The invention relates to a method for the diagnosis and/or prognosis of breast cancer, by determining the expression level of transcription factor Snail 1 in a biological sample isolated from a subject and comparing the results obtained to reference values. The invention relates to the use of Snail1 interference oligonucleotides in the preparation of a drug intended for the treatment of breast cancer as well as pharmaceutical compositions based on a therapeutically effective quantity of said oligonucleotides.