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Unformatted text preview: How Cancer Arises H ow cancer develops is no longer a mystery. During the past two decades, investiga-tors have made astonishing progress in identifying the deepest bases of the pro-cessthose at the molecular level. These discoveries are robust: they will survive the scrutiny of future generations of re-searchers, and they will form the foun-dation for revolutionary approaches to treatment. No one can predict exactly when therapies targeted to the molecu-lar alterations in cancer cells will nd wide use, given that the translation of new understanding into clinical prac-tice is complicated, slow and expensive. But the effort is now under way. In truth, the term cancer refers to more than 100 forms of the disease. Al-most every tissue in the body can spawn malignancies; some even yield several types. What is more, each cancer has unique features. Still, the basic processes that produce these diverse tumors ap-pear to be quite similar. For that reason, I will refer in this article to cancer in generic terms, drawing on one or anoth-er type to illustrate the rules that seem to apply universally. The 30 trillion cells of the normal, healthy body live in a complex, interde-pendent condominium, regulating one anothers proliferation. Indeed, normal cells reproduce only when instructed to do so by other cells in their vicinity. Such unceasing collaboration ensures that each tissue maintains a size and archi-tecture appropriate to the bodys needs. Cancer cells, in stark contrast, violate this scheme; they become deaf to the usual controls on proliferation and fol-low their own internal agenda for re-production. They also possess an even more insidious propertythe ability to migrate from the site where they began, invading nearby tissues and forming masses at distant sites in the body. Tu-mors composed of such malignant cells become more and more aggressive over time, and they become lethal when they disrupt the tissues and organs needed for the survival of the organism as a whole. This much is not new. But over the past 20 years, scientists have uncovered a set of basic principles that govern the development of cancer. We now know that the cells in a tumor descend from a common ancestral cell that at one pointusually decades before a tumor becomes palpableinitiated a program of inappropriate reproduction. Further, the malignant transformation of a cell comes about through the accumulation of mutations in specic classes of the genes within it. These genes provide the key to understanding the processes at the root of human cancer. Genes are carried in the DNA mole-cules of the chromosomes in the cell nu-cleus. A gene species a sequence of amino acids that must be linked togeth-er to make a particular protein; the pro-tein then carries out the work of the gene. When a gene is switched on, the cell responds by synthesizing the encod-ed protein. Mutations in a gene can per-turb a cell by changing the amounts or the activities of the protein product. the activities of the protein product....
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This note was uploaded on 10/26/2011 for the course LS 2 taught by Professor Pires during the Spring '08 term at UCLA.
- Spring '08