Cancer is a disease characterized by abnormal cell proliferation and anomic in a normal tissue of the body. These cells are derived all of the same clone, initiator of the cancer cell that has acquired certain characteristics allowing them to divide indefinitely. During the course of the disease, some cells can migrate from their place of production and form metastases.
"Cancer" is a general term referring to any disease for which certain cells in the human body is divided in a way uncontrollably. The resulting new cells can form a malignant tumour (neoplasm) or spread throughout the body.
Major types of cancers
There are generally:
* Carcinomas: a cancer epithelium, ie a surface composed only of cells
* Sarcomas: proliferating cancer in tissues "support" as bones.
* The hematopoietic cancer: cancer of blood cells.
On the class according to the affected organs, such types of cancer:
* Breast cancer
* The colon cancer: cancer of the colon and, near the rectum
* Cancer of the pancreas
* The multiple myeloma cancer of the bone marrow
* Leukaemia: cancers of the blood
* Kaposi's sarcoma cancer of the blood vessels
* Lymphomas: Hodgkin's disease and non-Hodgkin's lymphoma.
* The testicular cancer
There are almost as many sources of cancer tissue in the body. Some are more frequent than others.
The oncology (cancer) is the medical specialty of study, diagnosis and treatment of cancers. It is practiced by doctors oncologists or cancer. These may be depending on their specialty chimiothérapeutes or radiation.
As a result of a negative image on the prognosis to the public, cancer has many synonyms used by doctors: malignancy, cancer, neoplasms, polymitose, carcinoma…
Some terms are more popular tumour, crab…
Some cancers have already been described in Egyptian writings to -3500. It Hippocrates who gave the first definition of the disease known as "carcinoma" or "squirre 'tumor (swelling) hard, non-inflammatory, which tend to recur and become widespread until death.
The comparison of national statistics is difficult because the detection and classifications have changed from time to time and countries. Thus, in France, the term "environmental causes" refers to chemicals and pollution…, then in English, it refers to everything that surrounds the man and, in general, all exogenous factors, ie the sun, alcohol, smoking, the number of pregnancies…
Quality of care: survival rates and mortality
The survival rate also depends on age. Five years after diagnosis, 70% of 15-45 years survive. While only 39.4% of cancer sufferers aged 75 years survive more than 5 years ... knowing that, given the risk of metastases, not talking about a cure for cancer, but remission (see further developments).
To estimate the effectiveness of screening and care, using the rate of survival and mortality at a certain time after diagnosis.
For a group of people in whom were diagnosed with cancer, one can distinguish those died as a result of their cancer, and died of something else. The mortality at a time t (for example, 10 years) linked to cancer is the probability of dying simply because of cancer during the time t after the diagnosis.
The problem of evaluating this mortality is that we should know the causes of all deaths of persons who have been diagnosed with cancer, which is impossible. It uses another estimate, for a group of persons of the same sex and similar age, using the "relative survival", ie the relationship between:
* The probability of survival after a time t the group of people who have been diagnosed with cancer, and
* The probability of survival t of a group of people without cancer, the same age and same sex.
The mortality is the complement to 1 of this relative survival.
Studies show a mortality of about 2% beyond 10 years after diagnosis in developed countries, pointing irrationality of segregation experienced by patients who have had cancer from the insurance and banking ( surcharges, refusal to loan…).
The following results are from the document Cancers - Forecasts long-term INSERM.
The Eurocare study examined some twenty European countries for cases diagnosed during three periods (the patients studied during a period form a "cohort"): 1978-1985, 1985-1989 and 1990-1994. This study does not distinguish the stage of diagnosis.
There are many factors that predispose to cancer: they are known carcinogens, or cancer-causing carcinogens. The study of these factors is called carcinogenesis.
They can be:
* Psychology: Since the progress of psychoanalysis and the psychosomatic, we know that many cancers are the result of a combination of mental illness often unconscious, which undermines the balance of the body. The links have been made between the psyche and the immune system can now say that most diseases are favoured by the psyche, so that psychotherapy or psychoanalysis can not only prevent but also to promote their healing.
* Genetic, ie have a hereditary component (case of some breast cancers);
o pollution: its exact role is difficult to specify;
o Food: Obesity promotes many cancers. Regular consumption of fruits and vegetables reduces the risk of many cancers. Alcohol, finally, promotes cancers of the throat, esophagus and liver;
o radiation (not to mention the role of the sun: it is therefore important to use sunscreen properly during prolonged exposure to sunlight because it increases the risk of skin cancer) because of ultraviolet;
o infections by some germs;
WHO estimates that 10% of the proportion of work-related cancers which corresponds to over 200 000 deaths a year (the role of asbestos such as mesothelioma).
It is worth noting the particular role of tobacco which is an important risk factor for various cancers (respiratory tract, ENT, bladder).
According to the latest report of the 2007 Faculty of Medicine, tobacco remains the leading cause of cancer. Then alcohol. Other causes are overweight and lack of exercise, then occupational exposures and hormonal treatment of menopause on women. Only 1% of deaths are related to pollution. Finally, 50% of the origins of cancer remain unexplained.
Genetics and cancer
The cancers are genetic diseases ie they are caused changes in the quantity and / or quality of our genes. As it is somatic genetic alterations that are present in the fabric sick, most cancers are not hereditary. The familial cancers (10% of human cancers) are associated with impaired constitutional (or germ) of a gene. This alteration is therefore present in every cell of our body, gametes included. It can be transmitted to offspring.
There are three main categories of genes associated with diseases cancer: oncogenes, tumor suppressor genes and genes for DNA repair.
