What is cancer?
The notion that cancer is an unexplored disease is just false. Scientists have long studied the mechanisms of its emergence. Cancer is a genetic disease, which doesn't mean that it is hereditary. It emerges as a result of gene breakage that can occur due to different factors. The development of cancer is a consistent accumulation of mutations in a cell that results in the cell getting cancerous properties.
There exist three types of genes which can cause cancer if they break. Proto-oncogenes are genes that are responsible for cell division, suppressor genes are genes that are responsible for interactions between cells, and repair genes are responsible for "repairing" DNA. During their lives, people become subject to different factors, many of which cause genetic damage. Oftentimes, things like tumor syndrome and high risks of cancer at a young age have to do with the breakage of repair genes. Today, we know of about 50 different genes (repair genes included), the breakage of which leads to the development of tumor syndrome, which greatly raises the risk of cancer.
If a gene gets broken, this leads to the development of a tumor. A tumorous cell stops reacting to signals and obtains new properties; it starts mutating at high speed, and sooner or later particular cells acquire the properties that let them become even more malignant and start metastasizing.
There's no such thing as "stages" of cancer
It's assumed that the first stage of cancer is the initial stage, from which all other stages develop. According to this logic, the fourth stage is the final one. Still, stage four cancer and proliferous stage one cancer are in fact two different types of cancer. Stage four cancer is cancer that has cell clones which can metastasize and have many new properties in comparison with stage one cancer cells. Such cancer has different genetics and biology.
The word "stages" is being used in oncology due to the history of cancer research. In the middle of the 19th century, German physician Rudolf Virchow came up with his theory of cancer origin where he assumed that cancer emerges from cells. Still, it was also then that the notion that cancer just grows in size became so widespread, whilst cancer actually obtains new properties, and it is for this reason that it can continue to grow. The discovery that has become breakthrough has also stalled the development of oncology for over a hundred years. For example, according to William Stewart Halsted's theory, tumors were to be removed at early stages, the more tissue eliminated from around the tumor the better. Many oncologists follow this logic up to this day.
Despite the notion of cancer stages being false, it is still useful from a practical standpoint. A tumor's biological properties manifest in its dissemination, which is what "cancer stages" account for: whether cancer will invade a muscle, metastasize, and so on. This can be used to develop a precise forecast. What's more, it is still the most convenient method of forecasting clinical outcomes.
The modern theory of neoplastic proliferation speaks to the fact that excessive elimination of tissue around the tumor is totally meaningless, as the tumor has already disseminated, it just didn't obtain particular properties. The first ones to learn that were Josh Fidler and Bernard Fisher at the end of the 20th century. In the course of their research, the scientists discovered that the amount of eliminated tissue doesn't affect survivability. They also learned that there's no need to eliminate lymph nodes, just checking whether they are affected or not is enough. This research has become a milestone one, followed by a series of other discoveries that complemented the new theory.
Starting from 1950s, oncology has taken up the trend for fewer surgical interventions when treating any types of cancer. Nowadays, the mammary gland is eliminated only if the tumor occupies it completely or has lesions all over it. In all other cases, they eliminate the tumor only and conduct biopsy of lymph nodes in order to check whether cancer has the property of affecting them. The percentage of organ-preserving surgeries is considered a measure of quality of decision making in oncology departments. Unfortunately, many oncologists in Russia still perform surgeries according to Halsted's method.
Cancer development is a stochastic process. Cancer cells disseminate from the first tumor: they get into the blood flow, lymph flow and other locations. Still, most of such cells die, and those that survive can't grow into a secondary tumor. Yet, if a single one from trillions of cells that disseminate from the initial tumor and enter other tissues attaches itself to the tissue, and will be capable of metastasizing, this would be enough to kill a person.
What causes genetic cell damage
Though age by itself doesn't damage cells in any way, the longer a person lives, the more susceptible to risk factors they become. Contacting with substances that enhance the mutation processes, tobacco, for instance, can speed up this process as well. If a person already has mutations that can lead to lung cancer, a damaged gene makes it even more probable. If repair genes don't work properly, and a person smokes, they will get cancer with an almost 100% probability.
The situation with alcohol is quite similar: remember that there are no "safe" doses of alcohol! Other carcinogens also lead to genetic cell damage. Asbestos is one of such substances; it greatly increases the risk of lung cancer in humans.
Chronic inflammation also leads to the emergence of cancer, as it involves constant tissue reparation: cells reproduce in great numbers, and sooner or later, DNA replication errs.
Another possible cause of genetic cell damage is immunological suppression. The weakening of cell immunity increases the probability of tumor emergence. Suppressing one's immune system results in a risk of melanoma. 80% of melanoma cases degenerate under the effect of immune system and not even diagnosed. Still, some tumors avoid the immune response.
Infectious agents such as bacteria and viruses can also cause genetic cell damage. Among the viruses that can directly affect DNA is the HPV (human papillomavirus) virus. Anyone who is sexually active can be infected with it. Still, having the virus doesn't guarantee that a person will have cancer. In most cases, the virus gets eliminated much like the flu virus, albeit slower. For this reason, HPV is rarely treated, as it disappears by itself. Still, that is not always the case. In some cases (with people who are 30 and older), HPV remains in the cell and causes dysplasia, which leads to cancer.
Among other risk factors are ionizing radiation (which directly damages cells), UV radiation (though it doesn't cause particular types of cancer like breast cancer), and diet (the resulting gastrointestinal diseases such as ulcer can cause cancer). It has also been proved that red meat and its derivatives increase the risks of colorectal cancer (white meat and fish don't): regular consumption of red meat can increase it by as much as 18%.
Intake of additional hormones can increase the risk of breast cancer that develops under the effect of sex hormones. Obesity and physical inactivity are among the essential risk factors of many cancer localizations.
It is also important to know about the false risk factors that have nothing to do with the disease. Among them are electromagnetic fields, antiperspirant deodorants, sugar substitute products, cancer phobia, stress, surgery, trauma or genetic inheritance (even if you do have the associated mutation, there's no telling whether it will develop into cancer).
Early detection and screening
Early detection offers an opportunity to eliminate the cell clones that could later produce malignant clones. Though treatment doesn't necessarily prevent the emergence of a fatal clone, it can at least postpone it.
While early detection focuses on detecting symptomatic cancer, screening is a way to detect cancer that has no symptoms. The problem here is that though screening provides for a better quality of treatment, it also has its downsides.
The benefits of screening can be narrowed down to the following: prolongation of life (can either happen or not), cancer prevention (in case of detection), and improvement of the quality of life (after treatment). Still, there are possible hazards, as well. Among them are false positive diagnoses and their consequences (including procedures like biopsy and diagnostic surgery that the patient doesn't actually need), overdiagnosis (detecting and treating comparatively harmless cancer, when the attempts to treat it are more dangerous than the disease itself) and such.
This is why one has to be really careful about considering the benefits and drawbacks of screening. As of today, we know of four kinds of tumors in case of which the benefits of screening outweigh the possible hazards: cervical cancer, breast cancer, colorectal cancer, and lung cancer.
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