Expression of CD44 isoforms has been investigated on normal breasts, fibroadenomas, cysts and breast cancers. Carcinomas express additional variants in comparison with normal breasts while fibroadenomas and cysts do not. Invasive cancers also express more variants than in situ carcinomas. Recent studies tend to demonstrate that overexpression of CD44 is not a survival prognostic factor whereas expression of exon 2v and/or 3v could be. Results for exons 4v to 10v are presently conflicting. Further studies will then be necessary to clarify the role of CD44 isoforms in mammary carcinogenesis and metastasis. Metastatic capacity could be linked with expression of additional variants but also with no transcription of variants associating exon 6v with either exon 10v or both exons 9 and 10v.