Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 58 9 2020 11 19 461 466 Ata Abbasi Department of Pathology, School of Medicine, Urmia University of Medical Sciences, Urmia, Iran Farahnaz Noroozinia Department of Pathology, School of Medicine, Urmia University of Medical Sciences, Urmia, Iran Sonia Hosseinzadeh Department of Pathology, School of Medicine, Urmia University of Medical Sciences, Urmia, Iran. Mohammad Amin Abbasi Firoozabadi Hospital Clinical Research Development Unit (FHCRDU), Iran University of Medical Sciences, Tehran, Iran Samira Anvar Department of Pathology, School of Medicine, Urmia University of Medical Sciences, Urmia, Iran Seyed Arman Seyed Mokhtari Student Research Committee, Urmia University of Medical Sciences, Urmia, Iran 2020 03 11 2020 05 05 We aimed to determine the frequency of Octamer binding transcription factor 4 (Oct4) expression in human invasive ductal carcinoma. 72 paraffin-embedded samples of breast cancer were enrolled. All blocks were stained for estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor 2(HER 2/neu), ki67, and Oct4 by immunohistochemistry (IHC) method. Of 72 enrolled cases, the mean age was 49.6±1.42 years. 18 (25%) of cases were luminal A, 14 (19.4%) were Her2 positive, 31 (43%) were luminal B, and 9 (12.5%) were triple-negative. IHC staining for Oct4 revealed no Oct4 expression in breast cancer samples. The staining was repeated twice, and seminoma was used as a positive control in each run. The results of both repeats were the same, and none of the examined samples showed Oct4 expression. We found no Oct4 expression in breast cancer samples examined in our study. We also did not find Oct4 expression in normal breast tissue. Our study is one of the few studies which has evaluated Oct4 expression in human breast cancer on tissue samples and is one of the least that has reported no expression of Oct4 in breast cancer. https://acta.tums.ac.ir/index.php/acta/article/view/8357