For a cancer patient, almost all approaches regarding diagnossis, follow-up, prognosis and treatment rely on the phenotypic or genotypic features of the cancer cells. Biopsy should be definitely performed. One of the main characteristics of malign neoplasms is the ability of metastasis. Cancer cells from a primary focus get into circulation and are transferred to possible metastatic sites via blood. Cells that are in transfer in blood, circulating tumor cells (CTC), got much attention by researchers as a replacement of biopsy due to the fact that they have diagnostic, predictive and prognostic features. Several methods for detecting CTC have been developed till today since 90s. Cells can be purified either by their physical properties or their specific antigens on their cell membrane (i.e. EpCAM). Studies showed the correlation between the number of detected CTC and progression free survival and/or overall survival time in breast, colorectal and prostate cancers, as well as some other cancer types. CTC is a reliable source for patient selection for targeted therapy, by detecting Her2 expression for breast cancer or EGFR mutation for lung cancer. Since PSA has a low specificity and it gives limited information about prostate cancer, CTCs are thought to be a promising tool for prostate cancer and many studies were conducted on the role of CTCs in prostate cancer. Studies have shown that CTCs have prognostic impact in prostate cancer and also that they may be utilized as a source to detect drug resistance of cancer cells. Although CTCs have a great potential in their clinical use, obtaining them is still highly laborious and the test requires a high volume of blood. Moreover, the time of the test and how many repetitions of tests required for each patient are still unclear. But these issues expected to be clarified in the light of future studies.

Keywords: Circulating tumor cells, prostate cancer, prognosis