Additionally, seven COS development studies [21, 22, 26, 28–31] reported details on “how” to measure the outcomes proposed (i.e., the recommended OMIs, outcome measurement timing and outcome measurement sources), making it possible to classify data sources for outcome measurement into the following classes: (1) clinical data (e.g., prostate-specific antigen levels; 4 studies); (2) administrative data (i.e., death certificate; 3 studies); (3) PROMs (e.g., Expanded Prostate Cancer Index Composite (EPIC-26); 7 studies). Here, KLK3 is linked to prostate carcinoma.