Despite the large availability of medical information on the Internet, health consumers still encounter problems to find, interpret and understand this information. These problems are mainly due to their lack in medical knowledge and the difference between their language and the language of health professionals. In order to propose information retrieval services more adapted to health consumers language and knowledge, we have developed techniques to collect, identify and analyze the terms and the expressions used by lay persons to talk about breast cancer. The study of health consumers' language is a relatively recent research field. Many studies have been conducted to analyze and characterize the vocabulary used by health consumers to talk about medical subjects in English. We have conducted the same study for the French language in the breast cancer field. We have gathered a corpus of texts to identify terms and expressions used by health consumers who talk about breast cancer in French. The terms have been organized in a concept-based terminology. This terminology has been analyzed on several levels: concept level, term level, term-concept level and finally relation level.