What is metastasis and why does it occur? - medical - 2023
- Metastasis: the worst outcome
- Some figures
- The mechanism of metastasis
- What promotes metastasis?
Metastasis is a term that refers to a cancerous focus that has spread to a different organ from which it started. It is this dispersal capacity that makes cancer a lethal disease, since it is estimated that more than 90% of deaths in patients from undetected cancers are due to their metastasis.
Today we have in front of us one of the terms most feared by the general population, because unfortunately cancer is a disease that, far from disappearing, is increasingly spreading through society in terms of knowledge and epidemiology. The annual incidence of this disease (number of new cases) is almost 500 patients per 100,000 people. A figure of vertigo.
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Therefore, even if we do not want to look this monster in the eye, it is necessary to know the mechanisms that lead to the death of the patient due to a pathology as hard as cancer. Knowledge is power, and of course, the first weapon to be able to approach the disease from a medical point of view.
Metastasis: the worst outcome
We cannot begin to talk about metastasis without defining some terms when it comes to cancer. This disease responds to a set of related pathologies that derive from the uninterrupted atypical growth of some cells of a tissue, which spread to other organs over time.
In a carcinogenic process, cell turnover is disrupted and works in an atypical way, since cells that should die do not do so and new cell bodies are formed when they are not needed, which produces the tumors that unfortunately we know so well.
Cancer cells are less specialized than normal cells and ignore apoptosis (programmed cell death) processes. This, added to the fact that they are usually capable of evading the patient's immune system, is a cocktail to say the least lethal without proper treatment.
The link between metastasis and cancer is absolute, since all metastasis comes from cancer, but not all cancer ends up leading to it. We present some data regarding this pathology collected by the World Health Organization.
- Cancer is the second leading cause of death in the world. In 2015 there were almost 9 million deaths. One in six deaths is from cancer.
- About 70% of deaths from this disease occur in low- and middle-income countries.
- Smoking is the main risk factor, as it is associated with 22% of deaths in patients with carcinogenic processes.
- Cancers such as lung cancer, unifying all its variants, present a relative survival rate of the patient after five years of 23%.
- 92% of deaths from undetected cancers are due to their metastasis.
As we can see, we are facing a bleak outlook. Cancer rates in women are up 1% from last year, but even so, more and more is known about the disease and its predisposing risk factors. For example, it is estimated that a third of cases are associated with a high body index, an inadequate diet, lack of exercise, smoking and alcoholism.
The mechanism of metastasis
Once the foundations of this disease have been established, the metastasis process is much easier to understand. As we have previously anticipated, This is characterized by the migration of cancer cells to a different tissue from the one from which they originated.
Normally, this process begins when these cells of atypical growth detach from the original tumor, migrate through the circulatory or lymphatic system and settle in a new tissue, also replicating in an uncontrolled way in it. It is important to note that the new tumor shares characteristics with the first, since they are composed of the same cell types.
Thus, a breast cancer that has spread to the liver is considered a metastatic breast cancer and not a liver cancer. Some of the factors that promote this process are the following:
- The type of cancer, as some are more likely to spread than others.
- The rate of tumor growth.
- Other intrinsic and extrinsic factors to the disease.
Also, some types of cancer tend to spread to specific parts of the body. For example, malignant tumor processes in the rectum and colon are more likely to spread to the liver and lungs than to any other part of the body.
The phases of metastasis, in turn, can be defined in five simple steps that occur in a “cascade”. These are the following:
- Dissociation- A tumor cell breaks away from the primary tumor and escapes from its area.
- Invasion: Cancer cells infiltrate the stroma and migrate through the basement membrane that constitutes the endothelium of blood vessels.
- Intravasation: tumor cells enter the vascular system after having overcome the barrier of the extracellular matrix.
- Extravasation: the passage through which these cell bodies spread to other organs.
- DormancyThese cells can remain "silent" in new tissues for several years before expressing themselves.
As we can see, as if it were a sentient parasite, cancer cells circumvent all the physical barriers necessary to be able to infiltrate the bloodstream and spread.
What promotes metastasis?
We are facing a question that does not have an answer as simple as one might expect, because unfortunately, much information in the world of cancer is still unknown to us. Literature review articles, for example, highlight that there is an important correlation between the probability of metastasis and certain groups of genes present in the cells of the primary tumor (which are expressed, for example, with adhesion proteins, cell motility and degrading protease activity of the womb).
These genetic changes at the cellular level are probably transient or permanent, promoting a tumor cell to reach a metastatic state. For example, studies have found that a gene located on chromosome 7 may be closely related to this process. The protein produced by this gene, called "twist", is essential for the formation of embryonic tissues, but it is completely deactivated when the fetus is already formed.
This protein does not exist in normal adult cells or in those that make up the primary tumor, but it appears to be present in metastatic cell bodies. We go further, because when metastatic cells are inoculated in laboratory animals with the gene producing "twist" deactivated, they develop a primary tumor but not a metastatic phenomenon. When cell body inoculation is done with the active gene, animals develop both a primitive tumor and the metastasis itself.
It has also been discovered that, for this dreaded process to occur, a process of angiogenesis is essential, that is, the formation of blood vessels around the tumor, which provides it with nutrients and oxygen and allows the subsequent transport of the cell to others. tissues through the bloodstream.
As we have seen, We still have a long way to go as a society to understand the mechanisms of cancer and how to fight it. Although studies such as the gene encoding the "twist" protein are encouraging, the researchers themselves emphasize that there are many other regulatory genes with similar properties, which undoubtedly need to be investigated, since it is more than likely that they play essential roles in the spread of cancer.
There are also multiple medical studies in charge of identifying genes both promoters and suppressors of metastasis, for example, more than 10 years ago the first suppressor gene of the aforementioned "metastatic cascade" was discovered, NM1.
Despite all these open fronts, human beings are playing a fierce battle against cancer: resources and time are limited, and obtaining knowledge is the first step to be able to fight the disease effectively. Of course, the bibliography is extensive and the number of open investigations astronomical, so there is nothing left to do but trust the scientific method and wait.