Dielectrophoresis (DEP) is a method of manipulating, including separating, of target object (nano and/or microparticles, living cells) in the presence of a non-uniform electric field. In recent years, the method has found numerous applications in the bio-medical fields, especially in oncology, more precisely in the study of circulating tumor cells (CTCs). CTCs are cells released by a tumor during its early stages of metastasis, when secondary tumors cannot yet be detected by classical imaging methods. Thus, DEP may be a useful adjuvant method in the earlier detection of cancer. In this context, this article offers a new perspective on a topic of great interest nowadays. Presenting in the first two parts in detail the technique of DEP and the most important physical-biological characteristics of the CTCs, the article lists in the final part the most relevant and recent applications of this technique in the field of tumor cells, opening possible future research directions.