Objective: Breast cancer is common, especially in older women. It is also one of the leading causes of cancer-related deaths in young women. Survey in young women is shorter and the response to medical treatment is lower, because cancer cases in this group of patients are considered as differences in hormone receptors in cancer cells, unlike those seen in other age groups. The aim of our study is to evaluate the clinical, histopathological features, and hormone receptors of breast cancer in women under the age of 40, and to create datasets to develop different methods in medical treatments to be applied to patients of this age. Material and Methods: Localization, tumor size, histological grade, lymph node involvement, multifocality/multicentricity, distant organ metastasis, hormone receptor (Estrogen-ER, progesterone-PR) status, HER2 and ki-67 proliferation markers were retrospectively analyzed in 72 invasive breast carcinoma cases under the age of 40 diagnosed in the pathology clinic of our hospital. Results: The average age of the patients is 35.31 and 59.7 % of them are localized in the right breast. Ductal carcinoma is the most common histological type, and high grade was detected in 52.8 % of cases. The majority of cases were ER (87.5%) and PR (73.6 %) positive, HER2 (83.3 %) negative. Ki-67 proliferation index was observed at a high rate in 52.8 %. Conclusion: These findings show that breast cancer tumors observed in young women have higher histological grade and high proliferation index. Therefore, it shows that cancers seen in this age group will progress more biologically and the prognosis will be poor.