This book describes molecular processes whose deregulation is important in the formation of tumors. The material is developed from basic cell signaling pathways to their roles in the clinical manifestation of specific cancers. Topics covered include molecular events intrinsic to tumor cells (leading to growth deregulation, extended lifespan, and the ability to invade surrounding tissue), protective mechanisms that prevent transformation (including DNA repair and epigenetic regulation), tumor-host interactions (with the endocrine system, the immune system, and blood vessel formation), and the underlying molecular defects of individual cancers.