Evaluation of Expression and Clinicopathological Relevance of Small Nucleolar RNAs (snoRNAs) in Invasive Breast Cancer

<b>Background/Objectives:</b> Breast cancer is a leading cause of cancer-related mortality among women worldwide. Small nucleolar RNAs (snoRNAs) represent a class of non-coding RNAs with potential as novel biomarkers applicable to improve diagnostic and prognostic applications. <b>Methods:</b> We performed a comprehensive evaluation of the snoRNA-related gene expression by qPCR using benign and tumor tissue samples associated with invasive breast carcinomas of no special type (NST). Selected candidate snoRNAs, i.e., SCARNA2, SCARNA3, SNORD15B, SNORD94, SNORA68, and SNHG1, along with RNU2-1 snRNA, were further validated and their associations with clinicopathological parameters were examined. External datasets and plasma samples were used for additional validation. <b>Results:</b> SCARNA2 was identified as the most promising snoRNA biomarker candidate, showing a positive association with better progression-free survival (PFS) in our data (13.3-month survival difference between low- and high-expression groups) and with both PFS and overall survival in external RNA-seq datasets. SNORD94, SNORD15B, SCARNA3, and RNU2-1 snRNA were also indicated as putative tumor suppressors. SNORD94 was associated with better progression-free survival (PFS) in our data as well (12.4-month survival difference between low- and high expression groups). Greater downregulation in the low-expression tumor subgroup compared to benign samples further supports the prognostic potential of SCARNA2 and SNORD94. Evidence for SNHG1 and SNORA68 as putative oncogenes was less conclusive. <b>Conclusions:</b> Several small nucleolar RNAs were found to be dysregulated in breast cancer specimens, supporting their further evaluation as potential biomarkers. In particular, SCARNA2, SNORD94, SNORD15B, SCARNA3, and RNU2-1 snRNA merit further investigation to determine their clinical relevance and biological roles in breast cancer.