**2.1.3 Non cancerous immortalised cells as controls**

It should be noticed that the study of mammary tumours also involves the use of non cancerous cells which were immortalised. These cell lines were derived from healthy breast tissue, but only few models, obtained by different methods, are available.


 Under chemical pressure, normal cells in culture can also be immortalised. This is the case for some cell lines as 184A1 and 184B5 which were obtained by exposition to benzo[a]pyrène, a chemical carcinogen, leading to clonal events which are the origin of these immortal cell lines (Stampfer 1989).

The use of these "non cancerous" cell lines is important to give a comparison point to results obtained with cancerous cell lines. However, there are drawbacks and controversy to their use, the major one concerning the way they were obtained. Indeed, if they are still nontumourigenic, they suffer of genetic modifications which lead them to become immortal. They are looking like normal cells, but they are not.
