Tumor

This is a derivative of altered, unregulated, unrestrictedly proliferating organism cells. There are more processes in the body characterized by cell proliferation (e.g., regeneration, hyperplasia), but they differ from tumors in several essential features. These processes are the body’s reaction to certain causes, which, once removed, stop the processes. Moreover, they are regulated by the body’s general systems: humoral mechanisms, the nervous system, etc. Meanwhile, the cause of tumor formation is often unclear. Once formed, it does not stop growing and spreading, regardless of whether the causative factor is still active or not. Clinically, tumors are classified as malignant and benign (or non-malignant). This classification is determined by the characteristics of the cells constituting the tumors, their growth nature, and their impact on the body. Benign tumors usually grow slowly, pushing aside surrounding tissues, but do not spread to other organs and do not regrow after surgical removal. Their cells are monomorphic, not much different from normal tissue cells, but they form unusual structures for the latter: growths, nodules. A benign tumor is confined, often encapsulated. Malignant tumors usually grow faster than benign ones, invade surrounding healthy tissues, corrode and destroy them. Furthermore, cells of a malignant tumor can detach from the initial clone and travel to distant organs, spreading throughout the body – metastasizing. Surgically removed malignant tumors can regrow. Cells of a malignant tumor are atypical, often polymorphic, anaplastic, with many mitoses, sometimes completely dissimilar to the tissue from which they originated. The boundaries of a malignant tumor are unclear. There are also tumors that share many characteristics with benign ones but as they grow, they destroy surrounding tissues. These are semi-malignant tumors. They grow slowly, can slightly invade surrounding tissues, but do not spread to distant tissues. Surgically removed tumors of this type can regrow. Cells of this tumor are anaplastic, can be polymorphic, with mitoses. The tumor is usually confined. There are no strict boundaries between groups of benign and malignant tumors. Some benign tumors can turn malignant (become malignant). Moreover, the clinical course of morphologically differentiated, mature tumors can sometimes be malignant. For example, benign tumors of the brain and internal secretion glands significantly disrupt the body’s functions. Malignant tumors are further classified based on the type of cells from which they developed. For example, carcinoma grows from epithelial cells, sarcoma originates from mesenchymal tissue cells. Carcinomas account for the majority (about 90%) of adult human tumors. The name of malignant tumors – carcinomas and sarcomas – usually includes the name of the organ where the tumor grows and describes the histological form of the tumor. Therefore, the name of the tumor reflects three main elements: the tumor’s histogenesis, histological structure, and the affected organ.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė