doesn’t have the specificity needed to make it cost-effective in a screening programme. It can be used before and after treatment as it can help in choosing a treatment plan. It is used to see if this treatment is working, so it works as a predictive and prognostic biomarker as well. It’s recently been used alongside tumour marker genes to improve its sensitivity and specificity.