**1. Introduction**

Cholesterol is an essential component of cellular membrane. It serves as a spacer between the hydrocarbon chains, functions as dynamic glue during membrane assembly, and plays a crucial role in the stability, architecture, dynamics, and function of cellular membrane [1, 2]. In addition, cholesterol is involved in vesicle trafficking and transmembrane receptor signaling [3–6]. Meanwhile, cholesterol itself is also as a precursor of steroid hormones and sterols in the steroidogenesis [6–8]. The vesicle trafficking, receptor-mediated signaling, and steroidogenesis further lead to specific biological responses and regulate different cellular functions such as membrane biogenesis, cell growth, proliferation, apoptosis and migration, as well as tumor progression [6–8].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Due to the key physiologicalroles that cholesterol plays,the circulating and cellular cholesterol levels in our body are tightly regulated by a physiological balance of cholesterol biosynthesis, cholesterol catabolism, cholesterol transportation (influx and efflux), dietary cholesterol absorption, andcholesteroldepletion.Higher cholesterol, alsoknownashypercholesterolemia, is a risk factor for a variety of human diseases such as cardiovascular diseases, dyslipidemia, Alzheimer'sdisease,HIVdyslipidemia, chronic inflammation, anddevelopingdiabetes.Earlier data also indicates that accelerated cholesterol metabolism and elevated cholesterol levels contribute tothehallmarksof cancerdevelopmentandmalignanttransformation[9–15].Cancer cells need excess cholesterol and intermediates of the cholesterol biosynthetic pathway to maintain a high level of cell growth and proliferation. Meanwhile, cholesterol is capable of regulating multiple signaling pathways involved in carcinogenesis, cancer cell migration, and tumor progression and is also involved in chemosensitivity and chemotherapy resistance of cancer cells [9–19]. It is very important to understand cholesterol as an important factor contributing to carcinogenesis and tumor progression and to elucidate the regulation of cholesterol metabolism as a new strategy for searching cancer prevention and therapy drugs.
