Malignancies are considered as leading cause of death in parallel to cardio- and cerebrovascular diseases and their incidence is still growing from year to year. Early detection and monitoring of cancers after complex therapeutic interventions are essential for the survival of patients. In these aspects, beside radiological investigations, some lab tests play a key role, namely the tumor markers. These mostly protein-based mediators are produced in a large quantity by either cancer cells or the human body itself in response to the development of tumor. Measurement of tumor markers is usually assessed in serum samples, however, to locally detect an early malignant event, other body fluids, such as ascites, cerebrospinal fluid, or pleural effusion sample can also be analyzed. Due to the potential effects of other non-malignant conditions on the serum level of a tumor marker, the entire clinical status of investigated person needs to be considered for the correct interpretation of these results. In this review article, we summarized some important characteristics of the most widely used tumor markers.