Environmental Influences on Tumor Development and Spread Essay

Environmental Influences on Tumor Development and Spread - Essay Example Basic characteristic of malignant tumors is the abnormality in the cells, which is expressed through a decreased control of growth and functions, causing fatal diseases in the patients with invasive growth and metastasis. The division of tumors is based on the following criteria: histogenesis of the tumors, histologic image, biological activities of the tumor, eponyms and anatomy of the tumors (Abeloff et al.). According to their histogenesis, tumors are classified as epithelial and mesenhimal. However, such classification is incomplete, as certain tumors' origins is hard to indentify, such as melanomas and ovarian tumors, or cells which usually are not fond in the adult organism, such as embryonic tumors. The histologic image divides the tumors into a strong, middle or weak differentiation, depending on the maturity of the cells. If there is a complete loss of identity of the tumor in relation to the tissue that the tumor is generated from, we call that undifferentiated and anaplastic. The most important and familiar division of tumors is according to their biological activities. They are divided into benign and malignant; benign tumor cells are very similar to the cells of the tissue they originate from and they are very well differentiated. They grow slowly with expansion and the tumor is usually encapsulated. Malignant tumors have non-differentiated cells and are characterized with progressive growth and infiltration in surrounding tissue. In time, malignant cells enter into the blood and lymph vessels and through them they arrive to other parts of the organism where they cause metastasis or secondary growth.(Jovanovski et al.) There are tumors with semi-malignant behavior, which are usually represent locally malignant. In this group of tumors a localized growth is emphasized, while foreign metastasis appear extremely rare. Some tumors are named according to the authors that described them, for example Wilmsov, Hodgkin lymphoma, Brenner and other. Other tumors are named according to the organ, and not according to the tissue from which the originate, for example, hepatoma. The development of malignancy Malignant tumors can develop from any other tissue or organ, at any age. Before analysis of the growth and spread of the malignant tumors, a review of cell kinetics is necessary, in particular, division of the cells. All human cells which are capable to divide (bone marrow, gastrointestinal tract) enter in a cell cycle, which consists of 4 phases: G0 or resting phase, when the cells do not proliferate; G1 or intermittent before the DNA synthetic phase (last from 12 hours to several days); S phase or synthesis of DNA which lasts from 2 to 4 hours; G2 phase or phase after DNA synthesis, which lasts 2 to 4 days, and the cells have a tetraploid amount of DNA; and M1 phase or mitosis, which lasts from 1 to 2 hours (Abeloff et al). The new daughter-cells either enter in a G0 phase or begin a new cell cycle. Primary malignant tumors will arise with malignant change of one or more cells during suitable conditions. Cells that enter into a continuous division will create several cells that gather and create a primary tumor mass. Malignant cells usually have a cycle that last for several days. Generational time is the time necessary for a malignant cell to enter into a cell cycle and to create two