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Introduction

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High-Yield Terms

  • Carcinogen: any substance, such as a chemical, or any type of radiation that is directly involved in causing cancer

  • Neoplasm: any abnormal mass of tissue, medically synonymous with the term tumor

  • Malignancy: medically describes any condition that becomes progressively more severe, with respect to cancers the term characterizes invasiveness and the tendency to metastasize

  • Metastasis: refers to the spread of cancer from a site of origin to a new organ or another part of the body

  • Proto-oncogene: any normal gene that can become an oncogene due to gene mutation or abnormal expression

  • Oncogene: any gene that has the potential to cause cancer, in tumor cells, these genes are often mutated or expressed at high levels

  • Tumor suppressor: any gene that prevents the unregulated growth of cells, loss of function of this class of gene can result in cancer, also called antioncogene

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Cancer Defined

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Cancers, in the broadest terms, are a wide array of diseases typified by unregulated cell growth. The medical and biological term is neoplasm and defines an abnormal tissue that grows more rapidly than normal and continues to grow and proliferate in the absence of the originating growth signal. Neoplasms are transformed cells that can also harbor the characteristics of immortality. Transformation is a multistep process which results in the generation of the neoplastic cells. Immortalization refers to cells with unlimited life span but is not directly associated with aberrant growth or malignancy. Neoplasms can be benign or malignant. In the strictest sense, malignancy is defined as the ability to generate invasive tumors when cells are transplanted in vivo. However, medically this is not a useful definition due to the time required for the assessment of this capability. Therefore, it is more appropriate to define a malignant tumor, or mass, by its potential to worsen, to invade the surrounding tissues, and to exhibit the potential for metastases. Metastasis is the ability of cells from a tumor to break away from the original mass and spread to another location in the body. Although these terms broadly define all cancers, different types of cancers from different tissues exhibit a wide range of altered characteristics (Figure 52-1).

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FIGURE 52-1:

Some biochemical and genetic changes occurring in human cancer cells. Many changes are observed in cancer cells with many of the most significant diagrammed here. The roles of mutations in activating oncogenes and inactivating tumor suppressor genes are discussed in the text. Abnormalities of cell cycling and of chromosome structure, including aneuploidy, are common. Alterations of microRNA molecules that regulate gene activities have been reported, and the relationship of stem cells to cancer cells is a very active area of research. Telomerase activity is often detectable in cancer cells. Tumors sometimes synthesize certain fetal antigens, which may be measurable in the blood. Changes in plasma membrane constituents (eg, alteration of the sugar chains of various glycoproteins—some of which are cell adhesion ...

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