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Cancer Biology: How does cancer originate?
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Cancer Biology: How does cancer originate?
Evolution has given human cells the potential to grow and differentiate. This potential enables mature tissues to have the ability to maintain themselves throughout life.
This maintenance function includes the repair of wounds and the replacement of worn-out and aging cells due to long-term service to the body.
However, on the other hand, this kind of autonomy and versatility will also bring great dangers.
They allow individual cells in tissues and organs to obtain information about the entire genome, and the genome sequence is often destroyed by multiple mechanisms.
When changed, these mutated genes may give the cell a completely new and often abnormal phenotype.
Some of these inappropriate changes may change the growth cycle of cells, or cause a large number of cells to no longer follow the rules that control and maintain normal tissue structure.
Therefore, the formation of tumor cells is the result of a departure from normal development.
Although the body has a special mechanism to prevent this, tumor cells have found a way to survive.
Normal cells participate in the construction of different tissues in strict accordance with the designed procedures to enable the body to survive, while tumor cells have a completely different and more focused task.
They seem to only consider one thing: to reproduce themselves as much as possible.
Tumor originated from normal tissue
Earlier, many people thought that tumors were foreign objects implanted in patients in some way. Now, with the development of histopathology, 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 composed of a large number of cells.
In addition, a large number of facts show that various types of tumors often originate from their normal source tissues, rather than external 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 cancer cell colonies.
These new colonies, known as metastases , can usually be traced to the original site of tumor occurrence. , That is, carcinoma in situ .
Histopathology enables people to understand the relationship between the clinical manifestations of a tumor and its microstructure.
According to the different degree of invasive growth of tumors, it is divided into two major 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, with the exception of a few tumor masses that compress important tissues and organs due to expansion, the vast majority of primary tumors are benign and harmless to the host.
Tumors originate from many specific types of cells in the body
Most human tumors originate from epithelial tissue. Epithelial cells are linearly arranged lamellar cells that make up body cavities, ducts, and epidermis.
Beneath the epithelial cell layer is the basal layer (also called the basement membrane ); the basal layer separates the epithelial cells from the mesenchymal cells that play a role in supporting connections below.
The incubation of epithelial cells produces the most common tumor in humans, called cancer . More than 80% of cancer-related deaths are caused by such tumors.
These include tumors derived from the epithelial cell layer of the gastrointestinal tract.
The gastrointestinal tract includes tumors derived from the oral cavity, esophagus, stomach, small intestine and large intestine, as well as skin, breast, pancreas, lung, liver, ovary, gallbladder, and bladder.
The vast majority of malignant tumors can be divided into two categories, which reflect two important biological functions related to epithelial cells.
The main function of some epithelial cell layers is to seal the surface of cavities or ducts and protect the cells underneath.
Tumors developed from such epithelial cells are called squamous cell carcinomas , such as epithelial cells of the skin and esophagus.
There are also many epithelial tissues with special secretory cells that can release secretions into their own ducts or cavities.
This kind of epithelial tissue-derived cancer is called adenocarcinoma , such as the epithelial cells of the lung and stomach. In most cases, two types of cancer cells coexist in the tumors of these organs.
Another large type of non-epithelial tissue-derived malignant tumors are transformed from various cells that make up the hematopoietic system, including immune system cells, T lymphocytes, B lymphocytes, plasma cells and myeloid cells.
Leukemia is caused by the malignant transformation of some hematopoietic cell lines.
Tumor cells in leukemia form single-cell clusters and are scattered in the circulatory system. Lymphoid tumors can accumulate in the lymph nodes to form solid tumors.
The third category is a type of non-epithelial tissue-derived tumors, which are malignant transformations of various cells that make up the central and peripheral nervous system.
Such tumors are usually called 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. For example, melanoma is derived from pigmented melanocytes in the skin and retina.
The occurrence and development of tumors
Theoretically, tumors can be monoclonal or polyclonal in origin. In polyclonal tumors, a variety of cells cross the boundary of normal to malignant transformed cells, and thus become the ancestors of multiple genetically distinct cell subgroups in a tumor mass.
In a monoclonal tumor, only a single cell changes from a normal state to a state with cancer behavior, and thus becomes the ancestor of all cells in a tumor mass.
In fact, most human tumors are monoclonal populations, which start from a single progenitor cell and gradually move towards malignant transformation.
This has been proven many times. One of the evidence comes from the study of myeloma, which is mainly derived from the blast cell-B lymphocytes of plasma cells that secrete antibodies.
