Background & Objective:Breast cancer is one of the most common cancers in the world. There are some different types of breast cancer and triple-negative breast cancer is the type in which no receptors for estrogen, progesterone, and human epidermal growth factor receptor-2 are expressed. Identifying factors that can facilitate the diagnosis of triple-negative breast cancer is important. In this study, we decided to investigate the expression of GATA3 and GCDFP15 genes in triple-negative breast cancers.Methods:This is a retrospective descriptive-analytical study that was performed on 50 specimens of samples of triple-negative breast cancer. Data including age and sex, tumor grade, tumor size, types of invasion, GATA-3, and GCDFP-15 were assessed.Results:The mean age of the patients was 48.3±14.17 years. Of the total specimens, 46% were positive for GCDFP15 and 90% were positive for GATA-3. The intensity of GATA3 was evaluated and it was observed that 33(73.3%) of the cells were strongly stained and 12(26.7%) were weakly stained. There were no relationships between GATA-3 and GCDFP-15 with tumor characteristics.Conclusion:GATA-3 and GCDFP-15 may serve as diagnostic markers for triple-negative breast cancers and GATA-3 seems to be more reliable.