What is Cancer?
With the term cancer (or malignant tumor) indicates a group of pathologies characterized by uncontrolled cell replication and diffusion.
In addition to increasing its number of cancer cells, a malignant growth has the ability to infiltrate and destroy nearby healthy structures. The relatively rapid growth rate and the ability to originate distant growths (metastases) by blood or lymphatic diffusion of cancer cells also contribute to determining its malignancy. All this distinguishes a cancer from a benign tumor, which has a tendentially slow growth and confined to the site of origin; however, it should be noted that, with the passage of time, some types of benign tumors can evolve into malignant neoplasms.
The terms malignant tumor, cancer and malignant neoplasm are to be considered synonymous.
Normal and uncontrolled cell growth
Cancer cells lose the structure and function of the cells of the healthy tissue from which they derive due to their inability to differentiate properly.
In normal tissues, cells reproduce to meet the various needs of the organism, such as the growth or replacement of dead or damaged cells. In these tissues, cell proliferation and differentiation are subjected to strict biochemical control. Cells, in fact, they divide controlled by various growth stimuli and are equipped with defense mechanisms capable of slowing down the development processes, allowing to repair any anomalies; if this does not happen, the cell undergoes a programmed death process defined apoptosis.
The image shows a possible process of carcinogenesis: the transformation of normal cells into cancerous cells is the result of a series of mutations. In cancer, all these regulatory processes are compromised and cancer cells reproduce in an uncontrolled manner by evading the above defense mechanisms. At the origin of this phenomenon there are several genetic alterations which, when added to each other, cause the control mechanisms already mentioned to blow up. It is therefore not sufficient for a single regulation mechanism to be defective, but errors must develop. on several fronts, in particular, these alterations lead to an "aberration" in the expression of proto-oncogenic genes.
A proto-oncogen is a gene physiologically involved 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 at this point will cancer develop. Oncogenetic genes are in fact able to overexpress or under-express proteins that regulate some biochemical growth processes, causing preferential and accelerated cell growth.
In the same way, cancer can also result from the inhibition of tumor suppressor genes; these genes, called tumor suppressors, code for proteins that protect the cell from the accumulation of potentially tumor mutations.
Once triggered, uncontrolled cell growth can lead to invasion of surrounding tissues and, often, also to invasion of tissues that are far from the site of origin (through 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 malignant neoplasm); in the benign tumor, however, the cells substantially maintain the same structure and function as the normal cells of the tissue from which they originate. Furthermore, although it also proliferates autonomously, a benign tumor expands without penetrating the surrounding tissues and does not undergo metastasis.
Classification and nomenclature
Mutated cells can evolve into various types of cancer, each with its own etiology.
The different types of cancer can be classified according to three parameters:
- Histology of the affected proliferating cells;
- Aggression and expected clinical course (for both malignant and benign tumors);
- Tumor staging (for malignant tumors only).
The nomenclature of tumors is based on the type of tissue of origin, for example: carcinoma (originating from epithelial tissue), sarcoma (originating from muscle or connective tissues), melanoma (originating from melanocytes), leukemia and lymphoma (respectively of haematological origin or lymphatic).
Signs and symptoms
From the moment it begins to develop, the cancer grows very rapidly and exponentially but, despite this, it initially produces no symptoms. The first signs begin to appear only when the cancerous mass reaches a certain size.
Furthermore, the first symptoms that appear are often non-specific, in the sense that they can also be caused by diseases other than cancer.
There are more than 100 different types of cancer that affect humans and the clinical manifestations of each vary considerably, making it difficult to produce a definitive list of all possible signs and symptoms. In this regard, the American Cancer Society has published those that are the main warning signs for early cancer detection. It is very important, in fact, that patients learn to recognize warning signs in these symptoms that deserve immediate investigation, since cancer is more 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;
- Noticeable paleness and loss of energy
- Change of habits in going to the body and urinating;
- Unusual discharge or bleeding
- Thickening or lump in the breast or elsewhere
- Indigestion and difficulty swallowing
- Obvious changes in warts or moles
- Nagging cough or change in tone of voice.
In the moment in which unusual symptoms are found it is advisable to consult a doctor.
Causes
It is very difficult to pinpoint what triggers cancer in 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 nature, which contribute to each other in the development of the disease.
Environmental factors
This category does not only include factors affecting 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 his or her lifestyle. life.
- Air pollution: some studies have shown that in subjects who breathe polluted air for many years, the risk of contracting cancer increases; in particular, an increase in cancer mortality has been shown, 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 defined mutagenic; for this characteristic, many of these substances can also cause cancer and are called for this carcinogenic. Epidemiological studies have shown that certain types of cancer are found above all in some classes of workers. The best known example is perhaps that of cancer of the lungs and pleura (the membrane that covers them) due to exposure to and inhalation of asbestos fibers (otherwise known as asbestos). Similarly, people exposed to substances such as hexavalent chromium, nickel and tar are subject to an increased risk of developing lung cancer.
Benzene, a very common organic solvent that is also found inside cigarettes, favors the onset of leukemia.
