Cancer represents a leading cause of death in the developed countries. The past 50 years have witnessed major progress in both laboratory medicine and clinical oncology that has translated into improved prognosis of cancer patients. From the humble beginnings as unrelated specialties, major advances in the understanding of molecular bases of cancer progression led to increased interactions between laboratory medicine and clinical (mostly medical) oncology. Laboratory medicine is now an integral part of the management of cancer patients. The many aspects of the role of laboratory medicine in clinical oncology include the determination of biomarkers that are used in establishing the diagnosis, predicting response to therapy or prognosis, study of the host response to tumor growth, detection of treatment toxicity and determining the concentrations of anticancer drugs.