Cancer is a diseases characterized by uncontrolled multiplication and spread of abnormal forms of the body's own cells. The terms cancer, malignant neoplasm (neoplasm simply means 'new growth') and malignant tumor are synonymous. Both benign and malignant tumors manifest uncontrolled proliferation, but the latter are distinguished by their capacity for dedifferentiation, their invasiveness and their ability to metastasize (spread to other parts of the body). In this chapter, we shall be concerned only with the therapy of malignant neoplasia or cancer. The appearance of these abnormal characteristics reflects altered patterns of gene expression in the cancer cells, resulting from genetic mutations. In simple terms, cancer is a group of more than 100 diseases that develop across time and involve the uncontrolled division of the body's cells. Although cancer can develop in virtually any of the body's tissues, and each type of cancer has its unique features, the basic processes that produce cancer are quite similar in all forms of the disease.