Understanding how real-world outcome variables are developed informs their applicability to a variety of use-cases in oncology care and research. We need to ensure these outcome variables are of high-quality in order to have high confidence in the conclusions drawn from analyses of the resulting endpoints. Flatiron developed a composite mortality variable because a complete, timely single source of real-world death data does not exist. Our mortality variable is a combination of structured data from the EHR, unstructured documents (such as end of treatment notes or condolence letters), Social Security Death Index (SSDI) data, and obituary data.