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CANCER
17.1 Introduction
In multicellular organisms, the growth of cells by division is under tight
control (Chapter 15). Cells divide when stimulated with the requisite internal
and external signals (Figure 17.1). This strict control of cell division ensures
that division occurs at a rate appropriate to the structure of the tissue or
organ. In some tissues, for example bone marrow, skin and gastrointestinal
(GIT) endothelium, cells divide constantly, replacing ones that have died.
However, in other tissues, such as nervous tissue, mitosis is rare and lost cells
are not replaced. In yet other tissues, cells can commence dividing when
required as, for example, in the regeneration of liver or during the healing of
wounds in the skin. The term cancer covers a number of diseases in which the
growth of cells becomes uncontrolled. Cancer cells fail to respond to the usual
controling signals and their growth becomes unregulated. Indeed, the name
cancer comes from a Latin word meaning ‘a crab’, and describes the manner in
which the pattern of penetration into normal tissues by the abnormal growth
bears a superficial resemblance to a crab’s claw. These abnormal cells may
OBJECTIVES
After studying this chapter you should be able to:
N explain what is meant by the following terms: cancer, malignant, neoplasm,
tumor;
N discuss the incidence and epidemiology of cancer;
N describe and explain some of the environmental causes of cancer;
N outline the relationship between gene mutations and cancer;
N describe how cancer may be clinically detected;
N describe the clinical features of some cancers;
N explain how cancers may be treated.
Figure 17.1Some intrinsic and extrinsic factors
that influence cell division.Cell signaling factors
Growth factors
Hormones
Nervous control
Nutrients
Position