A multicellular organism can thrive only when all its cells function in
accordance with the rules that govern cell growth and reproduction.
Why does a normal cell suddenly become a “rebel,” breaking the rules,
dividing recklessly, invading other tissues, usurping resources, and in
some cases eventually killing the body in which it lives?
To understand how and why cells rebel, we need to understand the
normal functions of cell growth and reproduction. From the midnineteenth
century on, research in cell biology, biochemistry, and
molecular biology has provided astonishingly detailed information
about the molecules and processes that allow cells to divide, grow,
differentiate, and perform their essential functions. This basic
knowledge of cell biology has also led to practical discoveries about
the mechanisms of cancer. Specific molecules that control the
progression of a cell through the cell cycle regulate cell growth. An
understanding of normal cell cycle processes and how those processes
go awry provides key information about the mechanisms that trigger
cancer. Loss of control of the cell cycle is one of the critical steps in the
development of cancer.
Although cancer comprises at least 100 different diseases, all cancer
cells share one important characteristic: they are abnormal cells in
which the processes regulating normal cell division are disrupted.
That is, cancer develops from changes that cause normal cells to
acquire abnormal functions. These changes are often the result of
inherited mutations or are induced by environmental factors such as
UV light, X-rays, chemicals, tobacco products, and viruses. All evidence
suggests that most cancers are not the result of one single event or
factor. Rather, around four to seven events are usually required for a
normal cell to evolve through a series of premalignant stages into an
invasive cancer. Often many years elapse between the initial event and