**2.1.1 The different cell lines and their main properties**

Significant amounts of data on breast cancer have been collected over the past 40 years, thanks to the use of established cell lines. The first breast cancer cell lines (BCCL) have been established in the sixties-seventies and very few new cell lines have been developed since. Only a hundred of BCCL are currently available and three of them have been extensively studied and represent now nearly 80% of the 35 000 publications mentioning breast cancer cell lines (Lacroix & Leclercq 2004).

Most of the cell lines were created from cells derived from metastasis or from pleural effusion. Pleural effusions contain large amounts of well isolated tumour cells and few contaminating cells such as fibroblasts, thus making their recovery and growing easier than those of cells directly derived from primary tumours or metastasis. Moreover, metastatic cells are highly dedifferentiated cells, which allow their cultivation more successfully than the primary tumour cells.

The three more used BCCL (MCF-7, MDA-MB-231 and T47D) are issued from pleural effusion of an invasive ductal carcinoma (Soule *et al.* 1973; Cailleau *et al.* 1974; Keydar *et al.* 1979), and they mainly differ by their oestrogen receptor (ER) and progesterone receptor (PgR) status: MCF-7 and T47D are ER+ PgR+ while MDA-MB-231 is ER- PgR-. Among these three cell lines, MCF-7 was the most often used during the last ten years: it has been cited in 53% of all the scientific papers mentioning BCCL, while MDA-MB-231 and T47D were respectively cited in about 18% and 7% of these articles (calculation made on the basis of a Medline-based survey in March 2011).

The use of these lines has many technical advantages.


These advantages have allowed to gather essential data for the study of breast cancer in the last 40 years, making these cell lines reference models in the field with the establishment of a complete genetic and proteinic profile.

### **2.1.2 The main drawbacks of these models**
