What is Cancer?
The term cancer (or malignant tumor ) indicates a group of pathologies characterized by uncontrolled cellular replication and diffusion.
In addition to increasing the number of cancer cells, malignant growth has the ability to infiltrate and destroy nearby healthy structures. The malignancy rate is also determined by the relatively rapid growth rate and the ability to originate distant neoformations (metastases) by haematic or lymphatic diffusion of cancer cells. All this distinguishes a cancer from a benign tumor, which has a tendentially slow growth confined to the place of origin; it should however be specified that, over time, some types of benign tumors may evolve into malignant neoplasms.
The terms malignant tumor, cancer and malignant neoplasia are to be considered synonymous.
Normal and uncontrolled cellular growth
Cancer cells lose the structure and function of healthy tissue cells, from which they derive, due to their inability to adequately differentiate.
In normal tissues, cells reproduce to meet the various needs of the body, such as the growth or replacement of dead or damaged cells. In these tissues, cell proliferation and differentiation are subjected to close biochemical control. The cells, in fact, divide controlled by various growth stimuli and are equipped with defense mechanisms capable of slowing down the development processes, allowing them to repair any anomalies; if this does not happen, the cell undergoes a process of programmed death called apoptosis .
The image shows a possible process of carcinogenesis: the transformation of normal cells into cancerous is the result of a series of mutations. In cancer, all these regulatory processes are compromised and the tumor cells reproduce uncontrollably and elude the aforementioned defense mechanisms. At the origin of this phenomenon there are several genetic alterations which, when added together, blow up the control mechanisms already mentioned. It is therefore not sufficient for a single regulation mechanism to be defective, but errors need to develop on several fronts. In particular, these alterations lead to an aberration in the expression of proto-oncogenic genes.
A proto-oncogen is a physiologically involved gene in the regulation of cellular life, which can become oncogenetic (acquiring the ability to generate a neoplasm) following mutations or an increase in its expression. Following a multi-stage process, proto-oncogenes can therefore become oncogenetic, and only then will cancer develop. Oncogenetic genes are in fact able to overexpress or under-express proteins that regulate certain biochemical growth processes, causing preferential and accelerated cell growth.
In the same way, a cancer can also derive from the inhibition of tumor suppressor genes; these genes, called oncosuppressors, code for proteins that protect the cell from the accumulation of potentially tumor mutations.
Once triggered, uncontrolled cell growth can lead to the invasion of surrounding tissues and, often, also the invasion of tissues that are far from the site of origin (through the blood or lymphatic dissemination of cancer cells); this phenomenon is called metastasis . As anticipated, all these characteristics are typical of a cancer (or malignant tumor or malign neoplasm); in the benign tumor, on the other hand, the cells substantially maintain the same structure and function as the normal cells of the tissue from which they come. Furthermore, although it also proliferates autonomously, a benign tumor expands without penetrating the surrounding tissues and does not undergo metastasis.
Classification and nomenclature
The mutated cells can evolve into various types of tumors, each with its own aetiology.
The different types of tumors can be classified according to three parameters:
- Histology of affected proliferating cells;
- Aggressiveness and expected clinical course (both for malignant and benign tumors);
- Tumor staging (only for malignant tumors).
The nomenclature of the tumors is based on the typology of the tissue of origin, for example: carcinoma (originates from epithelial tissue), sarcoma (originates from muscle or connective tissues), melanoma (originates from melanocytes), leukemia and lymphoma (respectively of hematologic origin or lymphatic).
Signs and symptoms
From the moment it begins to develop, the cancer grows very rapidly and exponentially but, despite this, it does not initially produce symptoms. The first signs begin to appear only when the cancerous mass reaches certain dimensions.
Furthermore, the first symptoms that appear are often non-specific, in the sense that they can also be caused by pathologies other than cancer.
There are more than 100 different types of cancer that affect humans and the clinical manifestations of each vary considerably; it is therefore difficult to produce a definitive list of all possible signs and symptoms. In this regard, the American Cancer Society has published what are the main warning signs for the early detection of cancer. It is very important, in fact, that patients learn to recognize in these symptoms warning signs that deserve immediate insights, since the cancer is most effectively treated when it is diagnosed in a timely manner.