Under normal circumstances, B lymphocytes are composed of a very large number of distinct subgroups, and each subgroup secretes a specific antibody.
What’s different is that the plasma cells of myeloma patients produce the same antibodies, suggesting that they developed from a single previous cell and have a common progenitor cell.
Between the two extremes of normal tissue and highly deteriorating tumor tissue, there is a rich intermediate transition state in the body tissue morphology.
These cells in different stages of deterioration reflect the process of cells gradually changing from normal tissues to a deteriorated state with the ability to invade and metastasize.
Therefore, each phenotype of a tumor represents a stage of the tumorigenesis and development process. The history of tumor occurrence and development is a very complex process with multiple stages.
Incidence of cancer
The nature of cancer shows that it is a disease in which the body is chaotic and the biological order collapses.
In fact, there is a great chance of cancer in the body. More than 1013 cells in the body always carry this genetic information, and many parts of the body are at risk of out-of-control cell proliferation.
An average of 1016 stable cell colonies are formed in a person’s life.
Each time a new cell is produced through a complex process of cell growth and division, there are many error-prone areas in the meantime.
According to the results and incidence of clinical diagnosis around the world, some cancers have a very high risk of developing, while others are not so high.
In addition to the relatively stable incidence of certain specific cancers, certain factors can significantly increase the incidence of cancer in specific populations.
These two important factors are genetic factors and environmental factors .
Different populations carry tumor susceptibility genes very differently, and people’s environment 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.
There are indeed huge differences in the incidence of certain tumors in different populations. In China, the incidence of breast cancer is 1/6 that of the United States or Northern Europe.
After excluding genetic factors, we can conclude that as long as they experience a living environment and lifestyle similar to those of Chinese women, 85% of breast cancers that occur in the United States can theoretically be avoided.
Causes of cancer
The causes of cancer generally include the following: genetic factors, lifestyle, chemical reagents, and physical or chemical carcinogens.
Many tumors are related to genetic factors. If the immediate family members of the family have some kind of tumor, the chance of getting the tumor will increase, and it is more likely to induce tumors than external incentives.
In recent years, molecular genetic studies of tumors have shown that some genes related to cell growth and differentiation play a key role in the process of carcinogenesis.
These genes are called oncogenes and tumor suppressor genes . Their structure or function abnormalities make cells uncontrollable. Grow and eventually lead to tumors.
A century before the establishment of modern epidemiology, people discovered that the occurrence of certain cancers may be related to lifestyle.
The first report came from the British doctor John Hill, who noticed in 1761 that the development of nasal cancer was related to long-term excessive use of nasal smoking.
Fourteen years later, Percivall Pott, a surgeon in London, reported on a considerable number of teenagers with skin cancer of the scrotum he had encountered, all of whom had experience as chimney cleaners.
Less than three years later, the Danish Scavengers Association required its members to take a bath every day to remove possible carcinogens from the skin.
This measure made the incidence of scrotal cancer in continental Europe much lower than that in the United Kingdom after a century.
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 application of the same place on the skin of rabbit ears will induce malignant tumors after a few months.
This research is a huge improvement because it directly reflects the carcinogenic effects of chemicals.
Until 1940, British chemists extracted several significant carcinogenic components from coal tar, all of which can cause cancer on the skin of mice.
The 3-methylcholanthrene, benzo[α]pyrene, and 1,2,4,5-diphenyl-[α, h]-anthracene in the components are all common combustion products.
These findings suggest that some Some chemicals that enter the body can disrupt cells and tissues and eventually cause tumors to occur.
The same is true for X-rays, which can induce cancer through a seemingly different mechanism of action.
In the first 10 years of the 20th century, researchers discovered that viruses can infect chickens and cause leukemia and chicken tumors.
By the middle of the 20th century, a series of viruses were discovered that can 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 mechanism of these three carcinogens did not make great progress until people had made some achievements in the genetics of Drosophila. In 1927, Hermann Muller discovered that X-ray irradiation can induce mutations in the genome of Drosophila melanogaster.
More importantly, the genetic information contained in this genome change has also changed.
This also indicates a mechanism by which X-rays induce cancer: The genes of normal cells can be changed by radiation, and this change is likely to cause the cells to transform into a malignant state.
1. “The biology of CANCER ” second edition. Robert.A Weinberg
Cancer Biology: How does cancer originate?
(source:internet, reference only)