The tumor , also known as neoplasia or cancer , is a new formation of tissue-type independent, progressive and irreversible. The tumors are composed of cells that lose the ability to control proliferation, no longer responding to inhibition by contact with other cells.
The tumor may be benign or malignant.
The benign tumors are masses of cells well demarcated, surrounded by a capsule of connective tissue, unable to infiltrate the surrounding tissues or metastasize, and are generally well differentiated.
The malignant tumors are distinguished from benign tumors based only on the ability to infiltrate other tissues and form metastases, or of leaving the site of origin (through the blood vessels, the lymphatic system or by simple diffusion cross orientation the body cavity) to develop tumors in other tissues.
The majority of malignant tumors originate from the evolution of benign tumors, which acquire the ability to infiltrate the tissues and metastasize.
Nomenclature of tumors
The benign tumors are characterized by the suffix -oma (osteoma, fibroma, etc.) If the tumor is of glandular origin, then we use the term adenoma followed by cell type (prostate adenoma, liver, pituitary, etc.). The polyp, papilloma and cysts are benign tumors that originate from the epithelia.
The malignant tumors are characterized with the suffix sarcoma if they affect the bone tissue and cartilage (osteosarcoma, fibrosarcoma), the other uses the term carcinomafollowed by tissue. The tumors of glandular origin are called adenocarcinomas (lung adenocarcinoma, pancreatic, etc.).
Classification of tumors
The classification of tumors is performed by evaluating the grading and staging.
The gradation is a parameter of malignancy: is evaluated proliferative activity of cells, giving a value from 1 to 3.
The staging is a parameter of invasiveness: the magnitude is evaluated from the minimum detectable size (T parameter, from 1 to 4); the invasion of the lymph nodes (N, from 0 to 2), and the presence or absence of metastases ( M, from 0 to 2).
Genetic origin of cancer
The tumor has always monoclonal origin, or develops from a single cell which, exposed to a mutagenic agent, undergoes an irreversible damage of their DNA. The tumor does not develop in a single phase, it typically takes thousands of mutations that hit the genes responsible for the control of certain cellular functions. The main genes involved in tumor formation are of two types:
- the tumor suppressor genes . The cell is able to repair DNA damage, and does so using specific genes called tumor suppressor precisely because it can block the formation of a tumor cell. If these genes are mutated and the cell is no longer able to defend against attacks to the DNA, they increase the probability of formation of a tumor cell.
- genes or proto-oncogenes . These are the genes that control cell proliferation, that are normally turned on and off according to well-defined proliferative stimuli. If this control is less due to a gene mutation, the cell begins to proliferate without control. These genes are called proto-oncogenes because favorisono actively tumor formation.
Currently have identified several genes that are mutated in most cancers.
The tumors are not formed overnight, but with a process of progressive genetic transformation, where mutations accumulate over time and gradually transform the cell.Research has shown that no tumors formed by the mutation of a single gene, but almost always as a result of multiple changes involving the activation of several genes oncogenes and loss of tumor suppressor genes more.
How do you form a tumor
For a cell to be transformed into a cancer cell must undergo two processes: initiation and promotion.
The ' initiation is the mutation of DNA by a carcinogen. In general it is not sufficient that a substance is able to pose an mutations, as there are mutagenic substances, but only some of which are carcinogenic, or can transform the cell into a tumor. The damage caused by substances initiator is linear and does not have a threshold: if 1 g of substance X causes Y damage, cause damage 2Y 2 g, 3 g 3Y damage etc.. Furthermore, the damage is irreversible and has memory, ie the promotion can also act at a distance of time with respect to promozionel, causing the tumor.
The promotion takes place upon exposure of the cell to the agent initiator and is necessary in order to transform a normal cell into a tumor. The promoters are not carcinogenic agents alone, but must act after exposure to a carcinogen initiator, have an action that may be reversible in the early stages, do not form bonds with biological macromolecules and therefore do not produce mutations.
If the promoting agent is able to act for a sufficient time with a sufficient dose, will form the real tumor, which, however, can still be benign, not able to infiltrate and form metastases.Following further mutations, benign tumors can become malignant.
The substances promoters have, unlike those initiators, a threshold effect. Alcohol, a typical substance promoter, the promoter has no effect at low doses, but when intake reaches a threshold quantitative takes effect promoter. A promoter is a substance capable of increasing the proliferation of initiated cells, an effect that may contribute to the development of additional mutations and processing on the neoplastic cells.
There are carcinogenic substances which possess the ability initiator and promoter, thus able to induce tumor regardless of the presence of other substances.
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