A circulating tumor cell (CTC) refers to a type of a cell that has been shed from a primary tumor into the lymphatic system or the vascular system, and is carried all over the body through blood circulation. CTCs have the ability to extravasate and become a source for the creation of new tumors in distant organs. The identification and analysis of CTC can aid in early patient prognoses and deciding suitable personalized therapy. The detection of CTCs using liquid biopsy has a number of advantages over conventional tissue biopsies. Liquid biopsies are non-invasive and can be used multiple times. They also provide valuable information about metastatic risk, disease progression and treatment success. Analysis of blood samples from cancer patients has an increased possibility of CTC detection as the disease progresses. This book unravels the recent studies on circulating tumor cells in cancer. It presents researches and studies performed by experts across the globe. This book is a vital tool for all researching and studying circulating tumor cells.