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Cancer Biology: The Nature of Cancer
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Cancer Biology: The Nature of Cancer
Evolution has given human cells the potential to grow and differentiate, a potential that enables mature tissues to maintain self-maintenance throughout life.
This maintenance includes the repair of wounds and the replacement of worn-out cells from long-term service to the body.
On the other hand, however, this autonomy and versatility also poses great dangers, allowing individual cells in tissues and organs to access information from the entire genome, whose sequence is often disrupted by multiple mechanisms When altered, these mutated genes can give cells a completely new and often abnormal phenotype.
Some of these inappropriate changes can alter the cell’s growth cycle, or cause large numbers of cells to no longer follow the rules that govern and maintain normal tissue structure.
Thus, the formation of tumor cells is the result of a departure from normal development. Although the body has special mechanisms to prevent this from happening, tumor cells have found a way to survive.
Whereas normal cells are strictly programmed to participate in the construction of different tissues that allow the body to survive, tumor cells have a different and more focused task that seems to be concerned with only one thing: to reproduce themselves as much as possible.
Tumors originate from normal tissue
Earlier, many people believed that a tumor was a foreign body implanted in a patient in some way, but now, with the development of histopathology, by comparing normal tissue sections and tumor tissue sections, it is found that tumor tissue is also different from other tissues. Like normal tissue, it is made up of a large number of cells.
In addition, numerous facts show that tumors of various types often arise from their own tissues of normal origin, rather than from foreign invaders. However, tumors do have the ability to migrate in the body. In many patients, cancer cells can spread in the body and form new colonies of cancer cells. These new colonies, known as metastases , can often be traced back to the original site of tumorigenesis. , namely carcinoma in situ .
Histopathology enables one to understand the relationship between the clinical manifestations of tumors and their microstructure. According to the degree of invasive growth of tumors, they are divided into two categories. Those that only grow in one place and do not invade adjacent tissues are called benign tumors , while those that can invade adjacent tissues and metastasize are called malignant tumors .
In fact, the vast majority of primary tumors are benign and harmless to the host, with the exception of a few tumor masses that compress vital tissues and organs due to expansion.
Tumors arise from many specific types of cells in the body
Most human tumors originate from epithelial tissue. Epithelial cells are the linearly arranged lamellar cells that make up the body cavities, ducts, and epidermis. Beneath the epithelial layer is the basal layer (also called the basement membrane ); the basal layer separates the epithelial cells from the cells of the mesenchymal layer that support junctions below.
Incubation of epithelial cells produces the most common tumors in humans, called carcinomas . These tumors account for more than 80% of cancer-related deaths. These include tumors derived from the epithelial cell layer of the gastrointestinal tract, which in turn includes the mouth, esophagus, stomach, small and large intestines, and tumors of skin, breast, pancreas, lung, liver, ovary, gallbladder, and bladder.
The vast majority of malignancies can be divided into two categories, reflecting two important biological functions associated with epithelial cells, respectively. Some layers of epithelial cells whose primary role is to seal off the surface of a cavity or duct and protect the cells underlying it , such as those of the skin and esophagus, develop from tumors called squamous cell carcinomas . There are also many epithelial tissues with special secretory cells that can release secretions into their own ducts or cavities. This epithelial-derived cancer is called adenocarcinoma , such as lung and stomach epithelial cells. In most cases, both types of cancer cells coexist in tumors in these organs.
Another major category of malignant tumors of non-epithelial origin is transformed from various cells that make up the hematopoietic system, including cells of the immune system, T lymphocytes, B lymphocytes, plasma cells and myeloid cells. Leukemia is caused by the malignant transformation of some hematopoietic cell lines. The tumor cells in leukemia form a single-cell colony and are scattered in the circulatory system; while lymphoid tumors can gather in the lymph nodes to form solid tumors.
The third major category is a class of tumors of non-epithelial origin, which are malignant transformations of various cells that make up the central and peripheral nervous systems. Such tumors are often referred to as primitive neuroectodermal tumors , including gliomas, Glioblastoma, neuroblastoma, schwannoma, and medulloblastoma .
In addition, there are some tumors that are not suitable for classification into the above types, such as melanoma, which is derived from pigmented melanocytes in the skin and retina.
In theory, tumors can originate from either monoclonal or polyclonal origin. In polyclonal tumors, multiple cells cross the boundary of normal to malignantly transformed cells and thus become the respective ancestors of multiple genetically distinct subsets of cells within a tumor mass.
In a monoclonal tumor, only a single cell transitions from a normal state to a state with cancerous behavior, becoming the progenitor of all cells in a tumor mass.
