Objective: Breast cancer is the most common cancer in women and in cancer-related deaths, it is extremely important to determine the clinical course of the disease. Cyclin D1, an important regulator of the cell cycle, and TIL, which are important in immunotherapy, are becoming the focus of cancer research. The aim of the present study is to detect the expression of cyclin D1 and TIL rations in breast cancer, and to analyze its relationship to the clinicopathological parameters. We aim to predict prognosis using these parameters.

Material and Method: We evaluated 90 cases diagnosed with invasive breast carcinoma, who came to our laboratory between 2014 and 2020. Cyclin D1 expression was assessed immunohistochemically and TIL was evaluated morphologically.

Results: There was no statistically significant relationship between cyclin D1 expression and histological subtype, tumor size, lymphovascular inva-sion, metastatic lymph node number, extracapsular infiltration, HER2 status, Ki-67 expression, T and N stage. The expression of cyclin D1 was negatively correlated to histological grades and nuclear grades. Histological and nuclear grades were found to be lower in patients with high cyclin D1 expression. The expression of cyclin D1 was significantly correlated to ER and PR. Luminal groups showed statistically significantly more cyclin D1 expression. Histological and nuclear grades were significantly higher in cases with high TIL scores.

Conclusion: Cyclin D1 expression and TIL score are associated with some known good prognostic factors. This suggests that cyclin D1 expression and TIL score have value as good prognostic parameters.