MicroRNAs (miRNA) are involved in the process of carcinogenesis, including the development of endometrial cancer (EC). This study aimed to investigate the association between the expression of three miRNAs (miR-21-5p, miR-205-5p, and miR-222-3p) in endometrial cancer tissues. In addition, the stability of expression of SNORD48 and U6, which were initially planned to be used as reference miRNAs for normalization, was investigated. Endometrial tissue was obtained from 111 patients with EC during hysterectomy and from 19 patients undergoing surgery for uterine fibroids or pelvic organ prolapse as a control group without neoplastic changes. Our study was based on calculations made with a digital PCR method (Qiagen, Hilden, Germany) to measure the absolute expression. In the endometrial cancer tissue, miR-205-5p was upregulated, while miR-222-3p and SNORD48 were downregulated compared to the control group. We detected statistically significant correlation of miR-205-5p, U6, and SNORD48 expression with different histological grades; the expression of miR-205-5p increases with the histopathological grade advancement (intraepithelial neoplasia- EIN = 1590, G1 = 3367.2, G2 = 8067 and G3 = 20,360), while U6 and SNORD expression decreases from EIN to G2 and increases again in the G3 grade (U6: EIN = 19,032, G1 = 16,482.4, G2 = 13,642.4, G3 = 133,008; SNORD48: EIN = 97,088, G1 = 59,520, G2 = 43,544, G3 = 227,200). Our study suggests that upregulation of miR-205-5p and downregulation of miR-222-3p and SNORD48 may influence development of endometrial cancer. Moreover, miR-205-5p, U6, and SNORD48 expression changes may be associated with progression of endometrial cancer. The results also indicate that SNORD48 and U6, commonly used as internal references, may influence endometrial cancer development and progression; therefore, they should not be used as references. However, it is important to note that further research is required to understand their role in endometrial cancer.
Keywords: SNORD48; U6; endometrial cancer; miR-205-5p; miR-21-5p; miR-222-3p; miRNA; reference gene.