[Breast cancer in young women. Histological and prognostic specificities: how are they different from older women?].

Early-onset of breast cancer (under the age of 40) represents only 7% of all breast cancers, but is the most common cancer in this age group in women. It is also known to be of worse prognosis, with a more aggressive tumoral behavior. The interaction of different prognostic factors contributes to the complexity of this population: tumor burden and biological features (using classical histopronostic features and genomic data) show differences from older women. Nevertheless, the prognostic impact of age varies according to the histological subtypes and seems pejorative mainly for the luminal subtype, probably with a crucial role of the hormonal environment and the treatments targeting the endocrine sensitivity of these tumors. In other subtypes, the influence of young age appears to be less significant, especially in HER2+ breast cancers.