Review ArticlesTumor Heterogeneity in Breast CancerBadve, Sunil MD, FRCPath; Gökmen-Polar, Yesim PhDAuthor Information Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, IN S.B. is supported by the Susan G. Komen for the Cure and 100 Voices of Hope. The authors have no conflicts of interest to disclose. Reprints: Sunil Badve, MD, FRCPath, Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, 350 West 11th Street, IUHPL 4050, Indianapolis, IN 46202 (e-mail: [email protected]). Advances In Anatomic Pathology: September 2015 - Volume 22 - Issue 5 - p 294-302 doi: 10.1097/PAP.0000000000000074 Buy Metrics Abstract Tumor heterogeneity is the topic de jour, partly because molecular biologists and researchers are identifying it using sophisticated gene/DNA analysis techniques. Clinicians and pathologists are well acquainted with marked variability in clinical presentations, tumor histology, and, more importantly, clinical outcomes of their patients. In this review, we address these issues head-on and document that tumor heterogeneity is an old friend (or, more correctly, a foe). We described heterogeneity that exists at all levels—clinical, histologic, and molecular—and briefly outline the strategies that have been used by clinicians and pathologists to tackle this complicated issue. Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.