Semmelweis Egyetem, I. Patológiai és Kísérleti Rákkutató Intézet, Budapest
SUMMARY – The effi cacy of the antitumor therapy is usually limited due to the resistance against the chemotherapy. One of the most important reason of the secunder resistance is the intratumoral heterogeneity, which is the consequence of the variety tumor phenotypes in the same tumor. Such clonal heterogeneity develops during the tumor growth or tumor therapy. The cancer stem cells (CSC), according to the concept, can determine the progression of the tumor, including metastatization, which probably the major enemy for clinical oncology. This activity of CSC, in tumors with epithelial origin, is supported by a change from epithelial to mesenchymal phenotype (epithelial-mesenchymal transition); but not entirely. The CSC phenotype is very similar to characteristic of the normal stem cells, as resistance, self-renewal etc. The mechanisms of these concepts is known only partially, but the technical advances contribute to the identifi cation of key genetic and epigenetic regulatory pathways. If such improvement becomes real, we can be much ahead both with markers and therapeutic targets.