Abstract
Background/Objectives: The Notch signaling pathway regulates cell fate, proliferation, and differentiation, and its dysregulation has been implicated in various cancers, including breast cancer. MicroRNAs (miRNAs) are critical post-transcriptional regulators that can modulate Notch pathway components. The aim of this study was to identify miRNAs that may potentially regulate the expression of Notch pathway-related genes across five molecular subtypes of breast cancer in Polish women. Methods: Tumor and adjacent normal tissue samples were collected from 405 patients with five breast cancer subtypes: luminal A (n = 130), HER2-negative luminal B (n = 100), HER2-positive luminal B (n = 96), non-luminal HER2-positive (n = 36), and triple-negative breast cancer (n = 43). Gene expression was profiled using mRNA microarrays and validated with RT-qPCR and ELISA. Candidate regulatory miRNAs were identified by miRNA microarrays and confirmed using the miRDB database. Results: APH1A, CTBP1, DTX1, HEY1, HEY2, JAG2, NOTCH4, TLE2, and TLE4 were consistently dysregulated across all breast cancer subtypes. Overexpression of HEY1 and JAG2 may be driven by decreased levels of miR-145, miR-98, and miR-381. Conversely, downregulation of TLE4 may be associated with elevated expression of miR-196a and miR-155. No regulatory miRNAs meeting the selection criteria were identified for APH1A, CTBP1, DTX1, HEY2, NOTCH4, or TLE2. Conclusions: The consistent alterations suggest the presence of a shared Notch-driven oncogenic signature in breast cancer, potentially driving cell proliferation, stemness, and resistance to therapy. These findings enhance our understanding of Notch signaling in breast cancer and propose novel miRNA–Notch interactions as candidate targets for therapeutic intervention.