Stable cells, also known as cell lines, are homogeneous populations of cells selected and cultivated in the laboratory for their ability to divide indefinitely. Unlike primary cells, these cell lines have the potential for unlimited division and are often derived from tumour cells. They are used in a variety of cellular and molecular biology research applications. Stable cell lines are a valuable tool for studying the cellular and molecular mechanisms involved in various biological processes, as well as for testing the efficacy of new drugs. They are also used to model the behaviour of cells in vivo and to understand the processes of neoplastic transformation. The characteristics of cultured cells are the result of their origin and their ability to adapt to culture conditions. Stable cell lines are widely used in biomedical research to study the effects of new drugs, cosmetics and chemicals, as well as to understand disease mechanisms and develop new therapies, and they are used as controls in research experiments to compare the results obtained with abnormal or modified cells.