Early in my regulatory medical writing career, I wrote several protocols in the cardiology therapeutic area. I was introduced to the cardiac biomarkers troponin I and N-terminal prohormone brain natriuretic peptide (NTproBNP), which are indicators of cardiac injury and cardiac dysfunction, respectively. Before that, I had done a lot of work in oncology, and I was accustomed to biomarkers such as HER2 that can be used to define a patient population for a given treatment.