Tumor markers are substances used in oncology in order to obtain information about a particular malignant process. Their source is represented by the cancer cells or by the host, which produces them in the presence of tumor. They can be found in the blood, urine or body tissues, but their levels can be increased also by other causes than malignancies. Tumor markers can be used for many purposes such as screening, diagnosis orientation, estimating prognosis, predicting the response to treatment and a possible severe toxicity associated to treatment, detecting recurrences and monitoring treatment in late stage disease