8/24/2006 The Role of the IGF System in Cancer Growth and Metastasis: Overview and Recent Insights First published online on August 24, 2006 Endocrine Reviews, doi:10.1210/er.2006-0001 Endocrine Reviews 28 (1): 20-47 Copyright © 2007 by The Endocrine Society The Role of the IGF System in Cancer Growth and Metastasis: Overview and Recent Insights Amir Abbas Samani, Shoshana Yakar, Derek LeRoith and Pnina Brodt Departments of Medicine (A.A.S., P.B.), Surgery (P.B.), and Oncology (P.B.), McGill University Health Centre, Royal Victoria Hospital, Montreal, Québec, Canada H3A 1A1; and Division of Endocrinology, Diabetes and Bone Disease (S.Y., D.L.), Mount Sinai School of Medicine, New York, New York 10029-6574 Correspondence: Address all correspondence and requests for reprints to: Pnina Brodt, Department of Surgery, McGill University Health Center, Surgical Labs, Royal Victoria Hospital, Room H6.25687, Pine Avenue West, Montreal, Québec, Canada H3A 1A1. E-mail: pnina.brodt@muhc.mcgill.ca IGF-I receptor (IGF-IR) signaling and functions are mediated through the activities of a complex molecular network of positive (e.g., type I IGF) and negative (e.g., the type II IGF receptor, IGF-IIR) effectors. Under normal physiological conditions, the balance between the expression and activities of these molecules is tightly controlled. Changes in this delicate balance (e.g., overexpression of one effector) may trigger a cascade of molecular events that can ultimately lead to malignancy. In recent years, evidence has been mounting that the IGF axis may be involved in human cancer progression and can be targeted for therapeutic intervention. Here we review old and more recent evidence on the role the IGF system in malignancy and highlight experimental and clinical studies that provide novel insights into the complex mechanisms that contribute to its oncogenic potential. Controversies arising from conflicting evidence on the relevance of IGF-IR and its ligands to human cancer are discussed. Our review highlights the importance of viewing the IGF axis as a complex multifactorial system and shows that changes in the expression levels of any one component of the axis, in a given malignancy, should be interpreted with caution and viewed in a wider context that takes into account the expression levels, state of activation, accessibility, and functionality of other interacting components. Because IGF targeting for anticancer therapy is rapidly becoming a clinical reality, an understanding of this complexity is timely because it is likely to have an impact on the design, mode of action, and clinical outcomes of newly developed drugs.   To read this article in its entirety: http://edrv.endojournals.org/cgi/content/abstract/28/1/20