It is the uncontrolled and autonomous cell proliferation. In general there is a loss or reduction in cell differentiation as a result of alterations in genes that regulate growth and differentiation . Recalling, when the cell loses specialization, there is an increase of proliferation.

Many people use the term tumor to refer to neoplasm, but the term tumor is referred to mass effect. Thus , the tumor is synonymous with anything which may accumulate and lead to the enlargement of the organ . Not all tumor is neoplastic , then the word must not be used to refer to neoplasms. So there are non-neoplastic tumors (the ones of the five cardinal signs of inflammation) and neoplastic ones.

According to the clinical behavior of the tumors, they are classified into benign and malignant . Therefore, there are different nomenclatures to differentiate this behavioral change .

Benign mesenchymal neoplasms are named using the prefix from the source cell with the suffix OMA , so a benign mesenchymal neoplasm of cartilage tissue is called chondroma , for example. If it is an epithelial benign one , the nomenclature is according to the architecture that is being formed , ie , adenomas ( form glandular structures ) , papillomas ( form surfaces with fingerlike projections - papillae ) and cystadenoma ( cyst formation ) .

Mesenchymal malignant neoplasms are named using the prefix of the source cell with suffix SARCOMA , then a malignant mesenchymal neoplasm of cartilage is called chondrosarcoma, for example. If it is  andepithelial malignant one, the suffix used is CARCINOMA and, thus, the most common is adenocarcinoma .

Characterizing and distinguishing the two neoplasms, benign growth is expansive in low speed, they have pseudocapsule and have few typical mitosis, they do not invade the blood vessels and do not cause metastasis, therefore they cause no hemorrhage and necrosis. Meanwhile , the malignant has fast infiltrative growth without pseudocapsule , typical and atypical mitosis and, frequently, invade vessels , causing metastasis and, thus , hemorrhage and necrosis .

If the malignant are able to invade vessels and cause metastasis , it is correct to say that only malignants are able to disseminate and deploy remotely. This can be spread by three routes: hematogenous ( in which the neoplastic tumor invades blood vessels and makes its implementation in another region ) , lymphatic (in which malignant neoplasm invades the lymphatic vessels and migrate to another area ) and by ducts (in which the spread is by ducts such as the bile duct ) .

Clinically, neoplastic tumors are classified in TNM ( Tumor, Node and Metastasis ) . This classification system is the most used inclassification of malignant tumors and the description of its anatomical extent . Basically , the TNM system is based on the evaluation of three components : T - primary tumor extension N - the absence or presence and extention of metastasis in regionais lymph nodes M - the absence or presence of metastasis. They adding numbers to these three components to indicate the extention of malignant disease . Thus we have:
T0, T1 , T2 , T3, T4 | N0, N1, N2 , N3 | M0, M1

Molecular basis

Environmental agents (viruses , radiation) damage the DNA and the genome not repair , genetic mutations occur by activating proto -oncogenes and inactivating suppressor genes . These proto - oncogenes activate cell growth , while tumor suppressor genes are inactivated . This inability to repair DNA damage can also occur by genetic mutations in addition to environmental agents . Along with this , there are changes in genes that regulate apoptosis . From the activation of proto - oncogenes , inactivation of suppressor genes and alteration in genes that regulate apoptosis, there is uncontrolled cell proliferation and decreased of apoptosis . A clonal expansion of those cells happens and, now, they are able to evade the immune system. Those cells suffer additional mutations leading to tumor progression. So it is a malignancy with invasion and metastasis .

These affected cells undergo some stages :
1 - initiation phase : the first stage of carcinogenesis , where cells undergo the effect of carcinogens that cause changes in some of their genes .
2 - promotion phase : the second stage of carcinogenesis , where the cell started to be transformed into a malignant cell , slowly and gradually.
3 - phase progression : it is the third and final stage and is characterized by uncontrolled and irreversible multiplication of abnormal cells; in this stage the cancer is already installed , progressing until the appearance of the first clinical manifestations of the disease .