In fact, most human tumors are monoclonal populations, starting from a single progenitor cell and progressing to malignant transformation.
This has been proven many times, and one piece of evidence comes from studies of myeloma, which are primarily blast-B lymphocytes derived from antibody-secreting plasma cells.
Typically, B lymphocytes are composed of extremely numerous and distinct subpopulations, each of which secretes a specific antibody.
In contrast, the plasma cells of myeloma patients produced the same antibodies, suggesting that they developed from a single previous cell and shared a common progenitor.
Between the two extremes of normal tissue and highly deteriorating tumor tissue, there is also a rich intermediate transition state in the body’s tissue morphology.
These cells in different stages of deterioration reflect the process of cells gradually changing from normal tissue to a deteriorated state with the ability to invade and metastasize.
Therefore, each phenotype of a tumor represents a stage in the tumorigenesis and development process. The occurrence and development of tumor is a multi-stage and very complex process.
Incidence of cancer
The very nature of cancer suggests that it is a disease in which the organism is in chaos and the biological order collapses.
In fact, there is a great chance of developing cancer in the body. More than 1013 cells in the body always carry such genetic information, and there is a risk of uncontrolled cell proliferation in many parts of the body.
An average of 1016 stable cell colonies are formed in a person’s lifetime, and each time a new cell is produced through a complex process of cell growth and division, there are many error-prone places in between.
Some cancers are at very high risk, while others are not so high, based on the outcomes and incidence of clinical diagnoses around the world.
In addition to the relatively stable incidence of some specific cancers, certain factors can significantly increase the incidence of cancer for some specific populations.
These two important factors are genetic factors and environmental factors .
There are great differences in tumor susceptibility genes carried by different populations, and the environment in which people live also has a significant impact on the incidence of tumors. The environmental factors referred to here include air, moisture and living habits in a broad sense.
Cause of cancer
The causes of cancer generally include the following: genetic factors, lifestyle, chemical agents , and physical or chemical carcinogens.
Many tumors are related to genetic factors. If there is a certain tumor in the immediate family members of the family, the risk of developing the tumor will also increase, and the tumor is more likely to be induced under external incentives.
Molecular genetic studies of tumors in recent years have shown that some genes related to the growth and differentiation of cells play a key role in the process of carcinogenesis.
These genes are called oncogenes and tumor suppressor genes , and their abnormal structure or function allows cells to be uncontrolled. grow and eventually lead to tumorigenesis.
A century before the establishment of modern epidemiology, it was discovered that the occurrence of certain cancers may be related to lifestyle.
The first report came from the English physician John Hill, who in 1761 noted the development of nasal cancer in relation to chronic excessive nasal smoking.
Fourteen years later, Percivall Pott, a surgeon in London, reported on the number of teenage scrotal skin cancer patients he had encountered who had worked as chimney sweeps. Less than three years later, the Danish Scavengers Association required its members to bathe every day to remove possible carcinogens from their skin, a measure that kept the incidence of scrotal cancer in continental Europe much lower than in Britain a century later.
Coal tar condensate, similar to the carcinogen in PercivallPott’s research, was used to induce skin cancer in rabbits in the early 20th century.
Repeated smearing on the same area of the rabbit ear skin can induce malignant tumors within a few months. This research is a huge advance because it directly demonstrates the carcinogenic effects of chemicals.
Until 1940, British chemists extracted several significantly carcinogenic components from coal tar, all of which were able to cause cancer in the skin of mice. 3-methylcholanthracene, benzo[α]pyrene, and 1,2,4,5-diphenyl-[α,h]-anthracene are all common combustion products.
These findings suggest that a certain These chemicals that enter the body can disrupt cells and tissues and ultimately lead to tumorigenesis. The same goes for X-rays, which can induce cancer through an apparently different mechanism of action.
In the first decade of the 20th century, researchers discovered that viruses could infect chickens and cause leukemia and chicken tumors. By the mid-20th century, a series of viruses had been discovered that could induce tumors in rabbits, chickens, mice, and rats.
Therefore, people explore the causes of tumors mainly from three different aspects: chemical, viral, and physical.
The carcinogenic mechanisms of these three carcinogens did not make great progress until some results were obtained from genetic studies of Drosophila.
In 1927, Hermann Muller discovered that X-ray irradiation can induce mutations in the Drosophila melanogaster genome, and more importantly, the genetic information contained in the genome changes. It also points to a mechanism by which X-rays induce cancer: the effects of radiation can cause genetic changes in normal cells, and this change is likely to lead to the transformation of cells into a malignant state.
1. The biology of CANCERsecond edition. Robert.A Weinberg
Cancer Biology: The Nature of Cancer
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