Abstract: Methods for the distinctive identification and characterization of Cancer Giant Cells, which have a size of 15 microns or more (major axis), which express abnormally high amounts of telomerase, and/or which express syncytin and/or cancer associated antigens and Giant Cells associated antigens such as macrophage antigens which distinguish them from non-cancer Giant Cells. Use of Cancer Giant Cells as a liquid biopsy biomarker to determine the presence of cancer, early detection of cancer, early detection of cancer recurrence, determination of therapy and of treatment response. Use of the Cancer Giant Cells liquid biopsy biomarker for determining the risk of having cancer or cancer recurrence or of being at risk of developing cancer or cancer recurrence, and for treating the subject with personalized therapy against cancer to treat or prevent cancer or cancer recurrence. A kit for detecting Cancer Giant Cells and its use to detect cancer and cancer recurrence and manage cancer treatment is disclosed.