Cancer stem cells and their role in metastasis.

Introduction: Cancer, next to cardiovascular diseases, remains the primary concern of modern medicine in developed countries. Despite the unprecedented progress in targeted therapies and personalised medicine, including immunotherapy and gene therapy, we are still unable to efficiently treat many malignancies. One of the major obstacles to treating cancer is its ability to metastasise. Hence, a better understanding of cancer biology with emphasis on the metastasis formation may hold the key to further ameliorating cancer treatment. Nowadays, there is a growing body of evidence for the common denominator of neoplasia, which seems to be universal - cancer stem cells which are being found in a growing number of cancers.

Material and methods: We conducted a Web of Science and Medline database search using the terms "cancer stem cells", "carcinogenesis", and "stem cells" in conjunction with "metastasis", without setting time limits.

Results: The existence of cancer stem cells was proven both in animal models and in humans. We know beyond doubt that cancer stem cells may be found in bladder cancer, breast cancer, and colon cancer, among others. The cancer stem cells in the aforementioned cancers may initiate tumour formation ex vivo and thus theoretically lead to tumour recurrence. Their role in the formation of metastases, however, is still under investigation.

Conclusions: Although their exact role is yet to be identified, it is now obvious that cancer stem cells give rise to primary mass in solid tumours and differentiated cancer cells in leukaemias. However, the role of cancer stem cells in metastasis is still obscure.