Polycyclic aromatic hydrocarbons are substances found inside fossil coal and oil; they are present in the exhaust gases of cars and also derive from the combustion of wood and fossil fuels; exposure to these compounds favors the onset of cancer to the bladder. - Ionizing radiations: ionizing radiations are generated following nuclear reactions of both artificial and natural origin (such as those occurring on the surface of the sun). These radiations are able to penetrate the matter and hit the molecules contained inside the cells. When the genetic material is affected, this can break down leading to the deactivation of one or more of the affected genes, to the elimination of part of the DNA sequences and mutations of various kinds. If the damage is quite substantial, in general, cell death occurs; 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 (tumor suppressor genes that are able to to control oncogenes by stopping uncontrolled cell growth).
- X-ray: these radiations are used in diagnostic and therapeutic medical fields. The risk of developing cancer when exposed to this type of radiation tends to accumulate with dose.
- Ultraviolet rays: these rays, generated by the sun, are useful to the body, as they are necessary for the production of vitamin D; however, exposure to the sun in the middle of the day damages the skin, increasing the risk of incurring skin cancers; sunburn in particular increases the risk of contracting melanoma.
- Lifestyle: the lifestyle of each individual greatly affects the risk of incurring neoplastic pathologies. Tobacco smoke appears to be the most important risk factor; this, in fact, is not only able to induce mutations in tumor suppressor genes, but favors the development of the tumor once these have already occurred; it also has a negative action on the immune system, depressing it. It has been shown that smoking causes more than 90% of lung cancers and also other cancers, including that of the oral cavity, larynx, esophagus, bladder , kidney, pancreas, colon, stomach and breast.
The excessive consumption of alcoholic beverages is also able to favor the onset of cancer; recent studies have shown that cancer caused by alcohol is not only found in subjects who abuse it, but also in subjects who drink it moderately. cancers that can be caused by alcohol are that of the mouth, esophagus, larynx and pharynx, colon and breast. - Diet: nutrition plays a fundamental role in the risk of contracting cancer; it has in fact been shown that a diet rich in salt, animal proteins and fats, and low in vegetable fiber, vitamins and minerals, greatly increases the risk of developing some Although there is not enough evidence to indicate 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 cancers. An improper diet can also lead to overweight and obesity; in this regard, there seems to be a relationship between this pathology and the onset of colon, endometrial, breast and gallbladder cancer.
- 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 people of normal weight. Various studies have shown that increasing the frequency and intensity of exercise can decrease the chances of getting breast, uterus and bowel cancer.
Infectious factors
Infectious agents capable of causing cancer include 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 oncovirus. The best known are the Papilloma virus (cause of the cervical cancer), L"Human herpesvirus 8 (cause of the Kaposi's sarcoma), i hepatitis B and C virus (cause of the HCC) and the Epstein Barr virus (which usually causes mononucleosis, but in Africa it is responsible for the onset of Burkitt's lymphoma).
The bacterium Helycobacter pylori - usually responsible for gastritis and gastric ulcers - it can be easily eradicated, but it seems to be involved in the onset of some stomach tumors.
HERITAGE factors
In fact, when it comes to cancer, it is more correct to speak of "familiarity" than of hereditary factors. The disease, in fact, is not transmitted from one generation to the other through genes; what is instead transmitted is the greater predisposition to develop the disease. Cells containing mutated genes can therefore be inherited that facilitate the onset of cancer, but it is necessary that more errors occur and add up, on several fronts, to arrive at the development of the tumor.
Despite the large number of factors that contribute to the development of cancer, more than 30% of cancers can be avoided by reducing the main risk factors.
Many cancer deaths could be avoided by quitting smoking, leading 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 patient's condition.
The main types of treatment used are:
- Surgery: surgical treatment is the most used to remove solid type 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 cell division that characterizes tumors. Drugs are used that exert a cytotoxic action (toxic to cells) against those cells that are rapidly proliferating. However, most of the drugs used do not distinguish cancerous cells from healthy ones; for this reason their use is associated to numerous and important secondary effects, which mainly affect those tissues in which there is a rapid cell turnover, such as hair, mucous membranes and blood.
Sometimes a pre-operative chemotherapy to try to reduce the size of the tumor mass that will have to be surgically removed. - Radiotherapy: radiotherapy exploits the use of high-power X-rays, which are directed and concentrated in the area where the cancerous mass is present. As for chemotherapy, radiotherapy can also be performed before surgery to try to reduce the tumor size.
Another strategy used is that of internal radiotherapy (brachytherapy), which consists in placing a permanent source of radiation near or inside the area to be treated.
In recent times, the technique of intraoperative radiotherapy, ie the concentration, during the operation, of a high dose of radiation, either to attack parts of the tumor that cannot be removed surgically, or to bomb the area where the tumor has developed to avoid possible recurrence. - 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 target the immune system against cancer cells. To date (April 2015), however, in Europe, no substances of this type have yet been approved; instead there are drugs based on antibodies that bind specifically to tumor target cells, facilitating the action of the immune system.
- Hyperthermia: exploits 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 decrease the symptoms caused by the tumor by reducing the physical, emotional and social distress of the patient with cancer. Palliative care is therefore an approach that aims not to eradicate the pathology, but to make the individual feel better.
