The etiology of diverse patient responses to a given pharmaceutical treatment has eluded science for decades. Only during the last 10-15 years has our understanding of the interplay between genetics and pharmaceuticals advanced to the point that personalized medicine may optimize therapies for each individual patient. The primary goals of personalized medicine are identifying individuals at risk of developing disease to better prevent disease in the healthy population, accurately monitoring each patient's response to therapy and predicting recurrence in order to pre-empt it. This review gives an explanation of biomarkers and addresses their role in the diagnosis and surveillance of various cancers. It also addresses the challenges of developing novel therapies utilizing newly discovered biomarkers.