This document describes two studies that used online advertising systems to screen for cancer. The studies targeted ads related to cancer symptoms to individuals, who could then complete validated questionnaires. Questionnaire scores were correlated with past search queries to predict suspected cancer risk. The advertising systems learned to better identify potential cases. The second study improved targeting and found conversion rates of 11% for breast cancer, 9% for colon cancer, and 9% for lung cancer. The approach shows potential for early cancer screening but requires more validation and assessment.