en Cellular & Molecular Research Cellular & Molecular Research Original Research Original Research <strong>Background: </strong>GD2 synthase (GD2S) is the key enzyme required for ganglioside GD2 synthesis. It is commonly expressed in normal tissues and various cancers. Ganglioside GD2 is identified as a breast cancer stem cells (BCSCs) marker that promotes tumorigenesis. As GD2S has been found to be a useful molecular marker in neuroblastoma and retinoblastoma tumors, we suggest that it can be considered as a suitable candidate for the detection of CSCs in breast cancer tissues.<br> &nbsp;&nbsp;&nbsp; <strong>Methods:</strong> Expression of GD2S was examined in 65 breast tumors compared to adjacent normal tissues, applying quantitative real-time PCR (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA). The association between GD2S expression level and patients&rsquo; clinical characteristics was also assessed.<br> &nbsp;&nbsp; <strong>Results:</strong> Our findings showed that GD2S mRNA expression was significantly higher in breast cancer tissues in comparison to normal adjacent tissue samples (4.92-fold change, p<0.001) in advanced grades (p<0.001) and stages (p<0.001). It was also shown that GD2S protein expression was significantly higher in breast cancer tissues in comparison to normal adjacent tissues (4.86-fold change, p=0.010) in advanced grades (p=0.010), stages (p=0.005) and larger tumor size (p=0.002).<br> &nbsp;&nbsp; <strong>Conclusion:</strong> The current study showed that increased expression of GD2S in advanced breast cancer potentiates it as a promising tumor marker in these patients. Breast cancer, Cancer Stem Cells, ELISA, GD2 Synthase, qRT-PCR 1104 1112 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-648-3&slc_lang=en&sid=1 Maryam Mansoori maryammansoori1495@yahoo.com 200319475328460066108 200319475328460066108 No Department of Molecular Medicine, Faculty of Advanced Technologies in Medicine, & Oncopathology Research Center, Iran University of Medical Sciences (IUMS), Tehran, Iran Alireza Mirzaei mirzaeialireza26@gmail.com 200319475328460066109 200319475328460066109 No Bone and Joint Reconstruction Research Center, Shafa Orthopedic Hospital, Iran University of Medical Sciences, Tehran, Iran Isa Abdi Rad isaabdirad@yahoo.com 200319475328460066110 200319475328460066110 No Cellular and Molecular Research Center, Urmia University of Medical Sciences, Urmia, Iran Rahim Mahmodlou mahmodlou@gmail.com 200319475328460066111 200319475328460066111 No Department of Surgery, Imam Khomeini Hospital, Faculty of Medicine, Urmia University of Medical Sciences, Urmia, Iran Fatemeh Mansouri mansouri1600@hotmail.com 200319475328460066112 200319475328460066112 No Department of Genetics and Immunology, Faculty of Medicine, Urmia University of Medical Sciences, Urmia, Iran Leili Saeednejad Zanjani 200319475328460066113 200319475328460066113 No Oncopathology Research Center, Iran University of Medical Sciences (IUMS), Tehran, Iran Zeynab Asadi- Lari م zeynab.asadilari@yahoo.co.uk 200319475328460066114 200319475328460066114 No Department of Biology, Faculty of Science, University of Toronto, Toronto, Canada Zahra Madjd majdjabari.z@iums.ac.ir 200319475328460066115 200319475328460066115 No Department of Molecular Medicine, Faculty of Advanced Technologies in Medicine, & Oncopathology Research Center, Iran University of Medical Sciences (IUMS), Tehran, Iran