Abstract:Background: Actually, Breast cancer constitutes one of the most health problems in Algeria, and the leading cause of death among Algerian women. Breast cancer in young women is a rare form, but it has an aggressive behavior associated with a poor prognosis. Aims: this study focuses to report breast cancers phenotype in Algerian younger women. Material and methods: In order to better understand the determinants and tumor biology may explain earlier onset and aggressive breast cancers characteristics in Algeria from December 2011 to July 2014, 135 patients aged 40 years and under diagnosed with breast cancer were included in the study. Results: One hundred thirty-five women recorded, 65.9% patients were aged between 36-40 years. The mean age was 36.29 years. A significantly higher proportion of women were overweight or obese (62.9%). 75.6% patientshad full-term pregnancy. 29.6% breast cancers were diagnosed during pregnancy or after childbirth. 34.1% patients had a family history. In 87.4% of cases the revealing sign was nodule self-examination. Stage II and III associated with nodal extension, higher pathological grade, HR positive, were predominant. Neo-adjuvant was administered to 17.8%. 74.1%patients underwent radical mastectomy using Patey technique with complete axillary dissection.40.7% patients had distal metastases after diagnosis. The mean clinical tumor size was 4.88 cm.71.1% of tumors were invasive ductal carcinoma.69.9% patients had no family history. Conclusion: Breast tumors among Algerian young women are advanced with poor prognosis.