Carcinogenesis: The Development of a Cancer
TL;DR:Too Long; Didn't Read
Our understanding of what cancer is, what causes it, and how it is treated has evolved (and will continue to evolve) over time. The human body is built with trillions of cells, which are the basic building blocks of all living things. Normal cells communicate, create copies of themselves (divide), and eventually die (U.S. Department of Health and Human Services, 2018). Genetic mutations, however, can disrupt normal cell processes and lead to the uncontrolled growth of a single cell — cancer (Mukherjee, 2010, p. 6). It is this uncontrollable, pathological, cell division that creates masses of tissue (tumors) (Mukherjee, 2010, pp. 15-16).
Cancer is not one disease but a complex group of diseases that share common characteristics at the cellular level (Mukherjee, 2010, p. 573). Likewise, there is no single cause of cancer. In addition to environmental exposure (for example, alcohol, asbestos, chemicals, pollution, radiation and tobacco), hepatitis B and C viruses can lead to liver cancer, human papilloma virus can lead to cervical cancer, and poor diet can contribute to colon (colorectal) cancer (Mukherjee, 2010). There are many other known and possible causes of cancer.
Carcinogenesis is a slow, step-by-step, progression: a single normal cell becomes precancerous, then it becomes malignant (Mukherjee, 2010, p. 286). For example, smokers can develop precancerous lesions (damaged tissue) inside of their bronchi and lungs. While some lesions remain harmless, others may develop additional abnormalities and ultimately become lung cancer (Mukherjee, 2010, pp. 258-259). In this case, the progression can take 30 years or more (Mukherjee, 2010, p. 272).
Cancer is insidious: it can adapt, evolve, and overcome the most battle tested treatments. On the one hand, treatment can be successful if the disease is confined to one location and it's discovered early. On the other hand, it can move about with great stealth and attack other parts of the body — metastasize (Mukherjee, 2010, pp. 38-39).
For example, lung carcinomas can metastasize using either blood vessels or the lymphatic system. When metastasis occurs via blood vessels, it can develop much earlier, whereas metastasis via the lymphatic system is much slower. Lung cancer metastases can develop in the adrenal glands, bones, brain, liver, thoracic wall, and other locations (Popper, 2016).
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