1. The oncogenes (also called proto-oncogenes or c-onc) are positive regulators of cell proliferation. They become hyperactive and their modification is dominant because it suffices that one of two copies of the gene is altered. It currently has identified more than 100 oncogenes. The most famous are the genes Ha-ras, myc, or abl.
2. The second category includes tumor suppressor genes that are negative regulators of cell proliferation (the brakes). Both copies of these genes are inactivated in cancer.
3. The third category is the genes of many repair systems that can detect and repair DNA damage that have altered oncogenes or tumor suppressor genes. These repair systems are also inactivated in cancer cells.
The cell transformation
The cellular transformation corresponds to the passage of a eukaryotic cell normal to a cancerous state. Not to be confused with bacterial transformation which is something quite different.
Unlike genetic diseases like cystic fibrosis, muscular dystrophy or some hémophilies who are monogenic diseases (only one gene is usually altered), cancer is a multigenic disease. Each cancer has its origins alteration of 10 to 20 genes. These alterations occur successive ways, each of them favouring the following (see box). This continued deterioration usually occurs over a very long beach chronological (5 to 20 years). This suite of alteration is not random and for each type of cancer, has been highlighting i) some specific genes altered and ii) a chronology in the development of events in cancers of the colon, such succession d Events include (among others) first inactivation of tumor suppressor gene APC, then a mutation of Ha-ras oncogene followed by the inactivation of tumor suppressor gene p53. There are other events that remain to be identified. The essential point is the specificity of altered genes and their chronology. In another type of cancer, genes involved and the timing are totally different. APC is altered in cancers of the colon and never in skin cancers. By against the alteration of p53 is more ubiquitous and can be found in virtually all types of cancers. In skin cancer unlike colon cancer, alteration of the p53 gene is one of the first events. This great genetic diversity is the basis of the heterogeneity of cancer pathology. Within a particular type of cancers such as lung cancer, there are several subtypes (lung cancer-small cell adenocarcinoma, a major lung cancer cells, etc.) Each being associated with genetic alterations. The situation is similar for other cancers as breast, stomach or skin, each body can be linked to several types of cancers, depending on the type of histological cell that has been the cause of the disease.
Origin of cancers
Surroundings 15% of human cancers may be associated with infectious agents. This may be a virus (HBV and liver cancer, HPV and cancer of the cervix, and EBV Burkitt lymphoma), more rarely bacteria (Helicobacter and gastric cancer) or even more rarely parasites (Schistosomes and cancer liver). In all these cases, in addition to the infection, there are also alterations of oncogenes and suppressor genes in tumors. The infectious agent is involved as a step in the process of cell transformation.
The origin of alterations that change the oncogenes and suppressor genes is multiple. They are generally class into two broad categories, endogenous and exogenous.
1. The exogenous origin corresponds to all environmental exposures to which a body is subjected. This ranges from tobacco to ultraviolet sun through asbestos, gamma rays, alcohol and other substances to which an individual is exposed voluntarily or involuntarily. They may act directly in our DNA and cause damage to certain molecules in tobacco or ultraviolet or cause inflammatory statements encouraging the emergence of cancerous cells (alcohol).
2. Alterations of endogenous origin are caused in part by molecules from our metabolism as the reactive species in oxygen. Each day our DNA undergoes millions of aggression on the part of these molecules but in the vast majority of cases, they are repaired very efficiently. However, only one failure in the repair of a gene important to initiate or continue a process of cell transformation. Recent work (2007) suggest that systems of DNA repair have an efficiency decreases with age.
In 2000 R. Weinberg and D. Hanahan suggested that the cellular transformation through the acquisition of at least six properties:
1. Independence vis-à-vis signals stimulating proliferation. The normal cells do divide that when they receive a stimulus. The tumor cells no longer need this signal.
2. Insensitivity to signals inhibitors
3. Abolition of apoptosis or programmed cell death. In case of stress or trouble could not be eliminated, a normal cell commits suicide using apoptosis. The inactivated tumor cells have all these mechanisms to better survive.
4. Unlimited proliferative capacity: the usual number of cell divisions in a human cell is 50 to 60 (cellular senescence, Hayflick limit), after which it ceases to be able to divide (see article Telomere). The tumor cells continue to divide without limit visible through the activity of telomerase, which is highly active in all cancer cells.
5. Ability to generate angiogenesis. The tumor cells (tumor) have a strong need oxygen to survive. They will therefore stimulate the formation of new blood vessels to the tumor fresh air.
6. Acquisition of a power-invasive. The tumor cells are capable of moving inside a blood vessel to be transported to another body or they will generate a second tumor (metastasis)
Even if there are elements to identify a cancer with high probability, the diagnosis of certainty that does analysis on the microscope (anatomopathologie) a sample of the tumor (possibly helped by other techniques). This sample is just a biopsy (taking a simple piece of the tumor), which can be made, depending on the location, following different procedures (fibroscopy, puncture through the skin…) or a surgical (tumour removed by the surgeon).
From its initial focus on cancer will (in addition to any treatment or if the treatment is not effective):
* Develop locally. It causes in this case a compression bodies neighbors, even flooding and destruction of surrounding tissue;
* Develop a regional basis. It invades the lymph nodes, where house immune system cells;
* Distance spread of the tumour and form metastases. There is often confusion among patients and their families: a breast cancer metastases in the brain does not give a brain cancer, is always the initial breast cancer, but that has developed elsewhere. We must continue to treat it as breast cancer.
The evolution depends on the type of cancer and its care: some are only very few metastases and are very sensitive to treatment can result in the vast majority of cases a complete remission and prolonged (this term remission is specific to cancer and healing differs by the lack of certainty about a relapse in the short, medium or long term). Others are still very difficult to control and can cause death in the short term. An accurate assessment of the type of cancer from a doctor who specializes is therefore indispensable.
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