The burden of the decisions related to cancer management is the reason why doctors are trying to use the best indicators to manage doubt and uncertainty, as well as to improve treatment targeting. These indicators are called tumor markers. They may assist in the diagnostic process and help in establishing the prognosis. They may be used for screening an asymptomatic disease, early detection of recurrent disease and mainly follow-up during cancer therapies. The better understanding of carcinogenesis coupled to technical improvements led to the discovery of new markers. They target cellular or genetic abnormalities and revisit classic cancer classification while some predict disease response to targeted therapies. This is the era of personalized oncology.