In Algeria, breast cancer is currently the most common malignant tumor and the leading cause of cancer mortality in women. It’s a complex and heterogeneous disease. It’s histological, phenotypic, and molecular. It remains a poorly known disease, and current clinical and histological classifications do not fully predict prognostic and predictive treatment response parameters, which is a source of inappropriate treatment.The study involved 382 patients with infiltrating carcinoma. The age ranges from 20 to 89 years (mean: 49 years). The histological types identified are ductal carcinoma infiltrating CCI (78.49%) and lobular carcinoma infiltrating CLI (21.50%). Of the 382 patients, 90 are young women under 40 years of age or 30.41%, (mean age: 31 years) with 79.45% CCI and 20.54% CLI.The objective of our study is to perform an analysis of the clinical characteristics, histopathology in young women under 40 years of age by specifying their relative proportion and biological characteristics compared to all cases of all ages combined.The determination of the expression antigen Ki67, nuclear hormonal receptors RE, RP and HER2 Oncoprotein at the level of the infiltrating component is carried out by the technical immunohistochemistry IHC.Characteristics of carcinomas in young women under 40 compared to all patients in our series: pT3 tumor size: 24.63% versus 18.68%; histopronostic grade SBR III: 78.37% versus 72.01%; presence of ganglionic invasion pN+: 76,74% versus 75.75%; high mitotic index Ki67: 41.02% versus 14.84%; absence of expression of the hormonal receptors: estrogenic receptors RE- 71.62% versus 64.92%, progesterone receptors RP- 81.08% versus 78.15%; 31.25% HER2 oncoprotein expression versus 27.24%.The analysis of the results shows that tumors in young women are aggressive and have poor prognosis: large tumors and high histopronotic grade with significant mitotic activity and dominant ganglionic invasion.