Review ArticlesCirculating Tumor Cells: Overview and Opportunities in CytologySundling, Kaitlin E. MD, PhD*; Lowe, Alarice C. MD†Author Information *Wisconsin State Laboratory of Hygiene and Department of Pathology, University of Wisconsin, Madison, WI †Department of Pathology, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA The authors have no funding or conflicts of interest to disclose. Reprints: Kaitlin E. Sundling, MD, PhD, Wisconsin State Laboratory of Hygiene, 465 Henry Mall, Madison, WI 53706 (e-mail: [email protected]).All figures can be viewed online in color at www.anatomicpathology.com. Advances In Anatomic Pathology: January 2019 - Volume 26 - Issue 1 - p 56-63 doi: 10.1097/PAP.0000000000000217 Buy Metrics Abstract Circulating tumor cells (CTCs) have long been assumed to be the substrate of cancer metastasis. However, only in recent years have we begun to leverage the potential of CTCs found in minimally invasive peripheral blood specimens to improve care for cancer patients. Currently, CTC enumeration is an accepted prognostic indicator for breast, prostate, and colorectal cancer; however, CTC enumeration remains largely a research tool. More recently, the focus has shifted to CTC characterization and isolation which holds great promise for predictive testing. This review summarizes the relevant clinical, biological, and technical background necessary for pathologists and cytopathologists to appreciate the potential of CTC techniques. A summary of relevant systematic reviews of CTCs for specific cancers is then presented, as well as potential applications to precision medicine. Finally, we suggest future applications of CTC technologies that can be easily incorporated in the pathology laboratory, with the recommendation that pathologists and particularly cytopathologists apply these technologies to small specimens in the era of “doing more with less.” Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.