The main warning signs for cancer are:
- Continuous and unexplained weight loss;
- Frequent headaches with vomiting;
- Localized pains;
- Unusual mass or swelling;
- Recurrent and unexplained fever;
- Significant pallor and energy loss;
- Change of habits in going to the body and urinating;
- Unusual discharge or bleeding;
- Thickening or lump in the breast or other parts;
- Indigestion and difficulty swallowing;
- Obvious changes in warts or moles;
- Nagging cough or change of tone of voice.
When you experience unusual symptoms, it is advisable to consult a doctor.
Causes
It is very difficult to pinpoint which cancer triggers an individual, as most cancers can have multiple causes. Furthermore, the genetic mutations that lead to the onset of cancer can be caused by factors of various kinds, which contribute to the development of the disease with one another.
Environmental factors
This category does not only include the factors that affect the environment surrounding the individual - such as, for example, exposure to air pollution or solar radiation - but also other elements, including the economic factor and its style of life.
- Atmospheric pollution : some studies have shown that in people who breathe polluted air for many years, the risk of contracting cancer increases; in particular an increase in mortality due to cancer has been demonstrated, especially in those subjects who are more exposed to fine dust (polluting dust with a diameter of less than 2.5 microns).
- Chemical factors : chemicals capable of causing DNA mutations are called mutagens ; for this characteristic, many of these substances can also cause cancer and are therefore known to be carcinogenic . Epidemiological studies have shown that certain types of cancer can be found above all in some classes of workers. The best known example is perhaps that of lung and pleural cancer (the membrane that covers them) due to the exposure and inhalation of asbestos fibers (otherwise known as asbestos). Likewise, people exposed to substances such as hexavalent chromium, nickel and tar are at greater risk of developing lung cancer.
Benzene, a very common organic solvent that is also found inside cigarettes, promotes the onset of leukemia.
Polycyclic aromatic hydrocarbons are substances found within coal and oil; they are present in car exhaust gases and also derive from the combustion of wood and fossil fuels; exposure to these compounds promotes the appearance of bladder cancer.
- Ionizing radiation : ionizing radiation is generated following nuclear reactions of both artificial and natural origin (such as those that occur on the surface of the sun). These radiations are able to penetrate the matter and hit the molecules contained within the cells. When the genetic material is affected, this can break down leading to the deactivation of one or more of the genes affected, the elimination of part of the DNA sequences and mutations of various kinds. If the damage is quite consistent, in general, one goes to cell death; if the damage is small, the cell can survive in a mutated form, then proliferate giving rise to the neoplasm, which is more likely if the tumor suppressor genes (tumors-suppressing genes that are capable of being affected and mutated) are affected and mutated to control oncogenes by stopping uncontrolled cell growth).
- X-rays : these radiations are used in medical diagnostic and therapeutic fields. The risk of developing a tumor when exposed to this type of radiation tends to accumulate with the dose.
- Ultraviolet rays : these rays, generated by the sun, are useful to the body, since they are necessary for the production of vitamin D; however, sun exposure in the middle of the day damages the skin, increasing the risk of skin cancer; burns in particular increase the risk of contracting melanoma.
- Lifestyle : the lifestyle of each individual greatly affects the risk of incurring neoplastic diseases. Tobacco smoke is the most important risk factor; this, in fact, not only is able to induce mutations in tumor suppressor genes, but favors the development of the tumor once they have already occurred; it also has a negative effect on the immune system, depressing it. It has been shown that smoking causes more than 90% of lung cancers and even other types of cancer, including cancer in the oral cavity, larynx, esophagus, bladder, kidneys, pancreas, colon, and stomach and breast.
Even the excessive consumption of alcoholic beverages is able to favor the onset of cancer; recent studies have shown that the tumor caused by alcohol is not only found in subjects who abuse it, but also in subjects who make moderate consumption. The tumors that can be caused by alcohol are those in the mouth, the esophagus, the larynx and pharynx, the colon and the breast.
- Nutrition : nutrition plays a fundamental role in the risk of contracting the cancerous pathology; it has been shown that a diet rich in salt, protein and animal fats, and poor in vegetable fibers, vitamins and mineral salts, greatly increases the risk of developing some forms of cancer. Although there is not enough evidence to suggest that a vegetarian diet can help prevent the onset of the disease, it is now recognized that excessive consumption of red meat increases the risk of contracting some forms of cancer. Improper nutrition can also lead to overweight and obesity; in this regard, it seems that there is a relationship between this pathology and the onset of colon cancer, endometrium, breast and gall bladder.
