IntroductionColorectal cancer (CRC) is one of the most common types of cancer worldwide. The carcinogenesis of CRC is indeed complex, and there are many different mechanisms and pathways that contribute to the development of malignancy and the progression from primary to metastatic tumors. The OCT4A, encoded by thePOU5F1gene, is a transcription factor responsible for the phenotype of stem cells, maintaining pluripotency and regulation of differentiation. ThePOU5F1gene is made up of five exons that can create numerous isoforms through alternative promoter or alternative splicing. In addition toOCT4A, other isoforms calledOCT4Bare also translated into protein; however, their role in cells has been unclear. The aim of our work was to investigate the expression patterns ofOCT4isoforms in primary and metastatic CRC, providing us with useful information about their role in the development and progression of CRC.MethodsSurgical specimens from a total of 78 patients were collected and isolated from primary tumors (n= 47) and metastases (n= 31). The relative gene expression ofOCT4isoforms was investigated using the RT-qPCR method together with the TaqMan probes for particularOCT4isoforms.ResultsOur results suggest significantly downregulated expression of theOCT4AandOCT4Bsisoforms in both primary (p= 0.0002 andp< 0.0001, respectively) and metastatic tumors (p= 0.0006 andp= 0.00051, respectively) when compared with the control samples. We also observed a correlation between reduced expression of allOCT4isoforms and both primary and left-sided tumors (p= 0.001 andp= 0.030, respectively). On the other hand, the expression of allOCT4isoforms was significantly upregulated in metastases compared with primary tumors (p< 0.0001).DiscussionUnlike previous reports, we found out that the expression ofOCT4A,OCT4Bs, and allOCT4isoforms was significantly reduced in primary tumors and metastases compared with control samples. On the other hand, we supposed that the expression rate of allOCT4isoforms may be related to the cancer type and side, as well as to liver metastases. However, further studies are required to investigate the detailed expression patterns and significance of individualOCT4isoforms in carcinogenesis.