The Nature of Cancer
2.1 Tumors arise from normal tissues
Evidence accumulated that tumors of various types, rather than invading the body from the outside world, often derive directly from the normal tissues in which they are first discovered. However, tumors did seem to be capable of moving within the confines of the human body。
2.2 Tumors arise from many specialized cell types throughout the body
2.2.1epithelial tissues tumors
The majority of human tumors arise from epithelial tissues. Epithelia are of special interest here, because they spawn the most common human cancers—the carcinomas.
Tumors that arise from epithelial cells forming these protective cell layers are termed squamous cell carcinomas(鳞癌).
Many epithelia also contain specialized cells that secrete substances into the ducts or cavities that they line. This class of epithelial cells generates adenocarcinomas(腺癌).
2.2.2 nonepithelial tissues tumors
The remainder of malignant tumors arise from nonepithelial tissues throughout the body.
The first major class of nonepithelial cancers derive from the various connective tissues, all of which share a common origin in the mesoderm of the embryo. These tumors, the sarcomas, constitute only about 1% of the tumors encountered in the oncology clinic.
The second group of nonepithelial cancers arise from the various cell types that constitute the blood-forming (hematopoietic) tissues, including the cells of the immune system.
The third and last major grouping of nonepithelial tumors arises from cells that form various components of the central and peripheral nervous systems.
2.2.3 Some types of tumors do not fit into the major classifications
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2.4 Cancers seem to develop progressively
Between the two extremes of fully normal and highly malignant tissue architectures lies a broad spectrum of tissues of intermediate appearance.
2.5 Tumors are monoclonal growths
肿瘤为单克隆生长
2.6 Cancer cells exhibit an altered energy metabolism
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2.7 Cancers occur with vastly different frequencies in different human populations
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2.8 Te risks of cancers often seem to be increased by assignable influences including lifestyle
Evidence that certain kinds of cancers are associated with specifc exposures or lifestyles is actually quite old, predating modern epidemiology by more than a century.
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Perhaps the most compelling association between environmental exposure and cancer incidence was forged in 1949 and 1950 when two groups of epidemiologists reported that individuals who were heavy cigarette smokers ran a lifetime risk of lung cancer that was more than twentyfold higher than that of nonsmokers. The initial results of one of these landmark studies are given in Table 2.6.
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2.9 Specifc chemical agents can induce cancer
文献记载的由化学致癌物诱导的肿瘤的第一次实例
As a consequence, those intent on uncovering the origins of human cancer were pulled in three different directions, since the evidence of cancer causation by chemical, viral, and radioactive agents had become compelling
reference
- The Biology of Cancer, Second Edition；Chapter 2 The Nature of Cancer