- Lack of exercise : lack of exercise contributes to the onset of cancer, not only in people suffering from obesity or who have an inadequate diet, but also in normal-weight people. Various studies have shown that increasing the frequency and intensity of exercise can decrease the chances of getting breast, uterine and bowel cancer.
Infectious factors
Among the infectious agents capable of causing cancer are viruses, bacteria, mycobacteria and parasites. Among these, viruses are the agents most commonly responsible for the development of cancer.
Viruses capable of developing tumors are called oncoviruses . The best known are the Papilloma virus (cause of cervical cancer ), human Herpesvirus 8 (cause of Kaposi's sarcoma ), hepatitis B and C viruses (cause of hepatocellular carcinoma ) and Epstein Barr virus ( which generally causes mononucleosis, but in Africa is responsible for the onset of Burkitt 's lymphoma) .
The bacterium Helycobacter pylori - usually responsible for gastritis and gastric ulcers - can be easily eradicated, but appears to be implicated in the onset of some stomach tumors.
HERITAGE factors
In reality, when it comes to cancer, it is more correct to speak of " familiarity " than of hereditary factors. The pathology, in fact, is not transmitted from one generation to another through genes; what is transmitted instead is the greater predisposition to develop the disease. Cells containing mutated genes that facilitate the onset of cancer can therefore be inherited, but more errors must occur and be added, on several fronts, to get to the development of the tumor.
Despite the large number of factors that contribute to the development of cancer, over 30% of cancers can be avoided by reducing the main risk factors.
Many deaths caused by cancer could be avoided by eliminating smoking, leading to a healthy lifestyle and following a balanced diet accompanied by constant exercise.
Treatment
The type of treatment adopted varies according to the type of tumor, its stage of development and the condition of the patient.
The main types of treatment used are:
- Surgery : surgical treatment is the one most used to remove solid tumors. It is the preferable treatment in the case of benign tumors and is important in the diagnostic procedure, as it allows to visualize the tumor mass and to be able to perform biopsies.
- Antineoplastic chemotherapy : the purpose of antineoplastic chemotherapy is to block the uncontrolled cellular division that characterizes tumors. Drugs are used that perform a cytotoxic action (toxic for cells) against those cells that are rapidly proliferating. However, most drugs used do not distinguish cancer cells from healthy cells; for this reason their use is associated with numerous and important secondary effects, which mainly concern those tissues in which there is a rapid cellular turnover, such as hair, mucous membranes and blood.
Sometimes pre-operative chemotherapy is performed to try to reduce the size of the tumor mass that will have to be surgically removed.
- Radiotherapy : radiotherapy uses the use of high-power X-rays, which are directed and concentrated in the area where the cancer mass is present. As with chemotherapy, radiotherapy can also be performed before surgery to try to reduce the size of the tumor.
Another strategy used is that of internal radiotherapy (brachytherapy), which consists in placing a permanent source of radiation near or within the area to be treated.
In recent times, the technique of intraoperative radiotherapy has also taken hold, namely the concentration, during the operation, of a high dose of radiation, or to attack parts of tumors that cannot be surgically removed, or to bombard the area where the tumor is developed to avoid possible relapses.
- Hormone therapy : hormone treatment is mainly used in those tumors that are hormone-sensitive, such as breast and prostate cancer.
- Immunotherapy : this therapeutic strategy consists in the use of vaccines that are able to stimulate and direct the immune system against cancer cells. To date (April 2015), however, in Europe, such substances have not yet been approved; instead, antibody-based drugs are present that bind specifically to tumor target cells, facilitating the action of the immune system.
- Hyperthermia : it uses the use of heat to induce damage to neoplastic cells and increase the effectiveness of radiotherapy and chemotherapy. A generalized hyperthermia ("artificial fever") can also be used to stimulate the activity of the immune system against cancer cells.
- Palliative treatment : this treatment aims to reduce the symptoms caused by the tumor by reducing the physical, emotional and social discomfort of the cancer patient. Palliative care is therefore an approach that aims not to eradicate the pathology, but to make the individual feel better.
